<?xml version="1.0" encoding="UTF-8"?>
<chapter xml:id="mvc"
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  <title>Web MVC framework</title>

  <section xml:id="mvc-introduction">
    <title>Introduction to Spring Web MVC framework</title>

    <para>The Spring Web model-view-controller (MVC) framework is designed
    around a <classname>DispatcherServlet</classname> that dispatches requests
    to handlers, with configurable handler mappings, view resolution, locale
    and theme resolution as well as support for uploading files. The default
    handler is based on the <interfacename>@Controller</interfacename> and
    <interfacename>@RequestMapping</interfacename> annotations, offering a
    wide range of flexible handling methods. With the introduction of Spring
    3.0, the <interfacename>@Controller</interfacename> mechanism also allows
    you to create RESTful Web sites and applications, through the
    <interfacename>@PathVariable</interfacename> annotation and other
    features.</para>

    <sidebar xml:id="mvc-open-for-extension">
      <title><quote>Open for extension...</quote></title>

      <para>A key design principle in Spring Web MVC and in Spring in general
      is the <quote><emphasis>Open for extension, closed for
      modification</emphasis></quote> principle.</para>

      <para>Some methods in the core classes of Spring Web MVC are marked
      <literal>final</literal>. As a developer you cannot override these
      methods to supply your own behavior. This has not been done arbitrarily,
      but specifically with this principle in mind.</para>

      <para>For an explanation of this principle, refer to <emphasis>Expert
      Spring Web MVC and Web Flow</emphasis> by Seth Ladd and others;
      specifically see the section "A Look At Design," on page 117 of the
      first edition. Alternatively, see</para>

      <orderedlist>
        <listitem>
          <para><link
          xl:href="http://www.objectmentor.com/resources/articles/ocp.pdf">Bob
          Martin, The Open-Closed Principle (PDF)</link></para>
        </listitem>
      </orderedlist>

      <para>You cannot add advice to final methods when you use Spring MVC.
      For example, you cannot add advice to the
      <literal>AbstractController.setSynchronizeOnSession()</literal> method.
      Refer to <xref linkend="aop-understanding-aop-proxies" /> for more
      information on AOP proxies and why you cannot add advice to final
      methods.</para>
    </sidebar>

    <para>In Spring Web MVC you can use any object as a command or
    form-backing object; you do not need to implement a framework-specific
    interface or base class. Spring's data binding is highly flexible: for
    example, it treats type mismatches as validation errors that can be
    evaluated by the application, not as system errors. Thus you need not
    duplicate your business objects' properties as simple, untyped strings in
    your form objects simply to handle invalid submissions, or to convert the
    Strings properly. Instead, it is often preferable to bind directly to your
    business objects.</para>

    <para>Spring's view resolution is extremely flexible. A
    <interfacename>Controller</interfacename> is typically responsible for
    preparing a model <classname>Map</classname> with data and selecting a
    view name but it can also write directly to the response stream and
    complete the request. View name resolution is highly configurable through
    file extension or Accept header content type negotiation, through bean
    names, a properties file, or even a custom
    <interfacename>ViewResolver</interfacename> implementation. The model (the
    M in MVC) is a <interfacename>Map</interfacename> interface, which allows
    for the complete abstraction of the view technology. You can integrate
    directly with template based rendering technologies such as JSP, Velocity
    and Freemarker, or directly generate XML, JSON, Atom, and many other types
    of content. The model <interfacename>Map</interfacename> is simply
    transformed into an appropriate format, such as JSP request attributes, a
    Velocity template model.</para>

    <section xml:id="mvc-features">
      <title>Features of Spring Web MVC<!--I moved Features of Spring Web MVC before Pluggability of other MVC implementations. You want to highlight your own imp. first.--></title>

      <!--Second line of sidebar refers to JSF; don't you mean JSP? Other refs in this context are to JSP. Also note, sidebar is read-only.-->

      <xi:include href="swf-sidebar.xml"
                  xmlns:xi="http://www.w3.org/2001/XInclude" />

      <para>Spring's web module includes many unique web support
      features:</para>

      <itemizedlist>
        <listitem>
          <para><emphasis>Clear separation of roles</emphasis>. Each role —
          controller, validator, command object, form object, model object,
          <classname>DispatcherServlet</classname>, handler mapping, view
          resolver, and so on — can be fulfilled by a specialized
          object.</para>
        </listitem>

        <listitem>
          <para><emphasis>Powerful and straightforward configuration of both
          framework and application classes as JavaBeans</emphasis>. This
          configuration capability includes easy referencing across contexts,
          such as from web controllers to business objects and
          validators.</para>
        </listitem>

        <listitem>
          <para><emphasis>Adaptability, non-intrusiveness, and
          flexibility.</emphasis> Define any controller method signature you
          need, possibly using one of the parameter annotations (such as
          @RequestParam, @RequestHeader, @PathVariable, and more) for a given
          scenario.</para>
        </listitem>

        <listitem>
          <para><emphasis>Reusable business code</emphasis>,<emphasis> no need
          for duplication</emphasis>. Use existing business objects as command
          or form objects instead of mirroring them to extend a particular
          framework base class.</para>
        </listitem>

        <listitem>
          <para><emphasis>Customizable binding and validation</emphasis>. Type
          mismatches as application-level validation errors that keep the
          offending value, localized date and number binding, and so on
          instead of String-only form objects with manual parsing and
          conversion to business objects.</para>
        </listitem>

        <listitem>
          <para><emphasis>Customizable handler mapping and view
          resolution</emphasis>. Handler mapping and view resolution
          strategies range from simple URL-based configuration, to
          sophisticated, purpose-built resolution strategies. Spring is more
          flexible than web MVC frameworks that mandate a particular
          technique.</para>
        </listitem>

        <listitem>
          <para><emphasis>Flexible model transfer</emphasis>. Model transfer
          with a name/value <interfacename>Map</interfacename> supports easy
          integration with any view technology.</para>
        </listitem>

        <listitem>
          <para><emphasis>Customizable locale and theme resolution, support
          for JSPs with or without Spring tag library, support for JSTL,
          support for Velocity without the need for extra bridges, and so
          on.</emphasis></para>
        </listitem>

        <listitem>
          <para><emphasis>A simple yet powerful JSP tag library known as the
          Spring tag library that provides support for features such as data
          binding and themes</emphasis>. The custom tags allow for maximum
          flexibility in terms of markup code. For information on the tag
          library descriptor, see the appendix entitled <xref
          linkend="spring.tld" /></para>
        </listitem>

        <listitem>
          <para><emphasis>A JSP form tag library, introduced in Spring 2.0,
          that makes writing forms in JSP pages much easier.</emphasis> For
          information on the tag library descriptor, see the appendix entitled
          <xref linkend="spring-form.tld" /></para>
        </listitem>

        <listitem>
          <para><emphasis>Beans whose lifecycle is scoped to the current HTTP
          request or HTTP <interfacename>Session</interfacename>.</emphasis>
          This is not a specific feature of Spring MVC itself, but rather of
          the <interfacename>WebApplicationContext</interfacename>
          container(s) that Spring MVC uses. These bean scopes are described
          in <xref linkend="beans-factory-scopes-other" /></para>
        </listitem>
      </itemizedlist>
    </section>

    <section xml:id="mvc-introduction-pluggability">
      <title>Pluggability of other MVC implementations</title>

      <para>Non-Spring MVC implementations are preferable for some projects.
      Many teams expect to leverage their existing investment in skills and
      tools. A large body of knowledge and experience exist for the Struts
      framework. If you can abide Struts' architectural flaws, it can be a
      viable choice for the web layer; the same applies to WebWork and other
      web MVC frameworks.</para>

      <para>If you do not want to use Spring's web MVC, but intend to leverage
      other solutions that Spring offers, you can integrate the web MVC
      framework of your choice with Spring easily. Simply start up a Spring
      root application context through its
      <classname>ContextLoaderListener</classname>, and access it through
      its<!--Identify *its*. do you mean root application context's?-->
      <interfacename>ServletContext</interfacename> attribute (or Spring's
      respective helper method) from within a Struts or WebWork action. No
      "plug-ins" are involved, so no dedicated integration is necessary. From
      the web layer's point of view, you simply use Spring as a library, with
      the root application context instance as the entry point.</para>

      <para>Your registered beans and Spring's services can be at your
      fingertips even without Spring's Web MVC. Spring does not compete with
      Struts or WebWork in this scenario. It simply addresses the many areas
      that the pure web MVC frameworks do not, from bean configuration to data
      access and transaction handling. So you can enrich your application with
      a Spring middle tier and/or data access tier, even if you just want to
      use, for example, the transaction abstraction with JDBC or
      Hibernate.</para>
    </section>
  </section>

  <section xml:id="mvc-servlet">
    <title>The <classname>DispatcherServlet</classname></title>

    <para>Spring's web MVC framework is, like many other web MVC frameworks,
    request-driven, designed around a central Servlet that dispatches requests
    to controllers and offers other functionality that facilitates the
    development of web applications. Spring's
    <classname>DispatcherServlet</classname> however, does more than just
    that. It is completely integrated with the Spring IoC container and as
    such allows you to use every other feature that Spring has.</para>

    <para>The request processing workflow of the Spring Web MVC
    <classname>DispatcherServlet</classname> is illustrated in the following
    diagram. The pattern-savvy reader will recognize that the
    <classname>DispatcherServlet</classname> is an expression of the
    <quote>Front Controller</quote> design pattern (this is a pattern that
    Spring Web MVC shares with many other leading web frameworks).</para>

    <para><mediaobject>
        <imageobject>
          <imagedata align="center" fileref="images/mvc.png" format="PNG" width="400"/>
        </imageobject>

        <caption><para>The request processing workflow in Spring Web MVC (high
        level)</para></caption>
      </mediaobject></para>

    <para>The <classname>DispatcherServlet</classname> is an actual
    <interfacename>Servlet</interfacename> (it inherits from the
    <classname>HttpServlet</classname> base class), and as such is declared in
    the <literal>web.xml</literal> of your web application. You need to map
    requests that you want the <classname>DispatcherServlet</classname> to
    handle, by using a URL mapping in the same <literal>web.xml</literal>
    file. This is standard Java EE Servlet configuration; the following example
    shows such a <classname>DispatcherServlet</classname> declaration and
    mapping:</para>

    <programlisting language="xml">&lt;web-app&gt;

    &lt;servlet&gt;
        &lt;servlet-name&gt;example&lt;/servlet-name&gt;
        &lt;servlet-class&gt;org.springframework.web.servlet.DispatcherServlet&lt;/servlet-class&gt;
        &lt;load-on-startup&gt;1&lt;/load-on-startup&gt;
    &lt;/servlet&gt;

    &lt;servlet-mapping&gt;
        &lt;servlet-name&gt;example&lt;/servlet-name&gt;
        &lt;url-pattern&gt;/example/*&lt;/url-pattern&gt;
    &lt;/servlet-mapping&gt;

&lt;/web-app&gt;</programlisting>

    <para>In the preceding example, all requests starting with
    <literal>/example</literal> will be handled by the
    <classname>DispatcherServlet</classname> instance named
    <literal>example</literal>.
    In a Servlet 3.0+ environment, you also have the
    option of configuring the Servlet container programmatically. Below is the code
    based equivalent of the above <filename>web.xml</filename> example:</para>

    <programlisting language="java">public class MyWebApplicationInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext container) {
        ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet());
        registration.setLoadOnStartup(1);
        registration.addMapping("/example/*");
    }

}</programlisting>

    <para><interfacename>WebApplicationInitializer</interfacename> is an interface
    provided by Spring MVC that ensures your code-based configuration is detected and
    automatically used to initialize any Servlet 3 container. An abstract base class
    implementation of this interace named
    <classname>AbstractDispatcherServletInitializer</classname> makes it even easier
    to register the <classname>DispatcherServlet</classname> by simply specifying
    its servlet mapping. See
    <link linkend="mvc-container-config">Code-based Servlet container initialization</link>
    for more details.</para>

    <para>The above is only the first step in setting up
    Spring Web MVC. <!--The discussion below is a little vague about what you're doing, when you do it, and what you're accomplishing. --><!-- Is the next step shown in the next example screen?-->You
    now need to configure the various beans used by the Spring Web MVC
    framework (over and above the <classname>DispatcherServlet</classname>
    itself).<!--See previous sentence. Add info to indicate where you find info that tells you how to configure beans for MVC framework. --><!--Next paragraph, so what are you telling them to *do* here? --></para>

    <para>As detailed in <xref linkend="context-introduction" />,
    <interfacename>ApplicationContext</interfacename> instances in Spring can
    be scoped. In the Web MVC framework, each
    <classname>DispatcherServlet</classname> has its own
    <interfacename>WebApplicationContext</interfacename>, which inherits all
    the beans already defined in the root
    <interfacename>WebApplicationContext</interfacename>. These inherited
    beans can be overridden in the servlet-specific scope, and you can define
    new scope-specific beans local to a given Servlet instance.</para>

    <para><mediaobject>
        <imageobject>
          <imagedata align="center" fileref="images/mvc-contexts.gif" format="GIF" width="400" />
        </imageobject>

        <caption>Context hierarchy in Spring Web MVC</caption>
      </mediaobject></para>

    <para>Upon initialization of a <classname>DispatcherServlet</classname>,
    Spring MVC looks for a file named <emphasis>
    <literal>[servlet-name]-servlet.xml</literal></emphasis> in the
    <literal>WEB-INF</literal> directory of your web application and creates
    the beans defined there, overriding the definitions of any beans defined
    with the same name in the global scope.</para>

    <para>Consider the following <classname>DispatcherServlet</classname>
    Servlet configuration (in the <literal>web.xml</literal> file):</para>

    <programlisting language="xml">&lt;web-app&gt;

    &lt;servlet&gt;
        &lt;servlet-name&gt;<emphasis role="bold">golfing</emphasis>&lt;/servlet-name&gt;
        &lt;servlet-class&gt;org.springframework.web.servlet.DispatcherServlet&lt;/servlet-class&gt;
        &lt;load-on-startup&gt;1&lt;/load-on-startup&gt;
    &lt;/servlet&gt;

    &lt;servlet-mapping&gt;
        &lt;servlet-name&gt;<emphasis role="bold">golfing</emphasis>&lt;/servlet-name&gt;
        &lt;url-pattern&gt;/golfing/*&lt;/url-pattern&gt;
    &lt;/servlet-mapping&gt;

&lt;/web-app&gt;</programlisting>

    <para>With the above Servlet configuration in place, <!--Is this something you need to do (in above example)? -->you
    will need to have a file called <literal>/WEB-INF/</literal><emphasis
    role="bold">golfing</emphasis><literal>-servlet.xml</literal> in your
    application; this file will contain all of your Spring Web MVC-specific
    components (beans). You can change the exact location of this
    configuration file through a Servlet initialization parameter (see below
    for details).</para>

    <!--See *where* for details? Give x-ref to section talks about how to change the location of the file through servlet init. param.-->

    <para>The <interfacename>WebApplicationContext</interfacename> is an
    extension of the plain <interfacename>ApplicationContext</interfacename>
    that has some extra features necessary for web applications. It differs
    from a normal <interfacename>ApplicationContext</interfacename> in that it
    is capable of resolving themes (see <xref linkend="mvc-themeresolver" />),
    and that it knows which Servlet it is associated with (by having a link to
    the <interfacename>ServletContext</interfacename>). The
    <interfacename>WebApplicationContext</interfacename> is bound in the
    <interfacename>ServletContext</interfacename>, and by using static methods
    on the <classname>RequestContextUtils</classname> class you can always
    look up the <interfacename>WebApplicationContext</interfacename> if you
    need access to it.</para>

    <section xml:id="mvc-servlet-special-bean-types">
        <title>Special Bean Types In the <interfacename>WebApplicationContext</interfacename></title>

        <para>The Spring <classname>DispatcherServlet</classname> uses special
        beans to process requests and render the appropriate views. These beans
        are part of Spring MVC. You can choose which special beans to use
        by simply configuring one or more of them in the
        <interfacename>WebApplicationContext</interfacename>.
        However, you don't need to do that initially since Spring MVC
        maintains a list of default beans to use if you don't configure any.
        More on that in the next section. First see the table below
        listing the special bean types the
        <classname>DispatcherServlet</classname> relies on.</para>

        <table xml:id="mvc-webappctx-special-beans-tbl">
          <title>Special bean types in the
          <interfacename>WebApplicationContext</interfacename></title>

          <tgroup cols="2">
            <colspec colname="c1" colwidth="1*" />

            <colspec colname="c2" colwidth="4*" />

            <thead>
              <row>
                <entry>Bean type</entry>

                <entry>Explanation</entry>
              </row>
            </thead>

            <tbody>
              <row>
                <entry><link linkend="mvc-handlermapping">HandlerMapping</link></entry>

                <entry>Maps incoming requests to handlers and a list of
                pre- and post-processors (handler interceptors) based on some
                criteria the details of which vary by <interfacename>HandlerMapping</interfacename>
                implementation. The most popular implementation supports
                annotated controllers but other implementations exists as well.</entry>
              </row>

              <row>
                <entry>HandlerAdapter</entry>

                <entry>Helps the <interfacename>DispatcherServlet</interfacename> to
                invoke a handler mapped to a request regardless of the handler
                is actually invoked. For example, invoking an annotated controller
                requires resolving various annotations. Thus the main purpose
                of a <interfacename>HandlerAdapter</interfacename> is to shield the
                <classname>DispatcherServlet</classname> from such details.</entry>
              </row>

              <row>
                <entry><link linkend="mvc-exceptionhandlers">HandlerExceptionResolver</link></entry>

                <entry>Maps exceptions to views also allowing for more
                complex exception handling code.</entry>
              </row>

              <row>
                <entry><link linkend="mvc-viewresolver">ViewResolver</link></entry>

                <entry>Resolves logical String-based view names to actual
                <interfacename>View</interfacename> types.</entry>
              </row>

              <row>
                <entry><link linkend="mvc-localeresolver">LocaleResolver</link></entry>

                <entry>Resolves the locale a client is using,
                in order to be able to offer internationalized views</entry>
              </row>

              <row>
                <entry><link linkend="mvc-themeresolver">ThemeResolver</link></entry>

                <entry>Resolves themes your web application can use, for
                example, to offer personalized layouts</entry>
              </row>

              <row>
                <entry><link linkend="mvc-multipart">MultipartResolver</link></entry>

                <entry>Parses multi-part requests for example to support processing
                file uploads from HTML forms.</entry>
              </row>

              <row>
                <entry><link linkend="mvc-flash-attributes">FlashMapManager</link></entry>

                <entry>Stores and retrieves the "input" and the "output"
                <classname>FlashMap</classname> that can be used to pass attributes
                from one request to another, usually across a redirect.</entry>
              </row>
            </tbody>
          </tgroup>
        </table>

    </section>

    <section xml:id="mvc-servlet-config">
        <title>Default DispatcherServlet Configuration</title>

        <para>As mentioned in the previous section for each special bean
        the <classname>DispatcherServlet</classname> maintains a list
        of implementations to use by default. This information is
        kept in the file <filename>DispatcherServlet.properties</filename>
        in the package <classname>org.springframework.web.servlet</classname>.
        </para>

        <para>All special beans have  some reasonable defaults of
        their own. Sooner or later though you'll need to customize
        one or more of the properties these beans provide.
        For example it's quite common to configure
        an <classname>InternalResourceViewResolver</classname>
        settings its <literal>prefix</literal> property to
        the parent location of view files.</para>

        <para>Regardless of the details, the important concept
        to understand here is that once
        you	configure a special bean such as an
        <classname>InternalResourceViewResolver</classname>
        in your <classname>WebApplicationContext</classname>, you
        effectively override the list of default implementations
        that would have been used otherwise for that special bean
        type. For example if you configure an
        <classname>InternalResourceViewResolver</classname>,
        the default list of <interfacename>ViewResolver</interfacename>
        implementations is ignored.
        </para>

        <para>In <xref linkend="mvc-config"/> you'll learn about
        other options for configuring Spring MVC including
        MVC Java config and the MVC XML namespace both of which provide
        a simple starting point and assume little knowledge of
        how Spring MVC works. Regardless of how you choose to
        configure your application, the concepts explained in this
        section are fundamental should be of help to you.
        </para>

    </section>

    <section xml:id="mvc-servlet-sequence">
        <title>DispatcherServlet Processing Sequence</title>

        <para>After you set up a <classname>DispatcherServlet</classname>, and a
        request comes in for that specific
        <classname>DispatcherServlet</classname>, the
        <classname>DispatcherServlet</classname> starts processing the request as
        follows:</para>

        <orderedlist>
          <listitem>
            <para>The <interfacename>WebApplicationContext</interfacename> is
            searched for and bound in the request as an attribute that the
            controller and other elements in the process can use. <!--Use to do *what*? Also revise to indicate *what* searches for the WebApplicationContext -->It
            is bound by default under the key
            <literal>DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE</literal>.</para>
          </listitem>

          <listitem>
            <para>The locale resolver is bound to the request to enable elements
            in the process to resolve the locale to use when processing the
            request (rendering the view, preparing data, and so on). If you do not
            need locale resolving, you do not need it.</para>

            <!--Reword 'if you don't need local resolving, you don't need to use it '. Are you saying locale resolving is optional? If you don't configure it, will this step occur?-->
          </listitem>

          <listitem>
            <para>The theme resolver is bound to the request to let elements such
            as views determine which theme to use. If you do not use themes, you
            can ignore it.</para>

            <!-- MLP perhaps say that there are not side effect to this binding, etc... Clarify *ignore it*. Does this step still occur if you don't use themes? -->

            <!--And what if you DO use themes, what do you do and when? Same question re locale resolving.-->
          </listitem>

          <listitem>
            <para>If you specify a multipart file resolver, the request is
            inspected for multiparts; if multiparts are found, the request is
            wrapped in a <classname>MultipartHttpServletRequest</classname> for
            further processing by other elements in the process. See <xref
            linkend="mvc-multipart" /> for further information about multipart
            handling.</para>
          </listitem>

          <listitem>
            <para>An appropriate handler is searched for. If a handler is found,
            the execution chain associated with the handler (preprocessors,
            postprocessors, and controllers) is executed in order to prepare a
            model or rendering.</para>
          </listitem>

          <listitem>
            <para>If a model is returned, the view is rendered. If no model is
            returned, (may be due to a preprocessor or postprocessor intercepting
            the request, perhaps for security reasons), no view is rendered,
            because the request could already have been fulfilled.</para>

            <!--fulfilled how and by what?-->
          </listitem>
        </orderedlist>

        <para>Handler exception resolvers that are declared in the
        <interfacename>WebApplicationContext</interfacename> pick up exceptions
        that are thrown during processing of the request. Using these exception
        resolvers allows you to define custom behaviors to address
        exceptions.</para>


        <para>The Spring <classname>DispatcherServlet</classname> also supports
        the return of the <emphasis>last-modification-date</emphasis>, as
        specified by the Servlet API. The process of determining the last
        modification date for a specific request is straightforward: the
        <classname>DispatcherServlet</classname> looks up an appropriate handler
        mapping and tests whether the handler that is found implements the
        <emphasis><interfacename>LastModified</interfacename></emphasis>
        interface. If so, the value of the <literal>long
        getLastModified(request)</literal> method of the
        <interfacename>LastModified</interfacename> interface is returned to the
        client.</para>

        <para>You can customize individual
        <classname>DispatcherServlet</classname> instances by adding Servlet
        initialization parameters (<literal>init-param</literal> elements) to the
        Servlet declaration in the <literal>web.xml</literal> file. See the
        following table for the list of supported parameters.</para>

        <!--Reword above sentence to specify whether configuring parameters in table configures last-modification-date, or are they further -->

        <!--customization for some other purpose? If so, need to explain how you config last-modification-date-->

        <table xml:id="mvc-disp-servlet-init-params-tbl">
          <title><classname>DispatcherServlet</classname> initialization
          parameters</title>

          <tgroup cols="2">
            <colspec colname="c1" colwidth="1*" />

            <colspec colname="c2" colwidth="4*" />

            <thead>
              <row>
                <entry>Parameter</entry>

                <entry>Explanation</entry>
              </row>
            </thead>

            <tbody>
              <row>
                <entry><literal>contextClass</literal></entry>

                <entry>Class that implements
                <interfacename>WebApplicationContext</interfacename>, which
                instantiates the context used by this Servlet. By default, the
                <classname>XmlWebApplicationContext</classname> is used.</entry>
              </row>

              <row>
                <entry><literal>contextConfigLocation</literal></entry>

                <entry>String that is passed to the context instance (specified by
                <literal>contextClass</literal>) to indicate where context(s) can
                be found. The string consists potentially of multiple strings
                (using a comma as a delimiter) to support multiple contexts. In
                case of multiple context locations with beans that are defined
                twice, the latest location takes precedence.</entry>

                <!-- MLP review -->
              </row>

              <row>
                <entry><literal>namespace</literal></entry>

                <entry>Namespace of the
                <interfacename>WebApplicationContext</interfacename>. Defaults to
                <literal>[servlet-name]-servlet</literal>.</entry>
              </row>
            </tbody>
          </tgroup>
        </table>
      </section>
  </section>

  <section xml:id="mvc-controller">
    <title>Implementing Controllers</title>

    <para>Controllers provide access to the application behavior that you
    typically define through a service interface. <!--I changed preceding to active voice because next sentence refers to user input. Thus *you* do some defining.-->Controllers
    interpret user input and transform it into a model that is represented to
    the user by the view. Spring implements a controller in a very abstract
    way, which enables you to create a wide variety of controllers.</para>

    <para>Spring 2.5 introduced an annotation-based programming model for MVC
    controllers that uses annotations such as
    <interfacename>@RequestMapping</interfacename>,
    <interfacename>@RequestParam</interfacename>,
    <interfacename>@ModelAttribute</interfacename>, and so on. This annotation
    support is available for both Servlet MVC and Portlet MVC. Controllers
    implemented in this style do not have to extend specific base classes or
    implement specific interfaces. Furthermore, they do not usually have
    direct dependencies on Servlet or Portlet APIs, although you can easily
    configure access to Servlet or Portlet facilities.</para>

    <tip>
      <para>Available in the <link linkend="new-in-3.0-samples">samples
      repository</link>, a number of web applications leverage the annotation
      support described in this section including
      <emphasis>MvcShowcase</emphasis>, <emphasis>MvcAjax</emphasis>,
      <emphasis>MvcBasic</emphasis>, <emphasis>PetClinic</emphasis>,
      <emphasis>PetCare</emphasis>, and others.</para>

      <!-- MLP Note removed reference to imagedb -->
    </tip>

    <!--You need an intro sentence here that indicates the *purpose* of the following code.  -->

    <programlisting language="java">@Controller
public class HelloWorldController {

    @RequestMapping("/helloWorld")
    public String helloWorld(Model model) {
        model.addAttribute("message", "Hello World!");
        return "helloWorld";
    }
}</programlisting>

    <para>As you can see, the <interfacename>@Controller</interfacename> and
    <interfacename>@RequestMapping</interfacename> annotations allow flexible
    method names and signatures. In this particular example the method accepts
    a <classname>Model</classname> and returns a view name as a
    <classname>String</classname>, but various other method parameters and
    return values can be used as explained later in this section.
    <interfacename>@Controller</interfacename> and
    <interfacename>@RequestMapping</interfacename> and a number of other
    annotations form the basis for the Spring MVC implementation. This section
    documents these annotations and how they are most commonly used in a
    Servlet environment.</para>

    <section xml:id="mvc-ann-controller">
      <title>Defining a controller with
      <interfacename>@Controller</interfacename></title>

      <para>The <interfacename>@Controller</interfacename> annotation
      indicates that a particular class serves the role of a
      <emphasis>controller</emphasis>. Spring does not require you to extend
      any controller base class or reference the Servlet API. However, you can
      still reference Servlet-specific features if you need to.</para>

      <para>The <interfacename>@Controller</interfacename> annotation acts as
      a stereotype for the annotated class, indicating its role. The
      dispatcher scans such annotated classes for mapped methods and detects
      <interfacename>@RequestMapping</interfacename> annotations (see the next
      section).</para>

      <para>You can define annotated controller beans explicitly, using a
      standard Spring bean definition in the dispatcher's context. However,
      the <interfacename>@Controller</interfacename> stereotype also allows
      for autodetection, aligned with Spring general support for detecting
      component classes in the classpath and auto-registering bean definitions
      for them.</para>

      <!-- MLP Bev.changed to 'also supports autodetection -->

      <para>To enable autodetection of such annotated controllers, you add
      component scanning to your configuration. Use the
      <emphasis>spring-context</emphasis> schema as shown in the following XML
      snippet:</para>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd"&gt;

    &lt;context:component-scan base-package="org.springframework.samples.petclinic.web"/&gt;

    <lineannotation>&lt;!-- ... --&gt;</lineannotation>

&lt;/beans&gt;</programlisting>
    </section>

    <section xml:id="mvc-ann-requestmapping">
      <title>Mapping Requests With
      <interfacename>@RequestMapping</interfacename></title>

      <para>You use the <interfacename>@RequestMapping</interfacename>
      annotation to map URLs such as <filename>/appointments</filename> onto
      an entire class or a particular handler method. Typically the
      class-level annotation maps a specific request path (or path pattern)
      onto a form controller, with additional method-level annotations
      narrowing the primary mapping for a specific HTTP method request method
      ("GET", "POST", etc.) or an HTTP request parameter condition.</para>

      <para>The following example from the <emphasis>Petcare</emphasis> sample
      shows a controller in a Spring MVC application that uses this
      annotation:</para>

      <programlisting language="java">@Controller
<emphasis role="bold">@RequestMapping("/appointments")</emphasis>
public class AppointmentsController {

    private final AppointmentBook appointmentBook;

    @Autowired
    public AppointmentsController(AppointmentBook appointmentBook) {
        this.appointmentBook = appointmentBook;
    }

    <emphasis role="bold">@RequestMapping(method = RequestMethod.GET)</emphasis>
    public Map&lt;String, Appointment&gt; get() {
        return appointmentBook.getAppointmentsForToday();
    }

    <emphasis role="bold">@RequestMapping(value="/{day}", method = RequestMethod.GET)</emphasis>
    public Map&lt;String, Appointment&gt; getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day, Model model) {
        return appointmentBook.getAppointmentsForDay(day);
    }

    <emphasis role="bold">@RequestMapping(value="/new", method = RequestMethod.GET)</emphasis>
    public AppointmentForm getNewForm() {
        return new AppointmentForm();
    }

    <emphasis role="bold">@RequestMapping(method = RequestMethod.POST)</emphasis>
    public String add(@Valid AppointmentForm appointment, BindingResult result) {
        if (result.hasErrors()) {
            return "appointments/new";
        }
        appointmentBook.addAppointment(appointment);
        return "redirect:/appointments";
    }
}</programlisting>

      <para>In the example, the <interfacename>@RequestMapping</interfacename>
      is used in a number of places. The first usage is on the type (class)
      level, which indicates that all handling methods on this controller are
      relative to the <filename>/appointments</filename> path. The
      <methodname>get()</methodname> method has a further
      <interfacename>@RequestMapping</interfacename> refinement: it only
      accepts GET requests, meaning that an HTTP GET for
      <filename>/appointments</filename> invokes this method. The
      <methodname>post()</methodname> has a similar refinement, and the
      <methodname>getNewForm()</methodname> combines the definition of HTTP
      method and path into one, so that GET requests for
      <filename>appointments/new</filename> are handled by that method.</para>

      <para>The <methodname>getForDay()</methodname> method shows another
      usage of <interfacename>@RequestMapping</interfacename>: URI templates.
      (See <link linkend="mvc-ann-requestmapping-uri-templates">the next
      section </link>).</para>

      <para>A <interfacename>@RequestMapping</interfacename> on the class
      level is not required. Without it, all paths are simply absolute, and
      not relative. The following example from the
      <emphasis>PetClinic</emphasis> sample application shows a multi-action
      controller using <classname>@RequestMapping</classname>:</para>

      <programlisting language="java">@Controller
public class ClinicController {

    private final Clinic clinic;

    @Autowired
    public ClinicController(Clinic clinic) {
        this.clinic = clinic;
    }

    <emphasis role="bold">@RequestMapping("/")</emphasis>
    public void welcomeHandler() {
    }

    <emphasis role="bold">@RequestMapping("/vets")</emphasis>
    public ModelMap vetsHandler() {
        return new ModelMap(this.clinic.getVets());
    }

}</programlisting>

      <tip>
        <title>Using <interfacename>@RequestMapping</interfacename> On
        Interface Methods</title>

        <para>A common pitfall when working with annotated controller classes
        happens when applying functionality that requires creating a proxy for
        the controller object (e.g.
        <interfacename>@Transactional</interfacename> methods). Usually you
        will introduce an interface for the controller in order to use JDK
        dynamic proxies. To make this work you must move the
        <interfacename>@RequestMapping</interfacename> annotations, as well as
        any other type and method-level annotations (e.g.
        <interfacename>@ModelAttribute</interfacename>,
        <interfacename>@InitBinder</interfacename>) to the
        interface as well as the mapping mechanism can only "see" the
        interface exposed by the proxy. Alternatively, you could activate
        <code>proxy-target-class="true"</code> in the configuration for the
        functionality applied to the controller (in our transaction scenario
        in <code>&lt;tx:annotation-driven /&gt;</code>). Doing so indicates
        that CGLIB-based subclass proxies should be used instead of
        interface-based JDK proxies. For more information on various proxying
        mechanisms see <xref linkend="aop-proxying" />.</para>

        <para>Note however that method argument annotations, e.g.
        <interfacename>@RequestParam</interfacename>, must be present in
        the method signatures of the controller class.</para>
      </tip>

      <section xml:id="mvc-ann-requestmapping-31-vs-30">
        <title>New Support Classes for <classname>@RequestMapping</classname> methods in Spring MVC 3.1</title>

        <para>Spring 3.1 introduced a new set of support classes for
        <classname>@RequestMapping</classname> methods called
        <classname>RequestMappingHandlerMapping</classname> and
        <classname>RequestMappingHandlerAdapter</classname> respectively.
        They are recommended for use and even required to take advantage of
        new features in Spring MVC 3.1 and going forward. The new support
        classes are enabled by default by the MVC namespace and the MVC Java
        config but must be configured explicitly if using neither.
        This section describes a few
        important differences between the old and the new support classes.
        </para>

        <para>Prior to Spring 3.1, type and method-level request mappings were
        examined in two separate stages -- a controller was selected first
        by the <classname>DefaultAnnotationHandlerMapping</classname> and the
        actual method to invoke was narrowed down second by
        the <classname>AnnotationMethodHandlerAdapter</classname>.</para>

        <para>With the new support classes in Spring 3.1, the
        <classname>RequestMappingHandlerMapping</classname> is the only place
        where a decision is made about which method should process the request.
        Think of controller methods as a collection of unique endpoints
        with mappings for each method derived from type and method-level
        <classname>@RequestMapping</classname> information.</para>

        <para>This enables some new possibilities. For once a
        <classname>HandlerInterceptor</classname> or a
        <classname>HandlerExceptionResolver</classname> can now expect the
        Object-based handler to be a <classname>HandlerMethod</classname>,
        which allows them to examine the exact method, its parameters and
        associated annotations. The processing for a URL no longer needs to
        be split across different controllers.
        </para>

        <para>There are also several things no longer possible:</para>
        <itemizedlist>
            <listitem><para>Select a controller first with a
            <classname>SimpleUrlHandlerMapping</classname> or
            <classname>BeanNameUrlHandlerMapping</classname> and then narrow
            the method based on <classname>@RequestMapping</classname>
            annotations.</para></listitem>
            <listitem><para>Rely on method names as a fall-back mechanism to
            disambiguate between two <classname>@RequestMapping</classname> methods
            that don't have an explicit path mapping URL path but otherwise
            match equally, e.g. by HTTP method. In the new support classes
            <classname>@RequestMapping</classname> methods have to be mapped
            uniquely.</para></listitem>
            <listitem><para>Have a single default method (without an explicit
            path mapping) with which requests are processed if no other
            controller method matches more concretely. In the new support
            classes if a matching method is not found a 404 error
            is raised.</para></listitem>
        </itemizedlist>

        <para>The above features are still supported with the existing support
        classes. However to take advantage of new Spring MVC 3.1 features
        you'll need to use the new support classes.</para>

      </section>

      <section xml:id="mvc-ann-requestmapping-uri-templates">
        <title>URI Template Patterns</title>

        <para><emphasis>URI templates</emphasis> can be used for convenient
        access to selected parts of a URL in a
        <interfacename>@RequestMapping</interfacename> method.</para>

        <para>A URI Template is a URI-like string, containing one or more
        variable names. When you substitute values for these variables, the
        template becomes a URI. The <link
        xl:href="http://bitworking.org/projects/URI-Templates/">proposed
        RFC</link> for URI Templates defines how a URI is parameterized. For
        example, the URI Template
        <code>http://www.example.com/users/{userId}</code> contains the
        variable <emphasis>userId</emphasis>. Assigning the value
        <emphasis>fred</emphasis> to the variable yields
        <code>http://www.example.com/users/fred</code>.</para>

        <para>In Spring MVC you can use the
        <interfacename>@PathVariable</interfacename> annotation on a method
        argument to bind it to the value of a URI template variable:</para>

        <programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(<emphasis role="bold">@PathVariable</emphasis> String ownerId, Model model) {
  Owner owner = ownerService.findOwner(ownerId);
  model.addAttribute("owner", owner);
  return "displayOwner";
}</programlisting>

        <para>The URI Template "<literal>/owners/{ownerId}</literal>"
        specifies the variable name <literal>ownerId</literal>. When the
        controller handles this request, the value of
        <literal>ownerId</literal> is set to the value found in the
        appropriate part of the URI. For example, when a request comes in for
        <code>/owners/fred</code>, the value of <literal>ownerId</literal> is
        <literal>fred</literal>.</para>

        <tip>
          <para>To process the @PathVariable annotation, Spring MVC needs to
          find the matching URI template variable by name. You can specify it
          in the annotation:</para>

          <programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(<emphasis role="bold">@PathVariable</emphasis>("ownerId") String theOwner, Model model) {
  // implementation omitted
}</programlisting>

          <para>Or if the URI template variable name matches the method
          argument name you can omit that detail. As long as your code is not
          compiled without debugging information, Spring MVC will match the
          method argument name to the URI template variable name:</para>

          <programlisting language="java">@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(<emphasis role="bold">@PathVariable</emphasis> String ownerId, Model model) {
  // implementation omitted
}</programlisting>
        </tip>

        <para>A method can have any number of
        <interfacename>@PathVariable</interfacename> annotations:</para>

        <programlisting language="java">@RequestMapping(value="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET)
public String findPet(<emphasis role="bold">@PathVariable</emphasis> String ownerId, <emphasis
            role="bold">@PathVariable</emphasis> String petId, Model model) {
  Owner owner = ownerService.findOwner(ownerId);
  Pet pet = owner.getPet(petId);
  model.addAttribute("pet", pet);
  return "displayPet";
}</programlisting>

        <para>When a <interfacename>@PathVariable</interfacename> annotation is
        used on a <classname>Map&lt;String, String&gt;</classname> argument, the
        map is populated with all URI template variables.
        </para>

        <para>A URI template can be assembled from type and path level
        <emphasis>@RequestMapping</emphasis> annotations. As a result the
        <methodname>findPet()</methodname> method can be invoked with a URL
        such as <filename>/owners/42/pets/21</filename>.</para>

        <programlisting language="java">@Controller
@RequestMapping(<emphasis role="bold">"/owners/{ownerId}"</emphasis>)
public class RelativePathUriTemplateController {

  @RequestMapping(<emphasis role="bold">"/pets/{petId}"</emphasis>)
  public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
    // implementation omitted
  }
}</programlisting>

        <para>A <interfacename>@PathVariable</interfacename> argument can be
        of <emphasis role="bold">any simple type</emphasis> such as int, long,
        Date, etc. Spring automatically converts to the appropriate type or
        throws a <classname>TypeMismatchException</classname> if it fails to
        do so. You can also register support for parsing additional data
        types. See <xref linkend="mvc-ann-typeconversion" /> and <xref
        linkend="mvc-ann-webdatabinder" />.</para>
      </section>

      <section xml:id="mvc-ann-requestmapping-uri-templates-regex">
        <title>URI Template Patterns with Regular Expressions</title>

        <para>Sometimes you need more precision in defining URI template
        variables. Consider the URL
        <code>"/spring-web/spring-web-3.0.5.jar"</code>. How do you break it
        down into multiple parts?</para>

        <para>The <interfacename>@RequestMapping</interfacename> annotation
        supports the use of regular expressions in URI template variables. The
        syntax is <code>{varName:regex}</code> where the first part defines
        the variable name and the second - the regular expression.For
        example:</para>

        <programlisting language="java">
@RequestMapping("/spring-web/{symbolicName:[a-z-]+}-{version:\\d\\.\\d\\.\\d}{extension:\\.[a-z]+}")
  public void handle(@PathVariable String version, @PathVariable String extension) {
    // ...
  }
}</programlisting>
      </section>

      <section xml:id="mvc-ann-requestmapping-patterns">
        <title>Path Patterns</title>

        <para>In addition to URI templates, the
        <interfacename>@RequestMapping</interfacename> annotation also
        supports Ant-style path patterns (for example,
        <filename>/myPath/*.do</filename>). A combination of URI templates and
        Ant-style globs is also supported (for example,
        <filename>/owners/*/pets/{petId}</filename>).</para>
      </section>

      <section xml:id="mvc-ann-requestmapping-placeholders">
        <title>Patterns with Placeholders</title>

        <para>Patterns in <interfacename>@RequestMapping</interfacename> annotations
        support ${...} placeholders against local properties and/or system properties
        and environment variables. This may be useful in cases where the path a
        controller is mapped to may need to be customized through configuration.
        For more information on placeholders see the Javadoc for
        <classname>PropertyPlaceholderConfigurer</classname>.</para>

      </section>

      <section xml:id="mvc-ann-matrix-variables">
        <title>Matrix Variables</title>

        <para>The URI specification
        <link xl:href="http://tools.ietf.org/html/rfc3986#section-3.3">RFC 3986</link>
        defines the possibility of including name-value pairs within path segments.
        There is no specific term used in the spec.
        The general "URI path parameters" could be applied although the more unique
        <link xl:href="http://www.w3.org/DesignIssues/MatrixURIs.html">"Matrix URIs"</link>,
        originating from an old post by Tim Berners-Lee, is also frequently used
        and fairly well known. Within Spring MVC these are referred to
        as matrix variables.</para>

        <para>Matrix variables can appear in any path segment, each matrix variable
        separated with a ";" (semicolon).
        For example: <code>"/cars;color=red;year=2012"</code>.
        Multiple values may be either "," (comma) separated
        <code>"color=red,green,blue"</code> or the variable name may be repeated
        <code>"color=red;color=green;color=blue"</code>.</para>

        <para>If a URL is expected to contain matrix variables, the request mapping
        pattern must represent them with a URI template.
        This ensures the request can be matched correctly regardless of whether
        matrix variables are present or not and in what order they are
        provided.</para>

        <para>Below is an example of extracting the matrix variable "q":</para>

        <programlisting language="java">// GET /pets/42;q=11;r=22

@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET)
public void findPet(@PathVariable String petId, @MatrixVariable int q) {

  // petId == 42
  // q == 11

}</programlisting>

       <para>Since all path segments may contain matrix variables, in some cases
       you need to be more specific to identify where the variable is expected to be:</para>

        <programlisting language="java">// GET /owners/42;q=11/pets/21;q=22

@RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET)
public void findPet(
    @MatrixVariable(value="q", pathVar="ownerId") int q1,
    @MatrixVariable(value="q", pathVar="petId") int q2) {

  // q1 == 11
  // q2 == 22

}</programlisting>

       <para>A matrix variable may be defined as optional and a default value specified:</para>

        <programlisting language="java">// GET /pets/42

@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET)
  public void findPet(@MatrixVariable(required=true, defaultValue="1") int q) {

    // q == 1

  }</programlisting>

        <para>All matrix variables may be obtained in a Map:</para>

        <programlisting language="java">// GET /owners/42;q=11;r=12/pets/21;q=22;s=23

@RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET)
  public void findPet(
        @MatrixVariable Map&lt;String, String&gt; matrixVars,
        @MatrixVariable(pathVar="petId"") Map&lt;String, String&gt; petMatrixVars) {

    // matrixVars: ["q" : [11,22], "r" : 12, "s" : 23]
    // petMatrixVars: ["q" : 11, "s" : 23]

  }</programlisting>

        <para>Note that to enable the use of matrix variables, you must set the
        <classname>removeSemicolonContent</classname> property of
        <classname>RequestMappingHandlerMapping</classname> to <code>false</code>.
        By default it is set to <code>true</code> with the exception of the
        MVC namespace and the MVC Java config both of which automatically enable
        the use of matrix variables.</para>

      </section>

      <section xml:id="mvc-ann-requestmapping-consumes">
        <title>Consumable Media Types</title>

        <para>You can narrow the primary mapping by specifying a list of
        consumable media types. The request will be matched only if the
        <emphasis>Content-Type</emphasis> request header matches the specified
        media type. For example:</para>

        <programlisting language="java">@Controller
@RequestMapping(value = "/pets", method = RequestMethod.POST, <emphasis
            role="bold">consumes="application/json"</emphasis>)
public void addPet(@RequestBody Pet pet, Model model) {
    // implementation omitted
}</programlisting>

        <para>Consumable media type expressions can also be negated as in
        <emphasis>!text/plain</emphasis> to match to all requests other than
        those with <emphasis>Content-Type</emphasis> of
        <emphasis>text/plain</emphasis>.</para>

        <tip>
          <para>The <emphasis>consumes</emphasis> condition is supported on
          the type and on the method level. Unlike most other conditions, when
          used at the type level, method-level consumable types override
          rather than extend type-level consumable types.</para>
        </tip>
      </section>

      <section xml:id="mvc-ann-requestmapping-produces">
        <title>Producible Media Types</title>

        <para>You can narrow the primary mapping by specifying a list of
        producible media types. The request will be matched only if the
        <emphasis>Accept</emphasis> request header matches one of these
        values. Furthermore, use of the <emphasis>produces</emphasis>
        condition ensures the actual content type used to generate the
        response respects the media types specified in the
        <emphasis>produces</emphasis> condition. For example:</para>

        <programlisting language="java">@Controller
@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, <emphasis
            role="bold">produces="application/json"</emphasis>)
@ResponseBody
public Pet getPet(@PathVariable String petId, Model model) {
    // implementation omitted
}</programlisting>

        <para>Just like with <emphasis>consumes</emphasis>, producible media
        type expressions can be negated as in <emphasis>!text/plain</emphasis>
        to match to all requests other than those with an
        <emphasis>Accept</emphasis> header value of
        <emphasis>text/plain</emphasis>.</para>

        <tip>
          <para>The <emphasis>produces</emphasis> condition is supported on
          the type and on the method level. Unlike most other conditions, when
          used at the type level, method-level producible types override
          rather than extend type-level producible types.</para>
        </tip>
      </section>

      <section xml:id="mvc-ann-requestmapping-params-and-headers">
        <title>Request Parameters and Header Values</title>

        <para>You can narrow request matching through request parameter
        conditions such as <code>"myParam"</code>, <code>"!myParam"</code>, or
        <code>"myParam=myValue"</code>. The first two test for request
        parameter presence/absence and the third for a specific parameter
        value. Here is an example with a request parameter value
        condition:</para>

        <programlisting language="java">@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {

  @RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, <emphasis
            role="bold">params="myParam=myValue"</emphasis>)
  public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
    // implementation omitted
  }
}</programlisting>

        <para>The same can be done to test for request header presence/absence
        or to match based on a specific request header value:</para>

        <programlisting language="java">@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {

@RequestMapping(value = "/pets", method = RequestMethod.GET, <emphasis
            role="bold">headers="myHeader=myValue"</emphasis>)
  public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
    // implementation omitted
  }
}</programlisting>

        <tip>
          <para>Although you can match to <emphasis>Content-Type</emphasis>
          and <emphasis>Accept</emphasis> header values using media type wild
          cards (for example <emphasis>"content-type=text/*"</emphasis> will
          match to <emphasis>"text/plain"</emphasis> and
          <emphasis>"text/html"</emphasis>), it is recommended to use the
          <emphasis>consumes</emphasis> and <emphasis>produces</emphasis>
          conditions respectively instead. They are intended specifically for
          that purpose.</para>
        </tip>
      </section>
    </section>

    <section xml:id="mvc-ann-methods">
      <title>Defining <interfacename>@RequestMapping</interfacename> handler
      methods</title>

      <para>An <classname>@RequestMapping</classname> handler method can have
      a very flexible signatures. The supported method arguments and return
      values are described in the following section. Most arguments can be
      used in arbitrary order with the only exception of
      <classname>BindingResult</classname> arguments. This is described in the
      next section.</para>

      <note><para>Spring 3.1 introduced a new set of support classes for
      <classname>@RequestMapping</classname> methods called
      <classname>RequestMappingHandlerMapping</classname> and
      <classname>RequestMappingHandlerAdapter</classname> respectively.
      They are recommended for use and even required to take advantage
      of new features in Spring MVC 3.1 and going forward.
      The new support classes are enabled by default from the MVC namespace and
      with use of the MVC Java config but must be
      configured explicitly if using neither.
      </para></note>

      <section xml:id="mvc-ann-arguments">
        <title>Supported method argument types</title>

        <para>The following are the supported method arguments: <itemizedlist>
            <listitem>
              <para>Request or response objects (Servlet API). Choose any
              specific request or response type, for example
              <interfacename>ServletRequest</interfacename> or
              <interfacename>HttpServletRequest</interfacename>.</para>
            </listitem>

            <listitem>
              <para>Session object (Servlet API): of type
              <interfacename>HttpSession</interfacename>. An argument of this
              type enforces the presence of a corresponding session. As a
              consequence, such an argument is never
              <literal>null</literal>.</para>

              <note>
                <para>Session access may not be thread-safe, in particular in
                a Servlet environment. Consider setting the
                <classname>RequestMappingHandlerAdapter</classname>'s
                "synchronizeOnSession" flag to "true" if multiple requests are
                allowed to access a session concurrently.</para>
              </note>
            </listitem>

            <listitem>
              <para><classname>org.springframework.web.context.request.WebRequest</classname>
              or
              <classname>org.springframework.web.context.request.NativeWebRequest</classname>.
              Allows for generic request parameter access as well as
              request/session attribute access, without ties to the native
              Servlet/Portlet API.</para>
            </listitem>

            <listitem>
              <para><classname>java.util.Locale</classname> for the current
              request locale, determined by the most specific locale resolver
              available, in effect, the configured
              <interfacename>LocaleResolver</interfacename> in a Servlet
              environment.</para>
            </listitem>

            <listitem>
              <para><classname>java.io.InputStream</classname> /
              <classname>java.io.Reader</classname> for access to the
              request's content. This value is the raw InputStream/Reader as
              exposed by the Servlet API.</para>
            </listitem>

            <listitem>
              <para><classname>java.io.OutputStream</classname> /
              <classname>java.io.Writer</classname> for generating the
              response's content. This value is the raw OutputStream/Writer as
              exposed by the Servlet API.</para>
            </listitem>

            <listitem>
              <para><interfacename>java.security.Principal</interfacename>
              containing the currently authenticated user.</para>
            </listitem>

            <listitem>
              <para><classname>@PathVariable</classname> annotated parameters
              for access to URI template variables. See <xref
              linkend="mvc-ann-requestmapping-uri-templates" />.</para>
            </listitem>

            <listitem>
              <para><classname>@MatrixVariable</classname> annotated parameters
              for access to name-value pairs located in URI path segments.
              See <xref linkend="mvc-ann-matrix-variables" />.</para>
            </listitem>

            <listitem>
              <para><classname>@RequestParam</classname> annotated parameters
              for access to specific Servlet request parameters. Parameter
              values are converted to the declared method argument type. See
              <xref linkend="mvc-ann-requestparam" />.</para>
            </listitem>

            <listitem>
              <para><interfacename>@RequestHeader</interfacename> annotated
              parameters for access to specific Servlet request HTTP headers.
              Parameter values are converted to the declared method argument
              type.</para>
            </listitem>

            <listitem>
              <para><interfacename>@RequestBody</interfacename> annotated
              parameters for access to the HTTP request body. Parameter values
              are converted to the declared method argument type using
              <interfacename>HttpMessageConverter</interfacename>s. See <xref
              linkend="mvc-ann-requestbody" />.</para>
            </listitem>

            <listitem>
              <para><interfacename>@RequestPart</interfacename> annotated
              parameters for access to the content of a "multipart/form-data"
              request part. See <xref
              linkend="mvc-multipart-forms-non-browsers" /> and <xref
              linkend="mvc-multipart" />.</para>
            </listitem>

            <listitem>
              <para><classname>HttpEntity&lt;?&gt;</classname> parameters for
              access to the Servlet request HTTP headers and contents. The
              request stream will be converted to the entity body using
              <interfacename>HttpMessageConverter</interfacename>s. See <xref
              linkend="mvc-ann-httpentity" />.</para>
            </listitem>

            <listitem>
              <para><interfacename>java.util.Map</interfacename> /
              <interfacename>org.springframework.ui.Model</interfacename> /
              <classname>org.springframework.ui.ModelMap</classname> for
              enriching the implicit model that is exposed to the web
              view.</para>
            </listitem>

            <listitem>
              <para><interfacename>org.springframework.web.servlet.mvc.support.RedirectAttributes</interfacename>
              to specify the exact set of attributes to use in case of a
              redirect and also to add flash attributes (attributes stored
              temporarily on the server-side to make them available to the
              request after the redirect).
              <literal>RedirectAttributes</literal> is used instead of the
              implicit model if the method returns a "redirect:" prefixed view
              name or <classname>RedirectView</classname>.</para>
            </listitem>

            <listitem>
              <para>Command or form objects to bind request parameters to bean
              properties (via setters) or directly to fields, with
              customizable type conversion, depending on
              <classname>@InitBinder</classname> methods and/or the
              HandlerAdapter configuration. See the
              <literal>webBindingInitializer</literal> property on
              <classname>RequestMappingHandlerAdapter</classname>. Such
              command objects along with their validation results will be
              exposed as model attributes by default, using the command class
              class name - e.g. model attribute "orderAddress" for a command
              object of type "some.package.OrderAddress". The
              <classname>ModelAttribute</classname> annotation can be used on
              a method argument to customize the model attribute name
              used.</para>
            </listitem>

            <listitem>
              <para><classname>org.springframework.validation.Errors</classname>
              /
              <classname>org.springframework.validation.BindingResult</classname>
              validation results for a preceding command or form object (the
              immediately preceding method argument).</para>
            </listitem>

            <listitem>
              <para><classname>org.springframework.web.bind.support.SessionStatus</classname>
              status handle for marking form processing as complete, which
              triggers the cleanup of session attributes that have been
              indicated by the <classname>@SessionAttributes</classname>
              annotation at the handler type level.</para>
            </listitem>

            <listitem>
              <para><classname>org.springframework.web.util.UriComponentsBuilder</classname>
              a builder for preparing a URL relative to the current request's
              host, port, scheme, context path, and the literal part of the
              servlet mapping.</para>
            </listitem>
          </itemizedlist></para>

        <para>The <interfacename>Errors</interfacename> or
        <interfacename>BindingResult</interfacename> parameters have to follow
        the model object that is being bound immediately as the method
        signature might have more that one model object and Spring will create
        a separate <interfacename>BindingResult</interfacename> instance for
        each of them so the following sample won't work:</para>

        <example>
          <title>Invalid ordering of BindingResult and @ModelAttribute</title>

          <programlisting language="java">@RequestMapping(method = RequestMethod.POST)
public String processSubmit(<emphasis role="bold">@ModelAttribute("pet") Pet pet</emphasis>,
    Model model, <emphasis role="bold">BindingResult result</emphasis>) { … }</programlisting>

          <para>Note, that there is a <interfacename>Model</interfacename>
          parameter in between <classname>Pet</classname> and
          <interfacename>BindingResult</interfacename>. To get this working
          you have to reorder the parameters as follows:</para>

          <programlisting language="java">@RequestMapping(method = RequestMethod.POST)
public String processSubmit(<emphasis role="bold">@ModelAttribute("pet") Pet pet</emphasis>,
    <emphasis role="bold">BindingResult result</emphasis>, Model model) { … }</programlisting>
        </example>
      </section>

      <section xml:id="mvc-ann-return-types">
        <title>Supported method return types</title>

        <para>The following are the supported return types: <itemizedlist>
            <listitem>
              <para>A <classname>ModelAndView</classname> object, with the
              model implicitly enriched with command objects and the results
              of <literal>@ModelAttribute</literal> annotated reference data
              accessor methods.</para>
            </listitem>

            <listitem>
              <para>A <interfacename>Model</interfacename> object, with the
              view name implicitly determined through a
              <interfacename>RequestToViewNameTranslator</interfacename> and
              the model implicitly enriched with command objects and the
              results of <literal>@ModelAttribute</literal> annotated
              reference data accessor methods.</para>
            </listitem>

            <listitem>
              <para>A <interfacename>Map</interfacename> object for exposing a
              model, with the view name implicitly determined through a
              <interfacename>RequestToViewNameTranslator</interfacename> and
              the model implicitly enriched with command objects and the
              results of <literal>@ModelAttribute</literal> annotated
              reference data accessor methods.</para>
            </listitem>

            <listitem>
              <para>A <interfacename>View</interfacename> object, with the
              model implicitly determined through command objects and
              <literal>@ModelAttribute</literal> annotated reference data
              accessor methods. The handler method may also programmatically
              enrich the model by declaring a
              <interfacename>Model</interfacename> argument (see above).<!--see above where? Need more explicit reference. same problem with next item.--></para>
            </listitem>

            <listitem>
              <para>A <classname>String</classname> value that is interpreted
              as the logical view name, with the model implicitly determined
              through command objects and <literal>@ModelAttribute</literal>
              annotated reference data accessor methods. The handler method
              may also programmatically enrich the model by declaring a
              <interfacename>Model</interfacename> argument (see
              above).</para>
            </listitem>

            <listitem>
              <para><literal>void</literal> if the method handles the response
              itself (by writing the response content directly, declaring an
              argument of type <interfacename>ServletResponse</interfacename>
              / <interfacename>HttpServletResponse</interfacename> for that
              purpose) or if the view name is supposed to be implicitly
              determined through a
              <interfacename>RequestToViewNameTranslator</interfacename> (not
              declaring a response argument in the handler method
              signature).</para>
            </listitem>

            <listitem>
              <para>If the method is annotated with
              <interfacename>@ResponseBody</interfacename>, the return type is
              written to the response HTTP body. The return value will be
              converted to the declared method argument type using
              <interfacename>HttpMessageConverter</interfacename>s. See <xref
              linkend="mvc-ann-responsebody" />.</para>
            </listitem>

            <listitem>
              <para>A <classname>HttpEntity&lt;?&gt;</classname> or
              <classname>ResponseEntity&lt;?&gt;</classname> object to provide
              access to the Servlet response HTTP headers and contents. The
              entity body will be converted to the response stream using
              <interfacename>HttpMessageConverter</interfacename>s. See <xref
              linkend="mvc-ann-httpentity" />.</para>
            </listitem>

            <listitem>
              <para>A <interfacename>Callable&lt;?&gt;</interfacename> can
              be returned when the application wants to produce the return
              value asynchronously in a thread managed by Spring MVC.</para>
            </listitem>

            <listitem>
              <para>A <classname>DeferredResult&lt;?&gt;</classname> can
              be returned when the application wants to produce the return
              value from a thread of its own choosing.</para>
            </listitem>

            <listitem>
              <para>Any other return type is considered to be a single model
              attribute to be exposed to the view, using the attribute name
              specified through <literal>@ModelAttribute</literal> at the
              method level (or the default attribute name based on the return
              type class name). The model is implicitly enriched with command
              objects and the results of <literal>@ModelAttribute</literal>
              annotated reference data accessor methods.</para>
            </listitem>

          </itemizedlist></para>
      </section>

      <section xml:id="mvc-ann-requestparam">
        <title>Binding request parameters to method parameters with
        <interfacename>@RequestParam</interfacename></title>

        <para>Use the <classname>@RequestParam</classname> annotation to bind
        request parameters to a method parameter in your controller.</para>

        <para>The following code snippet shows the usage:</para>

        <programlisting language="java">@Controller
@RequestMapping("/pets")
@SessionAttributes("pet")
public class EditPetForm {

    <lineannotation>// ...</lineannotation>

    @RequestMapping(method = RequestMethod.GET)
    public String setupForm(<emphasis role="bold">@RequestParam("petId") int petId</emphasis>, ModelMap model) {
        Pet pet = this.clinic.loadPet(petId);
        model.addAttribute("pet", pet);
        return "petForm";
    }

    <lineannotation>// ...</lineannotation></programlisting>

        <para>Parameters using this annotation are required by default, but
        you can specify that a parameter is optional by setting
        <interfacename>@RequestParam</interfacename>'s
        <literal>required</literal> attribute to <literal>false</literal>
        (e.g., <literal>@RequestParam(value="id",
        required=false)</literal>).</para>

        <para>Type conversion is applied automatically if the target method
        parameter type is not <classname>String</classname>. See <xref
        linkend="mvc-ann-typeconversion" />.</para>
      </section>

      <section xml:id="mvc-ann-requestbody">
        <title>Mapping the request body with the @RequestBody
        annotation</title>

        <para>The <classname>@RequestBody</classname> method parameter
        annotation indicates that a method parameter should be bound to the
        value of the HTTP request body. For example:</para>

        <programlisting language="java">@RequestMapping(value = "/something", method = RequestMethod.PUT)
public void handle(@RequestBody String body, Writer writer) throws IOException {
  writer.write(body);
}</programlisting>

        <para>You convert the request body to the method argument by using an
        <interfacename>HttpMessageConverter</interfacename>.
        <interfacename>HttpMessageConverter</interfacename> is responsible for
        converting from the HTTP request message to an object and converting
        from an object to the HTTP response body. The
        <classname>RequestMappingHandlerAdapter</classname> supports the
        <classname>@RequestBody</classname> annotation with the following
        default <interfacename>HttpMessageConverters</interfacename>:</para>

        <itemizedlist>
          <listitem>
            <para><classname>ByteArrayHttpMessageConverter</classname>
            converts byte arrays.</para>
          </listitem>

          <listitem>
            <para><classname>StringHttpMessageConverter</classname> converts
            strings.</para>
          </listitem>

          <listitem>
            <para><classname>FormHttpMessageConverter</classname> converts
            form data to/from a MultiValueMap&lt;String, String&gt;.</para>
          </listitem>

          <listitem>
            <para><classname>SourceHttpMessageConverter</classname> converts
            to/from a javax.xml.transform.Source.</para>
          </listitem>
        </itemizedlist>

        <para>For more information on these converters, see <link
        linkend="rest-message-conversion">Message Converters</link>. Also note
        that if using the MVC namespace or the MVC Java config, a wider
        range of message converters are registered by default.
        See <link linkend="mvc-config-enable">Enabling the MVC Java Config or
        the MVC XML Namespace</link> for more information.</para>

        <para>If you intend to read and write XML, you will need to configure
        the <classname>MarshallingHttpMessageConverter</classname> with a
        specific <interfacename>Marshaller</interfacename> and an
        <interfacename>Unmarshaller</interfacename> implementation from the
        <classname>org.springframework.oxm</classname> package. The example
        below shows how to do that directly in your configuration but if
        your application is configured through the MVC namespace or the
        MVC Java config see <link linkend="mvc-config-enable">Enabling
        the MVC Java Config or the MVC XML Namespace</link> instead.</para>

        <programlisting language="xml">&lt;bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"&gt;
    &lt;property name="messageConverters"&gt;
      &lt;util:list id="beanList"&gt;
        &lt;ref bean="stringHttpMessageConverter"/&gt;
        &lt;ref bean="marshallingHttpMessageConverter"/&gt;
      &lt;/util:list&gt;
    &lt;/property
&lt;/bean&gt;

&lt;bean id="stringHttpMessageConverter"
       class="org.springframework.http.converter.StringHttpMessageConverter"/&gt;

&lt;bean id="marshallingHttpMessageConverter"
      class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter"&gt;
  &lt;property name="marshaller" ref="castorMarshaller" /&gt;
  &lt;property name="unmarshaller" ref="castorMarshaller" /&gt;
&lt;/bean&gt;

&lt;bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/&gt;</programlisting>

        <para>An <classname>@RequestBody</classname> method parameter can be
        annotated with <classname>@Valid</classname>, in which case it will be
        validated using the configured <classname>Validator</classname>
        instance. When using the MVC namespace or the MVC Java config, a JSR-303 validator
        is configured automatically assuming a JSR-303 implementation is
        available on the classpath.</para>
        <para>Just like with <classname>@ModelAttribute</classname> parameters,
        an <classname>Errors</classname> argument can be used to examine the errors.
        If such an argument is not declared, a
        <classname>MethodArgumentNotValidException</classname> will be raised.
        The exception is handled in the
        <classname>DefaultHandlerExceptionResolver</classname>, which sends
        a <literal>400</literal> error back to the client.</para>

        <note>
          <para>Also see <link linkend="mvc-config-enable">Enabling the MVC
          Java Config or the MVC XML Namespace</link> for
          information on configuring message converters and a validator
          through the MVC namespace or the MVC Java config.</para>
        </note>
      </section>

      <section xml:id="mvc-ann-responsebody">
        <title>Mapping the response body with the
        <interfacename>@ResponseBody</interfacename> annotation</title>

        <para>The <interfacename>@ResponseBody</interfacename> annotation is
        similar to <interfacename>@RequestBody</interfacename>. This
        annotation can be put on a method and indicates that the return type
        should be written straight to the HTTP response body (and not placed
        in a Model, or interpreted as a view name). For example:</para>

        <programlisting language="java">@RequestMapping(value = "/something", method = RequestMethod.PUT)
@ResponseBody
public String helloWorld()  {
  return "Hello World";
}</programlisting>

        <para>The above example will result in the text <literal>Hello
        World</literal> being written to the HTTP response stream.</para>

        <para>As with <interfacename>@RequestBody</interfacename>, Spring
        converts the returned object to a response body by using an
        <interfacename>HttpMessageConverter</interfacename>. For more
        information on these converters, see the previous section and <link
        linkend="rest-message-conversion">Message Converters</link>.</para>
      </section>

      <section xml:id="mvc-ann-httpentity">
        <title>Using <classname>HttpEntity&lt;?&gt;</classname></title>

        <para>The <classname>HttpEntity</classname> is similar to
        <interfacename>@RequestBody</interfacename> and
        <interfacename>@ResponseBody</interfacename>. Besides getting access
        to the request and response body, <classname>HttpEntity</classname>
        (and the response-specific subclass
        <classname>ResponseEntity</classname>) also allows access to the
        request and response headers, like so:</para>

        <programlisting language="java">@RequestMapping("/something")
public ResponseEntity&lt;String&gt; handle(HttpEntity&lt;byte[]&gt; requestEntity) throws UnsupportedEncodingException {
  String requestHeader = requestEntity.getHeaders().getFirst("MyRequestHeader"));
  byte[] requestBody = requestEntity.getBody();
  // do something with request header and body

  HttpHeaders responseHeaders = new HttpHeaders();
  responseHeaders.set("MyResponseHeader", "MyValue");
  return new ResponseEntity&lt;String&gt;("Hello World", responseHeaders, HttpStatus.CREATED);
}</programlisting>

        <para>The above example gets the value of the
        <literal>MyRequestHeader</literal> request header, and reads the body
        as a byte array. It adds the <literal>MyResponseHeader</literal> to
        the response, writes <literal>Hello World</literal> to the response
        stream, and sets the response status code to 201 (Created).</para>

        <para>As with <interfacename>@RequestBody</interfacename> and
        <interfacename>@ResponseBody</interfacename>, Spring uses
        <interfacename>HttpMessageConverter</interfacename> to convert from
        and to the request and response streams. For more information on these
        converters, see the previous section and <link
        linkend="rest-message-conversion">Message Converters</link>.</para>
      </section>

      <section xml:id="mvc-ann-modelattrib-methods">
        <title>Using <interfacename>@ModelAttribute</interfacename> on a
        method</title>

        <para>The <interfacename>@ModelAttribute</interfacename> annotation
        can be used on methods or on method arguments. This section explains
        its usage on methods while the next section explains its usage on
        method arguments.</para>

        <para>An <interfacename>@ModelAttribute</interfacename> on a method
        indicates the purpose of that method is to add one or more model
        attributes. Such methods support the same argument types as
        <interfacename>@RequestMapping</interfacename> methods but cannot be
        mapped directly to requests. Instead
        <interfacename>@ModelAttribute</interfacename> methods in a controller
        are invoked before <interfacename>@RequestMapping</interfacename>
        methods, within the same controller. A couple of examples:</para>

        <programlisting language="java">
// Add one attribute
// The return value of the method is added to the model under the name "account"
// You can customize the name via @ModelAttribute("myAccount")

@ModelAttribute
public Account addAccount(@RequestParam String number) {
    return accountManager.findAccount(number);
}

// Add multiple attributes

@ModelAttribute
public void populateModel(@RequestParam String number, Model model) {
    model.addAttribute(accountManager.findAccount(number));
    // add more ...
}</programlisting>

        <para><interfacename>@ModelAttribute</interfacename> methods are used
        to populate the model with commonly needed attributes for example to
        fill a drop-down with states or with pet types, or to retrieve a
        command object like Account in order to use it to represent the data
        on an HTML form. The latter case is further discussed in the next
        section.</para>

        <para>Note the two styles of
        <interfacename>@ModelAttribute</interfacename> methods. In the first,
        the method adds an attribute implicitly by returning it. In the
        second, the method accepts a <classname>Model</classname> and adds any
        number of model attributes to it. You can choose between the two
        styles depending on your needs.</para>

        <para>A controller can have any number of
        <interfacename>@ModelAttribute</interfacename> methods. All such
        methods are invoked before
        <interfacename>@RequestMapping</interfacename> methods of the same
        controller.</para>

        <para><interfacename>@ModelAttribute</interfacename> methods can also
        be defined in an <interfacename>@ControllerAdvice</interfacename>-annotated
        class and such methods apply to all controllers.
        The <interfacename>@ControllerAdvice</interfacename> annotation is
        a component annotation allowing implementation classes to be autodetected
        through classpath scanning.</para>

        <tip>
          <para>What happens when a model attribute name is not explicitly
          specified? In such cases a default name is assigned to the model
          attribute based on its type. For example if the method returns an
          object of type <classname>Account</classname>, the default name used
          is "account". You can change that through the value of the
          <interfacename>@ModelAttribute</interfacename> annotation. If adding
          attributes directly to the <classname>Model</classname>, use the
          appropriate overloaded <literal>addAttribute(..)</literal> method -
          i.e., with or without an attribute name.</para>
        </tip>

        <para>The <interfacename>@ModelAttribute</interfacename> annotation
        can be used on <interfacename>@RequestMapping</interfacename> methods
        as well. In that case the return value of the
        <interfacename>@RequestMapping</interfacename> method is interpreted
        as a model attribute rather than as a view name. The view name is
        derived from view name conventions instead much like for methods
        returning void — see <xref linkend="mvc-coc-r2vnt" />.</para>
      </section>

      <section xml:id="mvc-ann-modelattrib-method-args">
        <title>Using <interfacename>@ModelAttribute</interfacename> on a
        method argument</title>

        <para>As explained in the previous section
        <interfacename>@ModelAttribute</interfacename> can be used on methods
        or on method arguments. This section explains its usage on method
        arguments.</para>

        <para>An <interfacename>@ModelAttribute</interfacename> on a method
        argument indicates the argument should be retrieved from the model. If
        not present in the model, the argument should be instantiated first
        and then added to the model. Once present in the model, the argument's
        fields should be populated from all request parameters that have
        matching names. This is known as data binding in Spring MVC, a very
        useful mechanism that saves you from having to parse each form field
        individually.</para>

        <programlisting language="java">
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(<emphasis role="bold">@ModelAttribute Pet pet</emphasis>) {

}</programlisting>

        <para>Given the above example where can the Pet instance come from?
        There are several options:</para>

        <itemizedlist>
          <listitem>
            <para>It may already be in the model due to use of
            <interfacename>@SessionAttributes</interfacename> — see <xref
            linkend="mvc-ann-sessionattrib" />.</para>
          </listitem>

          <listitem>
            <para>It may already be in the model due to an
            <interfacename>@ModelAttribute</interfacename> method in the same
            controller — as explained in the previous section.</para>
          </listitem>

          <listitem>
            <para>It may be retrieved based on a URI template variable and
            type converter (explained in more detail below).</para>
          </listitem>

          <listitem>
            <para>It may be instantiated using its default constructor.</para>
          </listitem>
        </itemizedlist>

        <para>An <interfacename>@ModelAttribute</interfacename> method is a
        common way to to retrieve an attribute from the database, which may
        optionally be stored between requests through the use of
        <interfacename>@SessionAttributes</interfacename>. In some cases it
        may be convenient to retrieve the attribute by using an URI template
        variable and a type converter. Here is an example:</para>

        <programlisting language="java">
@RequestMapping(value="/accounts/{account}", method = RequestMethod.PUT)
public String save(@ModelAttribute("account") Account account) {

}</programlisting>

        <para>In this example the name of the model attribute (i.e. "account")
        matches the name of a URI template variable. If you register
        <classname>Converter&lt;String, Account&gt;</classname> that can turn
        the <literal>String</literal> account value into an
        <classname>Account</classname> instance, then the above example will
        work without the need for an
        <interfacename>@ModelAttribute</interfacename> method.</para>

        <para>The next step is data binding. The
        <classname>WebDataBinder</classname> class matches request parameter
        names — including query string parameters and form fields — to model
        attribute fields by name. Matching fields are populated after type
        conversion (from String to the target field type) has been applied
        where necessary. Data binding and validation are covered in <xref
        linkend="validation" />. Customizing the data binding process for a
        controller level is covered in <xref
        linkend="mvc-ann-webdatabinder" />.</para>

        <para>As a result of data binding there may be errors such as missing
        required fields or type conversion errors. To check for such errors
        add a <classname>BindingResult</classname> argument immediately
        following the <interfacename>@ModelAttribute</interfacename>
        argument:</para>

        <programlisting language="java">
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(<emphasis role="bold">@ModelAttribute("pet") Pet pet</emphasis>, BindingResult result) {

    if (result.hasErrors()) {
        return "petForm";
    }

    // ...

}</programlisting>

        <para>With a <classname>BindingResult</classname> you can check if
        errors were found in which case it's common to render the same form
        where the errors can be shown with the help of Spring's
        <literal>&lt;errors&gt;</literal> form tag.</para>

        <para>In addition to data binding you can also invoke validation using
        your own custom validator passing the same
        <classname>BindingResult</classname> that was used to record data
        binding errors. That allows for data binding and validation errors to
        be accumulated in one place and subsequently reported back to the
        user:</para>

        <programlisting language="java">
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(<emphasis role="bold">@ModelAttribute("pet") Pet pet</emphasis>, BindingResult result) {

    new PetValidator().validate(pet, result);
    if (result.hasErrors()) {
        return "petForm";
    }

    // ...
}</programlisting>

        <para>Or you can have validation invoked automatically by adding the
        JSR-303 <interfacename>@Valid</interfacename> annotation:</para>

        <programlisting language="java">
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(<emphasis role="bold">@Valid @ModelAttribute("pet") Pet pet</emphasis>, BindingResult result) {

    if (result.hasErrors()) {
        return "petForm";
    }

    // ...
}</programlisting>

        <para>See <xref linkend="validation-beanvalidation" /> and <xref
        linkend="validation" /> for details on how to configure and use
        validation.</para>
      </section>

      <section xml:id="mvc-ann-sessionattrib">
        <title>Using <classname>@SessionAttributes</classname> to store model
        attributes in the HTTP session between requests</title>

        <para>The type-level <classname>@SessionAttributes</classname>
        annotation declares session attributes used by a specific handler.
        This will typically list the names of model attributes or types of
        model attributes which should be transparently stored in the session
        or some conversational storage, serving as form-backing beans between
        subsequent requests.</para>

        <para>The following code snippet shows the usage of this annotation,
        specifying the model attribute name:</para>

        <programlisting language="java">@Controller
@RequestMapping("/editPet.do")
<emphasis role="bold">@SessionAttributes("pet")</emphasis>
public class EditPetForm {
    <lineannotation>// ...</lineannotation>
}</programlisting>

        <note>
          <para>When using controller interfaces (e.g., for AOP proxying),
          make sure to consistently put <emphasis>all</emphasis> your mapping
          annotations - such as <interfacename>@RequestMapping</interfacename>
          and <interfacename>@SessionAttributes</interfacename> - on the
          controller <emphasis>interface</emphasis> rather than on the
          implementation class.</para>
        </note>
      </section>

      <section xml:id="mvc-ann-redirect-attributes">
        <title>Specifying redirect and flash attributes</title>

        <para>By default all model attributes are considered to be exposed as
        URI template variables in the redirect URL. Of the remaining
        attributes those that are primitive types or collections/arrays of
        primitive types are automatically appended as query parameters.</para>

        <para>In annotated controllers however the model may contain
        additional attributes originally added for rendering purposes (e.g.
        drop-down field values). To gain precise control over the attributes
        used in a redirect scenario, an
        <interfacename>@RequestMapping</interfacename> method can declare an
        argument of type <interfacename>RedirectAttributes</interfacename> and
        use it to add attributes for use in
        <classname>RedirectView</classname>. If the controller method does
        redirect, the content of
        <interfacename>RedirectAttributes</interfacename> is used. Otherwise
        the content of the default <interfacename>Model</interfacename> is
        used.</para>

        <para>The <classname>RequestMappingHandlerAdapter</classname> provides
        a flag called <literal>"ignoreDefaultModelOnRedirect"</literal> that
        can be used to indicate the content of the default
        <interfacename>Model</interfacename> should never be used if a
        controller method redirects. Instead the controller method should
        declare an attribute of type
        <interfacename>RedirectAttributes</interfacename> or if it doesn't do
        so no attributes should be passed on to
        <classname>RedirectView</classname>. Both the MVC namespace and the
        MVC Java config keep this flag set to <literal>false</literal> in order to maintain
        backwards compatibility. However, for new applications we recommend
        setting it to <literal>true</literal></para>

        <para>The <interfacename>RedirectAttributes</interfacename> interface
        can also be used to add flash attributes. Unlike other redirect
        attributes, which end up in the target redirect URL, flash attributes
        are saved in the HTTP session (and hence do not appear in the URL).
        The model of the controller serving the target redirect URL
        automatically receives these flash attributes after which they are
        removed from the session. See <xref linkend="mvc-flash-attributes" />
        for an overview of the general support for flash attributes in Spring
        MVC.</para>
      </section>

      <section xml:id="mvc-ann-form-urlencoded-data">
        <title>Working with
        <literal>"application/x-www-form-urlencoded"</literal> data</title>

        <para>The previous sections covered use of
        <interfacename>@ModelAttribute</interfacename> to support form
        submission requests from browser clients. The same annotation is
        recommended for use with requests from non-browser clients as well.
        However there is one notable difference when it comes to working with
        HTTP PUT requests. Browsers can submit form data via HTTP GET or HTTP
        POST. Non-browser clients can also submit forms via HTTP PUT. This
        presents a challenge because the Servlet specification requires the
        <literal>ServletRequest.getParameter*()</literal> family of methods to
        support form field access only for HTTP POST, not for HTTP PUT.</para>

        <para>To support HTTP PUT and PATCH requests, the <literal>spring-web</literal>
        module provides the filter
        <classname>HttpPutFormContentFilter</classname>, which can be
        configured in <filename>web.xml</filename>:</para>

        <programlisting language="xml">&lt;filter&gt;
  &lt;filter-name&gt;httpPutFormFilter&lt;/filter-name&gt;
  &lt;filter-class&gt;org.springframework.web.filter.HttpPutFormContentFilter&lt;/filter-class&gt;
&lt;/filter&gt;

&lt;filter-mapping&gt;
  &lt;filter-name&gt;httpPutFormFilter&lt;/filter-name&gt;
  &lt;servlet-name&gt;dispatcherServlet&lt;/servlet-name&gt;
&lt;/filter-mapping&gt;

&lt;servlet&gt;
  &lt;servlet-name&gt;dispatcherServlet&lt;/servlet-name&gt;
  &lt;servlet-class&gt;org.springframework.web.servlet.DispatcherServlet&lt;/servlet-class&gt;
&lt;/servlet&gt;</programlisting>

        <para>The above filter intercepts HTTP PUT and PATCH requests with content type
        <literal>application/x-www-form-urlencoded</literal>, reads the form
        data from the body of the request, and wraps the
        <classname>ServletRequest</classname> in order to make the form data
        available through the
        <literal>ServletRequest.getParameter*()</literal> family of
        methods.</para>

        <note>
          <para>As <classname>HttpPutFormContentFilter</classname> consumes the body of the
          request, it should not be configured for PUT or PATCH URLs that rely on other
          converters for <literal>application/x-www-form-urlencoded</literal>. This includes
          <literal>@RequestBody MultiValueMap&lt;String, String&gt;</literal> and
          <literal>HttpEntity&lt;MultiValueMap&lt;String, String&gt;&gt;</literal>.</para>
        </note>
      </section>

      <section xml:id="mvc-ann-cookievalue">
        <title>Mapping cookie values with the @CookieValue annotation</title>

        <para>The <interfacename>@CookieValue</interfacename> annotation
        allows a method parameter to be bound to the value of an HTTP
        cookie.</para>

        <para>Let us consider that the following cookie has been received with
        an http request:</para>

        <programlisting>JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84</programlisting>

        <para>The following code sample demonstrates how to get the value of
        the <literal>JSESSIONID</literal> cookie:</para>

        <programlisting language="java">@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(<emphasis role="bold">@CookieValue("JSESSIONID")</emphasis> String cookie)  {

  //...

}</programlisting>

        <para>Type conversion is applied automatically if the target method
        parameter type is not <classname>String</classname>. See <xref
        linkend="mvc-ann-typeconversion" />.</para>

        <para>This annotation is supported for annotated handler methods in
        Servlet and Portlet environments.</para>
      </section>

      <section xml:id="mvc-ann-requestheader">
        <title>Mapping request header attributes with the @RequestHeader
        annotation</title>

        <para>The <interfacename>@RequestHeader</interfacename> annotation
        allows a method parameter to be bound to a request header.</para>

        <para>Here is a sample request header:</para>

        <programlisting>
Host                    localhost:8080
Accept                  text/html,application/xhtml+xml,application/xml;q=0.9
Accept-Language         fr,en-gb;q=0.7,en;q=0.3
Accept-Encoding         gzip,deflate
Accept-Charset          ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive              300</programlisting>

        <para>The following code sample demonstrates how to get the value of
        the <literal>Accept-Encoding</literal> and
        <literal>Keep-Alive</literal> headers:</para>

        <programlisting language="java">@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(<emphasis role="bold">@RequestHeader("Accept-Encoding")</emphasis> String encoding,
                              <emphasis role="bold">@RequestHeader("Keep-Alive")</emphasis> long keepAlive)  {

  //...

}</programlisting>

        <para>Type conversion is applied automatically if the method parameter
        is not <classname>String</classname>. See <xref
        linkend="mvc-ann-typeconversion" />.</para>

        <tip>
          <para>Built-in support is available for converting a comma-separated
          string into an array/collection of strings or other types known to
          the type conversion system. For example a method parameter annotated
          with <literal>@RequestHeader("Accept")</literal> may be of type
          <classname>String</classname> but also
          <classname>String[]</classname> or
          <classname>List&lt;String&gt;</classname>.</para>
        </tip>

        <para>This annotation is supported for annotated handler methods in
        Servlet and Portlet environments.</para>
      </section>

      <section xml:id="mvc-ann-typeconversion">
        <title>Method Parameters And Type Conversion</title>

        <para>String-based values extracted from the request including request
        parameters, path variables, request headers, and cookie values may
        need to be converted to the target type of the method parameter or
        field (e.g., binding a request parameter to a field in an
        <interfacename>@ModelAttribute</interfacename> parameter) they're
        bound to. If the target type is not <classname>String</classname>,
        Spring automatically converts to the appropriate type. All simple
        types such as int, long, Date, etc. are supported. You can further
        customize the conversion process through a
        <classname>WebDataBinder</classname> (see <xref
        linkend="mvc-ann-webdatabinder" />) or by registering
        <classname>Formatters</classname> with the
        <classname>FormattingConversionService</classname> (see <xref
        linkend="format" />).</para>
      </section>

      <section xml:id="mvc-ann-webdatabinder">
        <title>Customizing <classname>WebDataBinder</classname>
        initialization</title>

        <para>To customize request parameter binding with PropertyEditors
        through Spring's <classname>WebDataBinder</classname>, you can use
        <interfacename>@InitBinder</interfacename>-annotated methods within
        your controller, <interfacename>@InitBinder</interfacename> methods
        within an <interfacename>@ControllerAdvice</interfacename> class,
        or provide a custom
        <interfacename>WebBindingInitializer</interfacename>.</para>

        <section xml:id="mvc-ann-initbinder">
          <title>Customizing data binding with
          <interfacename>@InitBinder</interfacename></title>

          <para>Annotating controller methods with
          <interfacename>@InitBinder</interfacename> allows you to configure
          web data binding directly within your controller class.
          <interfacename>@InitBinder</interfacename> identifies methods that
          initialize the <classname>WebDataBinder</classname> that will be
          used to populate command and form object arguments of annotated
          handler methods.</para>

          <para>Such init-binder methods support all arguments that
          <interfacename>@RequestMapping</interfacename> supports, except for
          command/form objects and corresponding validation result objects.
          Init-binder methods must not have a return value. Thus, they are
          usually declared as <literal>void</literal>. Typical arguments
          include <classname>WebDataBinder</classname> in combination with
          <interfacename>WebRequest</interfacename> or
          <classname>java.util.Locale</classname>, allowing code to register
          context-specific editors.</para>

          <para>The following example demonstrates the use of
          <interfacename>@InitBinder</interfacename> to configure a
          <classname>CustomDateEditor</classname> for all
          <classname>java.util.Date</classname> form properties.</para>

          <programlisting language="java">@Controller
public class MyFormController {

    <emphasis role="bold">@InitBinder</emphasis>
    public void initBinder(WebDataBinder binder) {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
        dateFormat.setLenient(false);
        binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
    }

    <lineannotation>// ...</lineannotation>
}</programlisting>
        </section>

        <section xml:id="mvc-ann-webbindinginitializer">
          <title>Configuring a custom
          <interfacename>WebBindingInitializer</interfacename></title>

          <para>To externalize data binding initialization, you can provide a
          custom implementation of the
          <interfacename>WebBindingInitializer</interfacename> interface,
          which you then enable by supplying a custom bean configuration for
          an <classname>AnnotationMethodHandlerAdapter</classname>, thus
          overriding the default configuration.</para>

          <para>The following example from the PetClinic application shows a
          configuration using a custom implementation of the
          <interfacename>WebBindingInitializer</interfacename> interface,
          <classname>org.springframework.samples.petclinic.web.ClinicBindingInitializer</classname>,
          which configures PropertyEditors required by several of the
          PetClinic controllers.</para>

          <programlisting language="xml">&lt;bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"&gt;
    &lt;property name="cacheSeconds" value="0" /&gt;
    &lt;property name="webBindingInitializer"&gt;
        &lt;bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" /&gt;
    &lt;/property&gt;
&lt;/bean&gt;</programlisting>
        </section>

        <section xml:id="mvc-ann-initbinder-advice">
          <title>Customizing data binding with externalized
          <interfacename>@InitBinder</interfacename> methods</title>

          <para><interfacename>@InitBinder</interfacename> methods can also
          be defined in an <interfacename>@ControllerAdvice</interfacename>-annotated
          class in which case they apply to all controllers. This provides an
          alternative to using a <interfacename>WebBindingInitializer</interfacename>.
          </para>

          <para>The <interfacename>@ControllerAdvice</interfacename> annotation is
          a component annotation allowing implementation classes to be autodetected
          through classpath scanning.</para>
        </section>

      </section>

      <section xml:id="mvc-ann-lastmodified">
        <title>Support for the 'Last-Modified' Response Header To Facilitate
        Content Caching</title>

        <para>An <interfacename>@RequestMapping</interfacename> method may
        wish to support <literal>'Last-Modified'</literal> HTTP requests, as
        defined in the contract for the Servlet API's
        <literal>getLastModified</literal> method, to facilitate content
        caching. This involves calculating a lastModified
        <literal>long</literal> value for a given request, comparing it
        against the <literal>'If-Modified-Since'</literal> request header
        value, and potentially returning a response with status code 304 (Not
        Modified). An annotated controller method can achieve that as
        follows:</para>

        <programlisting language="java">
@RequestMapping
public String myHandleMethod(WebRequest webRequest, Model model) {

    long lastModified = // 1. application-specific calculation

    if (request.checkNotModified(lastModified)) {
        // 2. shortcut exit - no further processing necessary
        return null;
     }

    // 3. or otherwise further request processing, actually preparing content
    model.addAttribute(...);
    return "myViewName";
}</programlisting>

        <para>There are two key elements to note: calling
        <code>request.checkNotModified(lastModified)</code> and returning
        <literal>null</literal>. The former sets the response status to 304
        before it returns <literal>true</literal>. The latter, in combination
        with the former, causes Spring MVC to do no further processing of the
        request.</para>
      </section>
    </section>

    <section xml:id="mvc-ann-async">
      <title>Asynchronous Request Processing</title>

      <para>Spring MVC 3.2 introduced Servlet 3 based asynchronous request
      processing. Instead of returning a value, as usual, a controller method
      can now return a <interfacename>java.util.concurrent.Callable</interfacename>
      and produce the return value from a separate thread. Meanwhile the main Servlet
      container thread is released and allowed to process other requests.
      Spring MVC invokes the <interfacename>Callable</interfacename> in a
      separate thread with the help of a <interfacename>TaskExecutor</interfacename>
      and when the <interfacename>Callable</interfacename> returns, the
      request is dispatched back to the Servlet container to resume
      processing with the value returned by the
      <interfacename>Callable</interfacename>.
      Here is an example controller method:</para>

      <programlisting language="java">
@RequestMapping(method=RequestMethod.POST)
public Callable&lt;String&gt; processUpload(final MultipartFile file) {

  return new Callable&lt;String&gt;() {
    public Object call() throws Exception {
      // ...
      return "someView";
    }
  };
}</programlisting>

      <para>A second option is for the controller to return an instance of
      <classname>DeferredResult</classname>. In this case the return value
      will also be produced from a separate thread. However, that thread is not
      known to Spring MVC. For example the result may be produced in response
      to some external event such as a JMS message, a scheduled task, etc.
      Here is an example controller method:</para>

      <programlisting language="java">
@RequestMapping("/quotes")
@ResponseBody
public DeferredResult&lt;String&gt; quotes() {
  DeferredResult&lt;String&gt; deferredResult = new DeferredResult&lt;String&gt;();
  // Save the deferredResult in in-memory queue ...
  return deferredResult;
}

// In some other thread...
deferredResult.setResult(data);
</programlisting>

      <para>This may be difficult to understand without any knowledge of the
      Servlet 3 async processing feature. It would certainly help to read up on it.
      At a very minimum consider the following basic facts:</para>

      <itemizedlist>
        <listitem>
          <para>A <interfacename>ServletRequest</interfacename>
          can be put in asynchronous mode by calling
          <code>request.startAsync()</code>. The main effect of doing so is
          that the Servlet, as well as any Filters, can exit but the response
          will remain open allowing some other thread to complete processing.
          </para>
        </listitem>
        <listitem>
          <para>The call to <code>request.startAsync()</code> returns an
          <interfacename>AsyncContext</interfacename>, which can be used for
          further control over async processing. For example it provides
          the method <code>dispatch</code>, which can be called from an
          application thread in order to "dispatch" the request back to
          the Servlet container. An async dispatch is similar to a forward
          except it is made from one (application) thread to another
          (Servlet container) thread whereas a forward occurs synchronously
          in the same (Servlet container) thread.</para>
        </listitem>
        <listitem>
          <para><interfacename>ServletRequest</interfacename> provides access
          to the current <interfacename>DispatcherType</interfacename>, which
          can be used to distinguish if a <interfacename>Servlet</interfacename> or
          a <interfacename>Filter</interfacename> is processing on
          the initial request processing thread and when it is processing in
          an async dispatch.</para>
        </listitem>
      </itemizedlist>

      <para>With the above in mind, the following is the sequence
      of events for async request processing with a <interfacename>Callable</interfacename>:
      (1) Controller returns a
      <interfacename>Callable</interfacename>, (2) Spring MVC starts async processing
      and submits the <interfacename>Callable</interfacename>
      to a <interfacename>TaskExecutor</interfacename>
      for processing in a separate thread, (3) the <classname>DispatcherServlet</classname>
      and all Filter's exit the request processing thread but the response
      remains open, (4) the <interfacename>Callable</interfacename> produces a result
      and Spring MVC dispatches the request back to the Servlet container,
      (5) the <classname>DispatcherServlet</classname> is invoked again and processing
      resumes with the asynchronously produced result from the
      <interfacename>Callable</interfacename>. The exact sequencing of (2),
      (3), and (4) may vary depending on the speed of execution of the
      concurrent threads.
      </para>

      <para>The sequence of events for async request processing with a
      <classname>DeferredResult</classname> is the same in principal except
      it's up to the application to produce the asynchronous result from some thread:
      (1) Controller returns a <classname>DeferredResult</classname> and saves it
      in some in-memory queue or list where it can be accessed,
      (2) Spring MVC starts async processing, (3) the <classname>DispatcherServlet</classname>
      and all configured Filter's exit the request processing thread but the response
      remains open, (4) the application sets the <classname>DeferredResult</classname>
      from some thread and Spring MVC dispatches the request back to the Servlet container,
      (5) the <classname>DispatcherServlet</classname> is invoked again and processing
      resumes with the asynchronously produced result.
      </para>

      <para>Explaining the motivation for async request processing and when or why to use it
      are beyond the scope of this document. For further information you may wish to read
      <link xl:href="http://blog.springsource.org/2012/05/06/spring-mvc-3-2-preview-introducing-servlet-3-async-support/">this blog post series</link>.
      </para>

      <section xml:id="mvc-ann-async-exceptions">
        <title>Exception Handling for Async Requests</title>

        <para>What happens if a <interfacename>Callable</interfacename> returned
        from a controller method raises an Exception while being executed?
        The effect is similar to what happens when any controller method raises
        an exception. It is handled by a matching
        <interfacename>@ExceptionHandler</interfacename> method in the same
        controller or by one of the configured
        <interfacename>HandlerExceptionResolver</interfacename> instances.</para>

        <note>
          <para>Under the covers, when a <interfacename>Callable</interfacename>
          raises an Exception, Spring MVC still dispatches to the Servlet
          container to resume processing. The only difference is that the
          result of executing the <interfacename>Callable</interfacename>
          is an <classname>Exception</classname> that must be processed
          with the configured
          <interfacename>HandlerExceptionResolver</interfacename> instances.</para>
        </note>

        <para>When using a <classname>DeferredResult</classname>, you have
        a choice of calling its <code>setErrorResult(Object)</code> method
        and provide an <classname>Exception</classname> or any other Object
        you'd like to use as the result. If the result is an
        <classname>Exception</classname>, it will be processed with a
        matching <interfacename>@ExceptionHandler</interfacename> method in the
        same controller or with any configured
        <interfacename>HandlerExceptionResolver</interfacename> instance.</para>
      </section>

      <section xml:id="mvc-ann-async-interception">
        <title>Intercepting Async Requests</title>

        <para>An existing <interfacename>HandlerInterceptor</interfacename> can
        implement <interfacename>AsyncHandlerInterceptor</interfacename>, which
        provides one additional method <code>afterConcurrentHandlingStarted</code>.
        It is invoked after async processing starts and when the initial
        request processing thread is being exited. See the Javadoc of
        <interfacename>AsyncHandlerInterceptor</interfacename> for more details
        on that.</para>

        <para>Further options for async request lifecycle callbacks are
        provided directly on <classname>DeferredResult</classname>,
        which has the methods <code>onTimeout(Runnable)</code> and
        <code>onCompletion(Runnable)</code>. Those are called when the
        async request is about to time out or has completed respectively.
        The timeout event can be handled by setting the
        <classname>DeferredResult</classname> to some value.
        The completion callback however is final and the result can no
        longer be set.</para>

        <para>Similar callbacks are also available with a
        <interfacename>Callable</interfacename>. However, you will need to wrap
        the <interfacename>Callable</interfacename> in an instance of
        <classname>WebAsyncTask</classname> and then use that to register
        the timeout and completion callbacks. Just like with
        <classname>DeferredResult</classname>, the timeout event can be
        handled and a value can be returned while the completion event is final.</para>

        <para>You can also register a
        <interfacename>CallableProcessingInterceptor</interfacename> or a
        <interfacename>DeferredResultProcessingInterceptor</interfacename>
        globally through the MVC Java config or the MVC namespace.
        Those interceptors provide a full set of callbacks and apply every
        time a <interfacename>Callable</interfacename> or a
        <classname>DeferredResult</classname> is used.</para>

      </section>

      <section xml:id="mvc-ann-async-configuration">
        <title>Configuration for Async Request Processing</title>

        <section xml:id="mvc-ann-async-configuration-servlet3">
          <title>Servlet 3 Async Config</title>

          <para>To use Servlet 3 async request processing, you need to update
          <filename>web.xml</filename> to version 3.0:</para>

          <programlisting language="xml">&lt;web-app xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    version="3.0"&gt;

    ...

  &lt;/web-app&gt;
  </programlisting>

          <para>The <classname>DispatcherServlet</classname> and any
          <interfacename>Filter</interfacename> configuration need to have
          the <code>&lt;async-supported&gt;true&lt;/async-supported&gt;</code> sub-element.
          Additionally, any <interfacename>Filter</interfacename> that also needs
          to get involved in async dispatches should also be configured
          to support the ASYNC dispatcher type. Note that it is safe
          to enable the ASYNC dispatcher type for all filters provided with
          the Spring Framework since they will not get involved in async
          dispatches unless needed.</para>

          <para>If using Servlet 3, Java based configuration, e.g. via
          <interfacename>WebApplicationInitializer</interfacename>, you'll
          also need to set the "asyncSupported" flag as well as the
          ASYNC dispatcher type just like with <filename>web.xml</filename>.
          To simplify all this configuration, consider
          extending <classname>AbstractDispatcherServletInitializer</classname>
          or <classname>AbstractAnnotationConfigDispatcherServletInitializer</classname>,
          which automatically set those options and make it very easy to register
          <interfacename>Filter</interfacename> instances.</para>
        </section>

        <section xml:id="mvc-ann-async-configuration-spring-mvc">
          <title>Spring MVC Async Config</title>

          <para>The MVC Java config and the MVC namespace both provide options for
          configuring async request processing.
          <interfacename>WebMvcConfigurer</interfacename> has the method
          <code>configureAsyncSupport</code> while &lt;mvc:annotation-driven&gt;
          has an &lt;async-support&gt; sub-element.</para>

          <para>Those allow you to configure the default timeout value to use for
          async requests, which if not set depends on the underlying Servlet
          container (e.g. 10 seconds on Tomcat). You can also configure an
          <interfacename>AsyncTaskExecutor</interfacename> to use for executing
          <interfacename>Callable</interfacename> instances returned from
          controller methods. It is highly recommended to configure this property
          since by default Spring MVC uses
          <classname>SimpleAsyncTaskExecutor</classname>. The MVC Java config
          and the MVC namespace also allow you to register
          <interfacename>CallableProcessingInterceptor</interfacename> and
          <interfacename>DeferredResultProcessingInterceptor</interfacename>
          instances.</para>

          <para>If you need to override the default timeout value for a
          specific <classname>DeferredResult</classname>, you can do so by using
          the appropriate class constructor. Similarly, for a
          <interfacename>Callable</interfacename>, you can wrap it in a
          <classname>WebAsyncTask</classname> and use the appropriate class
          constructor to customize the timeout value. The class constructor of
          <classname>WebAsyncTask</classname> also allows providing
          an <interfacename>AsyncTaskExecutor</interfacename>.</para>
        </section>

      </section>
    </section>

    <section xml:id="mvc-ann-tests">
      <title>Testing Controllers</title>

      <para>The <filename>spring-test</filename> module offers first class support
      for testing annotated controllers.
      See <xref linkend="spring-mvc-test-framework"/>.</para>
    </section>

  </section>

  <section xml:id="mvc-handlermapping">
    <title>Handler mappings</title>

    <para>In previous versions of Spring, users were required to define one or
    more <interfacename>HandlerMapping</interfacename> beans in the web
    application context to map incoming web requests to appropriate handlers.
    With the introduction of annotated controllers, you generally don't need
    to do that because the <classname>RequestMappingHandlerMapping</classname>
    automatically looks for <interfacename>@RequestMapping</interfacename>
    annotations on all <interfacename>@Controller</interfacename> beans.
    However, do keep in mind that all <classname>HandlerMapping</classname>
    classes extending from <classname>AbstractHandlerMapping</classname> have
    the following properties that you can use to customize their
    behavior:</para>

    <variablelist>
      <varlistentry>
        <term><literal>interceptors</literal></term>

        <listitem>
          <para>List of interceptors to use.
          <interfacename>HandlerInterceptor</interfacename>s are discussed in
          <xref linkend="mvc-handlermapping-interceptor" />.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>defaultHandler</literal></term>

        <listitem>
          <para>Default handler to use, when this handler mapping does not
          result in a matching handler.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>order</literal></term>

        <listitem>
          <para>Based on the value of the order property (see the
          <literal>org.springframework.core.Ordered</literal> interface),
          Spring sorts all handler mappings available in the context and
          applies the first matching handler.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>alwaysUseFullPath</literal></term>

        <listitem>
          <para>If <literal>true</literal> , Spring uses the full path within
          the current Servlet context to find an appropriate handler. If
          <literal>false</literal> (the default), the path within the current
          Servlet mapping is used. For example, if a Servlet is mapped using
          <literal>/testing/*</literal> and the
          <literal>alwaysUseFullPath</literal> property is set to true,
          <literal>/testing/viewPage.html</literal> is used, whereas if the
          property is set to false, <literal>/viewPage.html</literal> is
          used.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><literal>urlDecode</literal></term>

        <listitem>
          <para>Defaults to <literal>true</literal>, as of Spring 2.5. If you
          prefer to compare encoded paths, set this flag to
          <literal>false</literal>. However, the
          <interfacename>HttpServletRequest</interfacename> always exposes the
          Servlet path in decoded form. Be aware that the Servlet path will
          not match when compared with encoded paths.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para>The following example shows how to configure an interceptor:</para>

    <programlisting language="xml">&lt;beans&gt;
  &lt;bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"&gt;
    &lt;property name="interceptors"&gt;
      &lt;bean class="example.MyInterceptor"/&gt;
    &lt;/property&gt;
  &lt;/bean&gt;

&lt;beans&gt;</programlisting>

    <section xml:id="mvc-handlermapping-interceptor">
      <title>Intercepting requests with a
      <interfacename>HandlerInterceptor</interfacename></title>

      <para>Spring's handler mapping mechanism includes handler interceptors,
      which are useful when you want to apply specific functionality to
      certain requests, for example, checking for a principal.</para>

      <para>Interceptors located in the handler mapping must implement
      <interfacename>HandlerInterceptor</interfacename> from the
      <literal>org.springframework.web.servlet</literal> package. This
      interface defines three methods: <literal>preHandle(..)</literal> is
      called <emphasis>before</emphasis> the actual handler is executed;
      <literal>postHandle(..)</literal> is called <emphasis>after</emphasis>
      the handler is executed; and <literal>afterCompletion(..)</literal> is
      called <emphasis>after the complete request has finished</emphasis>.
      These three methods should provide enough flexibility to do all kinds of
      preprocessing and postprocessing.</para>

      <para>The <literal>preHandle(..)</literal> method returns a boolean
      value. You can use this method to break or continue the processing of
      the execution chain. When this method returns <literal>true</literal>,
      the handler execution chain will continue; when it returns false, the
      <classname>DispatcherServlet</classname> assumes the interceptor itself
      has taken care of requests (and, for example, rendered an appropriate
      view) and does not continue executing the other interceptors and the
      actual handler in the execution chain.</para>

      <para>Interceptors can be configured using the
      <literal>interceptors</literal> property, which is present on all
      <classname>HandlerMapping</classname> classes extending from
      <classname>AbstractHandlerMapping</classname>. This is shown in the
      example below:</para>

      <programlisting language="xml">&lt;beans&gt;
    &lt;bean id="handlerMapping"
          class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"&gt;
        &lt;property name="interceptors"&gt;
            &lt;list&gt;
                &lt;ref bean="officeHoursInterceptor"/&gt;
            &lt;/list&gt;
        &lt;/property&gt;
    &lt;/bean&gt;

    &lt;bean id="officeHoursInterceptor"
          class="samples.TimeBasedAccessInterceptor"&gt;
        &lt;property name="openingTime" value="9"/&gt;
        &lt;property name="closingTime" value="18"/&gt;
    &lt;/bean&gt;
&lt;beans&gt;</programlisting>

      <programlisting language="java">package samples;

public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter {

    private int openingTime;
    private int closingTime;

    public void setOpeningTime(int openingTime) {
        this.openingTime = openingTime;
    }

    public void setClosingTime(int closingTime) {
        this.closingTime = closingTime;
    }

    public boolean preHandle(
            HttpServletRequest request,
            HttpServletResponse response,
            Object handler) throws Exception {

        Calendar cal = Calendar.getInstance();
        int hour = cal.get(HOUR_OF_DAY);
        if (openingTime &lt;= hour &amp;&amp; hour &lt; closingTime) {
            return true;
        } else {
            response.sendRedirect("http://host.com/outsideOfficeHours.html");
            return false;
        }
    }
}</programlisting>

      <para>Any request handled by this mapping is intercepted by the
      <classname>TimeBasedAccessInterceptor</classname>. If the current time
      is outside office hours, the user is redirected to a static HTML file
      that says, for example, you can only access the website during office
      hours.</para>

      <note>
        <para>When using the
        <classname>RequestMappingHandlerMapping</classname> the actual handler
        is an instance of <classname>HandlerMethod</classname> which
        identifies the specific controller method that will be invoked.</para>
      </note>

      <para>As you can see, the Spring adapter class
      <classname>HandlerInterceptorAdapter</classname> makes it easier to
      extend the <interfacename>HandlerInterceptor</interfacename>
      interface.</para>

      <tip>
        <para>In the example above, the configured interceptor will apply to
        all requests handled with annotated controller methods. If you want to
        narrow down the URL paths to which an interceptor applies, you can use
        the MVC namespace or the MVC Java config, or declare bean instances
        of type <classname>MappedInterceptor</classname> to do that. See <link
        linkend="mvc-config-enable">Enabling the MVC Java Config or the MVC
        XML Namespace</link>.</para>
      </tip>
    </section>
  </section>

  <section xml:id="mvc-viewresolver">
    <title>Resolving views</title>

    <para>All MVC frameworks for web applications provide a way to address
    views. Spring provides view resolvers, which enable you to render models
    in a browser without tying you to a specific view technology. Out of the
    box, Spring enables you to use JSPs, Velocity templates and XSLT views,
    for example. See <xref linkend="view" /> for a discussion of how to
    integrate and use a number of disparate view technologies.</para>

    <para>The two interfaces that are important to the way Spring handles
    views are <interfacename>ViewResolver</interfacename> and
    <interfacename>View</interfacename>. The
    <interfacename>ViewResolver</interfacename> provides a mapping between
    view names and actual views. The <interfacename>View</interfacename>
    interface addresses the preparation of the request and hands the request
    over to one of the view technologies.</para>

    <section xml:id="mvc-viewresolver-resolver">
      <title>Resolving views with the
      <interfacename>ViewResolver</interfacename> interface</title>

      <para>As discussed in <xref linkend="mvc-controller" />, all handler
      methods in the Spring Web MVC controllers must resolve to a logical view
      name, either explicitly (e.g., by returning a <literal>String</literal>,
      <literal>View</literal>, or <literal>ModelAndView</literal>) or
      implicitly (i.e., based on conventions). Views in Spring are addressed
      by a logical view name and are resolved by a view resolver. Spring comes
      with quite a few view resolvers. This table lists most of them; a couple
      of examples follow.</para>

      <table xml:id="mvc-view-resolvers-tbl">
        <title>View resolvers</title>

        <tgroup cols="2">
          <colspec colname="c1" colwidth="1*" />

          <colspec colname="c2" colwidth="2*" />

          <thead>
            <row>
              <entry><interfacename>ViewResolver</interfacename></entry>

              <entry>Description</entry>
            </row>
          </thead>

          <tbody>
            <row>
              <entry><classname>AbstractCachingViewResolver</classname></entry>

              <entry>Abstract view resolver that caches views. Often views
              need preparation before they can be used; extending this view
              resolver provides caching.</entry>
            </row>

            <row>
              <entry><classname>XmlViewResolver</classname></entry>

              <entry>Implementation of
              <interfacename>ViewResolver</interfacename> that accepts a
              configuration file written in XML with the same DTD as Spring's
              XML bean factories. The default configuration file is
              <literal>/WEB-INF/views.xml</literal>.</entry>
            </row>

            <row>
              <entry><classname>ResourceBundleViewResolver</classname></entry>

              <entry>Implementation of
              <interfacename>ViewResolver</interfacename> that uses bean
              definitions in a <classname>ResourceBundle</classname>,
              specified by the bundle base name. Typically you define the
              bundle in a properties file, located in the classpath. <!--Correct to say you define? Seems so, because default implies you can change it.-->The
              default file name is
              <literal>views.properties</literal>.</entry>
            </row>

            <row>
              <entry><classname>UrlBasedViewResolver</classname></entry>

              <entry>Simple implementation of the
              <interfacename>ViewResolver</interfacename> interface that
              effects the direct resolution of logical view names to URLs,
              without an explicit mapping definition. This is appropriate if
              your logical names match the names of your view resources in a
              straightforward manner, without the need for arbitrary
              mappings.</entry>
            </row>

            <row>
              <entry><classname>InternalResourceViewResolver</classname></entry>

              <entry>Convenient subclass of
              <classname>UrlBasedViewResolver</classname> that supports
              <classname>InternalResourceView</classname> (in effect, Servlets
              and JSPs) and subclasses such as <classname>JstlView</classname>
              and <classname>TilesView</classname>. You can specify the view
              class for all views generated by this resolver by using
              <literal>setViewClass(..)</literal>. See the Javadocs for the
              <classname>UrlBasedViewResolver</classname> class for
              details.</entry>
            </row>

            <row>
              <entry><classname>VelocityViewResolver</classname> /
              <classname>FreeMarkerViewResolver</classname></entry>

              <entry>Convenient subclass of
              <classname>UrlBasedViewResolver</classname> that supports
              <classname>VelocityView</classname> (in effect, Velocity
              templates) or <classname>FreeMarkerView</classname>
              ,respectively, and custom subclasses of them.</entry>
            </row>

            <row>
              <entry><classname>ContentNegotiatingViewResolver</classname></entry>

              <entry>Implementation of the
              <interfacename>ViewResolver</interfacename> interface that
              resolves a view based on the request file name or
              <literal>Accept</literal> header. See <xref
              linkend="mvc-multiple-representations" />.</entry>
            </row>
          </tbody>
        </tgroup>
      </table>

      <para>As an example, with JSP as a view technology, you can use the
      <classname>UrlBasedViewResolver</classname>. This view resolver
      translates a view name to a URL and hands the request over to the
      RequestDispatcher to render the view.</para>

      <programlisting language="xml">&lt;bean id="viewResolver"
      class="org.springframework.web.servlet.view.UrlBasedViewResolver"&gt;
    &lt;property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/&gt;
    &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
    &lt;property name="suffix" value=".jsp"/&gt;
&lt;/bean&gt;</programlisting>

      <para>When returning <literal>test</literal> as a logical view name,
      this view resolver forwards the request to the
      <classname>RequestDispatcher</classname> that will send the request to
      <literal>/WEB-INF/jsp/test.jsp</literal>.</para>

      <para>When you combine different view technologies in a web application,
      you can use the
      <classname>ResourceBundleViewResolver</classname>:</para>

      <programlisting language="xml">&lt;bean id="viewResolver"
      class="org.springframework.web.servlet.view.ResourceBundleViewResolver"&gt;
    &lt;property name="basename" value="views"/&gt;
    &lt;property name="defaultParentView" value="parentView"/&gt;
&lt;/bean&gt;</programlisting>

      <para>The <classname>ResourceBundleViewResolver</classname> inspects the
      <classname>ResourceBundle</classname> identified by the basename, and
      for each view it is supposed to resolve, it uses the value of the
      property <literal>[viewname].(class)</literal> as the view class and the
      value of the property <literal>[viewname].url</literal> as the view url.
      Examples can be found in the next chapter which covers view
      technologies. As you can see, you can identify a parent view, from which
      all views in the properties file <quote>extend</quote>. This way you can
      specify a default view class, for example.</para>

      <note>
        <para>Subclasses of <classname>AbstractCachingViewResolver</classname>
        cache view instances that they resolve. Caching improves performance
        of certain view technologies. It's possible to turn off the cache by
        setting the <literal>cache</literal> property to
        <literal>false</literal>. Furthermore, if you must refresh a certain
        view at runtime (for example when a Velocity template is modified),
        you can use the <literal>removeFromCache(String viewName, Locale
        loc)</literal> method.</para>
      </note>
    </section>

    <section xml:id="mvc-viewresolver-chaining">
      <title>Chaining ViewResolvers</title>

      <para>Spring supports multiple view resolvers. Thus you can chain
      resolvers and, for example, override specific views in certain
      circumstances. You chain view resolvers by adding more than one resolver
      to your application context and, if necessary, by setting the
      <literal>order</literal> property to specify ordering. Remember, the
      higher the order property, the later the view resolver is positioned in
      the chain.</para>

      <para>In the following example, the chain of view resolvers consists of
      two resolvers, an <classname>InternalResourceViewResolver</classname>,
      which is always automatically positioned as the last resolver in the
      chain, and an <classname>XmlViewResolver</classname> for specifying
      Excel views. Excel views are not supported by the
      <classname>InternalResourceViewResolver</classname>.<!--Do you need to say anything else about excel not being supported by one of resolvers? What if anything is the result?--></para>

      <programlisting language="xml">&lt;bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"&gt;
  &lt;property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/&gt;
  &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
  &lt;property name="suffix" value=".jsp"/&gt;
&lt;/bean&gt;

&lt;bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver"&gt;
  &lt;property name="order" value="1"/&gt;
  &lt;property name="location" value="/WEB-INF/views.xml"/&gt;
&lt;/bean&gt;

<lineannotation>&lt;!-- in views.xml --&gt;</lineannotation>

&lt;beans&gt;
  &lt;bean name="report" class="org.springframework.example.ReportExcelView"/&gt;
&lt;/beans&gt;</programlisting>

      <para>If a specific view resolver does not result in a view, Spring
      examines the context for other view resolvers. If additional view
      resolvers exist, Spring continues to inspect them until a view is
      resolved. If no view resolver returns a view, Spring throws a
      <classname>ServletException</classname>.</para>

      <para>The contract of a view resolver specifies that a view resolver
      <emphasis>can</emphasis> return null to indicate the view could not be
      found. Not all view resolvers do this, however, because in some cases,
      the resolver simply cannot detect whether or not the view exists. For
      example, the <classname>InternalResourceViewResolver</classname> uses
      the <classname>RequestDispatcher</classname> internally, and dispatching
      is the only way to figure out if a JSP exists, but this action can only
      execute once. The same holds for the
      <classname>VelocityViewResolver</classname> and some others. Check the
      Javadoc for the view resolver to see whether it reports non-existing
      views. Thus, putting an
      <classname>InternalResourceViewResolver</classname> in the chain in a
      place other than the last, results in the chain not being fully
      inspected, because the
      <classname>InternalResourceViewResolver</classname> will
      <emphasis>always</emphasis> return a view!<!--I don't understand the logic of this. How can it return a view if no view exists or no view can be found? this paragraph is confusing.--><!--Why would you put InternalResourceViewResolver in place other than last? It's automatically last. --></para>
    </section>

    <section xml:id="mvc-redirecting">
      <title>Redirecting to views<!--Revise to say what you are redirecting to views. OR are you redirecting views? In that case heading should be Redirecting views.--></title>

      <para>As mentioned previously, a controller typically returns a logical
      view name, which a view resolver resolves to a particular view
      technology. For view technologies such as JSPs that are processed
      through the Servlet or JSP engine, this resolution is usually handled
      through the combination of
      <classname>InternalResourceViewResolver</classname> and
      <classname>InternalResourceView</classname>, which issues an internal
      forward or include via the Servlet API's
      <literal>RequestDispatcher.forward(..)</literal> method or
      <literal>RequestDispatcher.include()</literal> method. For other view
      technologies, such as Velocity, XSLT, and so on, the view itself writes
      the content directly to the response stream.</para>

      <para>It is sometimes desirable to issue an HTTP redirect back to the
      client, before the view is rendered. This is desirable, for example,
      when one controller has been called with <literal>POST</literal>ed data,
      and the response is actually a delegation to another controller (for
      example on a successful form submission). In this case, a normal
      internal forward will mean that the other controller will also see the
      same <literal>POST</literal> data, which is potentially problematic if
      it can confuse it with other expected data. Another reason to perform a
      redirect before displaying the result is to eliminate the possibility of
      the user submitting the form data multiple times. In this scenario, the
      browser will first send an initial <literal>POST</literal>; it will then
      receive a response to redirect to a different URL; and finally the
      browser will perform a subsequent <literal>GET</literal> for the URL
      named in the redirect response. Thus, from the perspective of the
      browser, the current page does not reflect the result of a
      <literal>POST</literal> but rather of a <literal>GET</literal>. The end
      effect is that there is no way the user can accidentally
      re-<literal>POST</literal> the same data by performing a refresh. The
      refresh forces a <literal>GET</literal> of the result page, not a resend
      of the initial <literal>POST</literal> data.</para>

      <section xml:id="mvc-redirecting-redirect-view">
        <title><classname>RedirectView</classname></title>

        <para>One way to force a redirect as the result of a controller
        response is for the controller to create and return an instance of
        Spring's <classname>RedirectView</classname>. In this case,
        <classname>DispatcherServlet</classname> does not use the normal view
        resolution mechanism. Rather because it has been given the (redirect)
        view already, the <classname>DispatcherServlet</classname> simply
        instructs the view to do its work.</para>

        <para>The <classname>RedirectView</classname> issues an
        <literal>HttpServletResponse.sendRedirect()</literal> call that
        returns to the client browser as an HTTP redirect. By default all
        model attributes are considered to be exposed as URI template
        variables in the redirect URL. Of the remaining attributes those that
        are primitive types or collections/arrays of primitive types are
        automatically appended as query parameters.</para>

        <para>Appending primitive type attributes as query parameters may be
        the desired result if a model instance was prepared specifically for
        the redirect. However, in annotated controllers the model may contain
        additional attributes added for rendering purposes (e.g. drop-down
        field values). To avoid the possibility of having such attributes
        appear in the URL an annotated controller can declare an argument of
        type <interfacename>RedirectAttributes</interfacename> and use it to
        specify the exact attributes to make available to
        <classname>RedirectView</classname>. If the controller method decides
        to redirect, the content of
        <interfacename>RedirectAttributes</interfacename> is used. Otherwise
        the content of the model is used.</para>

        <para>Note that URI template variables from the present request are
        automatically made available when expanding a redirect URL and do not
        need to be added explicitly neither through
        <interfacename>Model</interfacename> nor
        <interfacename>RedirectAttributes</interfacename>. For example:</para>

        <programlisting language="java">@RequestMapping(value = "/files/{path}", method = RequestMethod.POST)
public String upload(...) {
    // ...
    return "redirect:files/{path}";
}</programlisting>

        <para>If you use <classname>RedirectView</classname> and the view is
        created by the controller itself, it is recommended that you configure
        the redirect URL to be injected into the controller so that it is not
        baked into the controller but configured in the context along with the
        view names. The next section discusses this process.</para>
      </section>

      <section xml:id="mvc-redirecting-redirect-prefix">
        <title>The <literal>redirect:</literal> prefix</title>

        <para>While the use of <classname>RedirectView</classname> works fine,
        if the controller itself creates the
        <classname>RedirectView</classname>, there is no avoiding the fact
        that the controller is aware that a redirection is happening. This is
        really suboptimal and couples things too tightly. The controller
        should not really care about how the response gets handled. In general
        it should operate only in terms of view names that have been injected
        into it.</para>

        <para>The special <literal>redirect:</literal> prefix allows you to
        accomplish this. If a view name is returned that has the prefix
        <literal>redirect:</literal>, the
        <classname>UrlBasedViewResolver</classname> (and all subclasses) will
        recognize this as a special indication that a redirect is needed. The
        rest of the view name will be treated as the redirect URL.</para>

        <para>The net effect is the same as if the controller had returned a
        <classname>RedirectView</classname>, but now the controller itself can
        simply operate in terms of logical view names. A logical view name
        such as <literal>redirect:/myapp/some/resource</literal> will redirect
        relative to the current Servlet context, while a name such as
        <literal>redirect:http://myhost.com/some/arbitrary/path</literal> will
        redirect to an absolute URL.</para>
      </section>

      <section xml:id="mvc-redirecting-forward-prefix">
        <title>The <literal>forward:</literal> prefix<!--Can you revise this heading to say what you're using the forward prefix to accomplish?--></title>

        <para>It is also possible to use a special <literal>forward:</literal>
        prefix for view names that are ultimately resolved by
        <classname>UrlBasedViewResolver</classname> and subclasses. This
        creates an <classname>InternalResourceView</classname> (which
        ultimately does a <literal>RequestDispatcher.forward()</literal>)
        around the rest of the view name, which is considered a URL.
        Therefore, this prefix is not useful with
        <classname>InternalResourceViewResolver</classname> and
        <classname>InternalResourceView</classname> (for JSPs for example).
        But the prefix can be helpful when you are primarily using another
        view technology, but still want to force a forward of a resource to be
        handled by the Servlet/JSP engine. (Note that you may also chain
        multiple view resolvers, instead.)<!--I think the preceding sentences were a bit garbled. I tried to reword a bit. And is this paragraph logical?--></para>

        <para>As with the <literal>redirect:</literal> prefix, if the view
        name with the <literal>forward:</literal> prefix is injected into the
        controller, the controller does not detect that anything special is
        happening in terms of handling the response.<!--Can you reword to clarify the point? The controller does not detect what?--></para>
      </section>
    </section>

    <section xml:id="mvc-multiple-representations">
      <title><classname>ContentNegotiatingViewResolver</classname></title>

      <para>The <classname>ContentNegotiatingViewResolver</classname> does not
      resolve views itself but rather delegates to other view resolvers,
      selecting the view that resembles the representation requested by the
      client. Two strategies exist for a client to request a representation
      from the server:</para>

      <itemizedlist>
        <listitem>
          <para>Use a distinct URI for each resource, typically by using a
          different file extension in the URI. For example, the URI<literal>
          http://www.example.com/users/fred.pdf</literal> requests a PDF
          representation of the user fred, and
          <literal>http://www.example.com/users/fred.xml</literal> requests an
          XML representation.</para>
        </listitem>
      </itemizedlist>

      <itemizedlist>
        <listitem>
          <para>Use the same URI for the client to locate the resource, but
          set the <literal>Accept</literal> HTTP request header to list the
          <link xl:href="http://en.wikipedia.org/wiki/Internet_media_type">media
          types</link> that it understands. For example, an HTTP request for
          <literal>http://www.example.com/users/fred</literal> with an
          <literal>Accept</literal> header set to <literal>application/pdf
          </literal>requests a PDF representation of the user fred, while
          <literal>http://www.example.com/users/fred</literal> with an
          <literal>Accept</literal> header set to <literal>text/xml</literal>
          requests an XML representation. This strategy is known as <link
          xl:href="http://en.wikipedia.org/wiki/Content_negotiation">content
          negotiation</link>.</para>
        </listitem>
      </itemizedlist>

      <note>
        <para>One issue with the <literal>Accept</literal> header is that it
        is impossible to set it in a web browser within HTML. For example, in
        Firefox, it is fixed to:<!--So how would you set the Accept header as in second bullet, if you can't do it in html? Indicate?--></para>

        <programlisting>Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8</programlisting>

        <para>For this reason it is common to see the use of a distinct URI
        for each representation when developing browser based web
        applications.</para>
      </note>

      <para>To support multiple representations of a resource, Spring provides
      the <classname>ContentNegotiatingViewResolver</classname> to resolve a
      view based on the file extension or <literal>Accept</literal> header of
      the HTTP request. <classname>ContentNegotiatingViewResolver</classname>
      does not perform the view resolution itself but instead delegates to a
      list of view resolvers that you specify through the bean property
      <literal>ViewResolvers</literal>.<!--A human has to specify this list of resolvers, right? See example below.--></para>

      <para>The <classname>ContentNegotiatingViewResolver</classname> selects
      an appropriate <classname>View</classname> to handle the request by
      comparing the request media type(s) with the media type (also known as
      <literal>Content-Type</literal>) supported by the
      <classname>View</classname> associated with each of its
      <classname>ViewResolvers</classname>. The first
      <classname>View</classname> in the list that has a compatible
      <literal>Content-Type</literal> returns the representation to the
      client. If a compatible view cannot be supplied by the
      <classname>ViewResolver</classname> chain, then the list of views
      specified through the <literal>DefaultViews</literal> property will be
      consulted. This latter option is appropriate for singleton
      <classname>Views</classname> that can render an appropriate
      representation of the current resource regardless of the logical view
      name. The <literal>Accept</literal> header may include wild cards, for
      example <literal>text/*</literal>, in which case a
      <classname>View</classname> whose Content-Type was
      <literal>text/xml</literal> is a compatible match.</para>

      <para>To support the resolution of a view based on a file extension, use
      the <classname>ContentNegotiatingViewResolver </classname>bean property
      <literal>mediaTypes</literal> to specify a mapping of file extensions to
      media types. For more information on the algorithm used to determine the
      request media type, refer to the API documentation for
      <classname>ContentNegotiatingViewResolver</classname>.</para>

      <para>Here is an example configuration of a
      <classname>ContentNegotiatingViewResolver:</classname></para>

      <programlisting language="xml">&lt;bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver"&gt;
  &lt;property name="mediaTypes"&gt;
    &lt;map&gt;
      &lt;entry key="atom" value="application/atom+xml"/&gt;
      &lt;entry key="html" value="text/html"/&gt;
      &lt;entry key="json" value="application/json"/&gt;
    &lt;/map&gt;
  &lt;/property&gt;
  &lt;property name="viewResolvers"&gt;
    &lt;list&gt;
      &lt;bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/&gt;
      &lt;bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"&gt;
        &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
        &lt;property name="suffix" value=".jsp"/&gt;
      &lt;/bean&gt;
    &lt;/list&gt;
  &lt;/property&gt;
  &lt;property name="defaultViews"&gt;
    &lt;list&gt;
      &lt;bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView" /&gt;
    &lt;/list&gt;
  &lt;/property&gt;
&lt;/bean&gt;


&lt;bean id="content" class="com.springsource.samples.rest.SampleContentAtomView"/&gt;</programlisting>

      <para>The <classname>InternalResourceViewResolver</classname> handles
      the translation of view names and JSP pages, while the
      <classname>BeanNameViewResolver</classname> returns a view based on the
      name of a bean. (See "<link
      linkend="mvc-viewresolver-resolver">Resolving views with the
      ViewResolver interface</link>" for more details on how Spring looks up
      and instantiates a view.) In this example, the
      <literal>content</literal> bean is a class that inherits from
      <classname>AbstractAtomFeedView</classname>, which returns an Atom RSS
      feed. For more information on creating an Atom Feed representation, see
      the section Atom Views.<!--Need a correct link or x-ref re the preceding sentence.I couldn't find an "Atom Views" section.--></para>

      <para>In the above configuration, if a request is made with an
      <literal>.html</literal> extension, the view resolver looks for a view
      that matches the <literal>text/html</literal> media type. The
      <classname>InternalResourceViewResolver</classname> provides the
      matching view for <literal>text/html</literal>. If the request is made
      with the file extension <literal>.atom</literal>, the view resolver
      looks for a view that matches the
      <literal>application/atom+xml</literal> media type. This view is
      provided by the <classname>BeanNameViewResolver</classname> that maps to
      the <classname>SampleContentAtomView</classname> if the view name
      returned is <classname>content</classname>. If the request is made with
      the file extension <literal>.json</literal>, the
      <classname>MappingJackson2JsonView</classname>instance from the
      <literal>DefaultViews</literal> list will be selected regardless of the
      view name. Alternatively, client requests can be made without a file
      extension but with the <literal>Accept</literal> header set to the
      preferred media-type, and the same resolution of request to views would
      occur.<!--Can you reword preceding sentence? I don't follow it.--></para>

      <note>
        <para>If <classname>ContentNegotiatingViewResolver</classname>'s list
        of ViewResolvers is not configured explicitly, it automatically uses
        any ViewResolvers defined in the application context.</para>
      </note>

      <para>The corresponding controller code that returns an Atom RSS feed
      for a URI of the form <literal>http://localhost/content.atom</literal>
      or <literal>http://localhost/content</literal> with an
      <literal>Accept</literal> header of application/atom+xml is shown
      below.</para>

      <programlisting language="java">@Controller
public class ContentController {

    private List&lt;SampleContent&gt; contentList = new ArrayList&lt;SampleContent&gt;();

    @RequestMapping(value="/content", method=RequestMethod.GET)
    public ModelAndView getContent() {
        ModelAndView mav = new ModelAndView();
        mav.setViewName("content");
        mav.addObject("sampleContentList", contentList);
        return mav;
    }

}</programlisting>
    </section>
  </section>

  <section xml:id="mvc-flash-attributes">
    <title>Using flash attributes</title>

    <para>Flash attributes provide a way for one request to store attributes
    intended for use in another. This is most commonly needed when redirecting
    — for example, the <emphasis>Post/Redirect/Get</emphasis> pattern. Flash
    attributes are saved temporarily before the redirect (typically in the
    session) to be made available to the request after the redirect and
    removed immediately.</para>

    <para>Spring MVC has two main abstractions in support of flash attributes.
    <classname>FlashMap</classname> is used to hold flash attributes while
    <interfacename>FlashMapManager</interfacename> is used to store, retrieve,
    and manage <classname>FlashMap</classname> instances.</para>

    <para>Flash attribute support is always "on" and does not need to enabled
    explicitly although if not used, it never causes HTTP session creation. On
    each request there is an "input" <classname>FlashMap</classname> with
    attributes passed from a previous request (if any) and an "output"
    <classname>FlashMap</classname> with attributes to save for a subsequent
    request. Both <classname>FlashMap</classname> instances are accessible
    from anywhere in Spring MVC through static methods in
    <classname>RequestContextUtils</classname>.</para>

    <para>Annotated controllers typically do not need to work with
    <classname>FlashMap</classname> directly. Instead an
    <interfacename>@RequestMapping</interfacename> method can accept an
    argument of type <interfacename>RedirectAttributes</interfacename> and use
    it to add flash attributes for a redirect scenario. Flash attributes added
    via <interfacename>RedirectAttributes</interfacename> are automatically
    propagated to the "output" FlashMap. Similarly after the redirect
    attributes from the "input" <classname>FlashMap</classname> are
    automatically added to the <interfacename>Model</interfacename> of the
    controller serving the target URL.</para>

    <sidebar xml:id="mvc-flash-attributes-concurrency">
      <title>Matching requests to flash attributes</title>

      <para>The concept of flash attributes exists in many other Web
      frameworks and has proven to be exposed sometimes to concurrency issues.
      This is because by definition flash attributes are to be stored until
      the next request. However the very "next" request may not be the
      intended recipient but another asynchronous request (e.g. polling or
      resource requests) in which case the flash attributes are removed too
      early.</para>

      <para>To reduce the possibility of such issues,
      <classname>RedirectView</classname> automatically "stamps"
      <classname>FlashMap</classname> instances with the path and query
      parameters of the target redirect URL. In turn the default
      <classname>FlashMapManager</classname> matches that information to
      incoming requests when looking up the "input"
      <classname>FlashMap</classname>.</para>

      <para>This does not eliminate the possibility of a concurrency issue
      entirely but nevertheless reduces it greatly with information that is
      already available in the redirect URL. Therefore the use of flash
      attributes is recommended mainly for redirect scenarios .</para>
    </sidebar>
  </section>

  <section xml:id="mvc-construct-encode-uri">
    <title>Building <literal>URI</literal>s</title>

    <para>Spring MVC provides a mechanism for building and encoding a URI
    using <classname>UriComponentsBuilder</classname> and
    <classname>UriComponents</classname>.
    </para>

    <para>For example you can expand and encode a URI template string:</para>

<programlisting language="java">UriComponents uriComponents =
        UriComponentsBuilder.fromUriString("http://example.com/hotels/{hotel}/bookings/{booking}").build();

URI uri = uriComponents.expand("42", "21").encode().toUri();
</programlisting>

    <para>Note that <classname>UriComponents</classname> is immutable and
    the <literal>expand()</literal> and <literal>encode()</literal>
    operations return new instances if necessary.</para>

    <para>You can also expand and encode using individual URI components:</para>

<programlisting language="java">UriComponents uriComponents =
        UriComponentsBuilder.newInstance()
            .scheme("http").host("example.com").path("/hotels/{hotel}/bookings/{booking}").build()
            .expand("42", "21")
            .encode();
</programlisting>

    <para>In a Servlet environment the
    <classname>ServletUriComponentsBuilder</classname> sub-class provides
    static factory methods to copy available URL information from a
    Servlet requests:
    </para>

<programlisting language="java">HttpServletRequest request = ...

// Re-use host, scheme, port, path and query string
// Replace the "accountId" query param

ServletUriComponentsBuilder ucb =
        ServletUriComponentsBuilder.fromRequest(request).replaceQueryParam("accountId", "{id}").build()
            .expand("123")
            .encode();
</programlisting>

    <para>Alternatively, you may choose to copy a subset of the available
    information up to and including the context path:</para>

<programlisting language="java">// Re-use host, port and context path
// Append "/accounts" to the path

ServletUriComponentsBuilder ucb =
        ServletUriComponentsBuilder.fromContextPath(request).path("/accounts").build()
</programlisting>

    <para>Or in cases where the <classname>DispatcherServlet</classname> is mapped
    by name (e.g. <literal>/main/*</literal>), you can also have the literal part
    of the servlet mapping included:</para>

<programlisting language="java">// Re-use host, port, context path
// Append the literal part of the servlet mapping to the path
// Append "/accounts" to the path

ServletUriComponentsBuilder ucb =
        ServletUriComponentsBuilder.fromServletMapping(request).path("/accounts").build()
</programlisting>

  </section>

  <section xml:id="mvc-localeresolver">
    <title>Using locales</title>

    <para>Most parts of Spring's architecture support internationalization,
    just as the Spring web MVC framework does.
    <classname>DispatcherServlet</classname> enables you to automatically
    resolve messages using the client's locale. This is done with
    <interfacename>LocaleResolver</interfacename> objects.</para>

    <para>When a request comes in, the
    <classname>DispatcherServlet</classname> looks for a locale resolver, and
    if it finds one it tries to use it to set the locale. Using the
    <literal>RequestContext.getLocale()</literal> method, you can always
    retrieve the locale that was resolved by the locale resolver.</para>

    <para>In addition to automatic locale resolution, you can also attach an
    interceptor to the handler mapping (see <xref
    linkend="mvc-handlermapping-interceptor" /> for more information on
    handler mapping interceptors) to change the locale under specific
    circumstances, for example, based on a parameter in the request.</para>

    <para>Locale resolvers and interceptors are defined in the
    <literal>org.springframework.web.servlet.i18n</literal> package and are
    configured in your application context in the normal way. Here is a
    selection of the locale resolvers included in Spring.</para>

    <section xml:id="mvc-localeresolver-acceptheader">
      <title><classname>AcceptHeaderLocaleResolver</classname></title>

      <para>This locale resolver inspects the
      <literal>accept-language</literal> header in the request that was sent
      by the client (e.g., a web browser). Usually this header field contains
      the locale of the client's operating system.</para>
    </section>

    <section xml:id="mvc-localeresolver-cookie">
      <title><classname>CookieLocaleResolver</classname></title>

      <para>This locale resolver inspects a <classname>Cookie</classname> that
      might exist on the client to see if a locale is specified. If so, it
      uses the specified locale. Using the properties of this locale resolver,
      you can specify the name of the cookie as well as the maximum age. Find
      below an example of defining a
      <classname>CookieLocaleResolver</classname>.</para>

      <programlisting language="xml">&lt;bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"&gt;

    &lt;property name="cookieName" value="clientlanguage"/&gt;

    <lineannotation>&lt;!-- in seconds. If set to -1, the cookie is not persisted (deleted when browser shuts down) --&gt;</lineannotation>
    &lt;property name="cookieMaxAge" value="100000"&gt;

&lt;/bean&gt;</programlisting>

      <table xml:id="mvc-cookie-locale-resolver-props-tbl">
        <title><classname>CookieLocaleResolver</classname> properties</title>

        <tgroup cols="3">
          <colspec colname="c1" colwidth="1*" />

          <colspec colname="c2" colwidth="1*" />

          <colspec colname="c3" colwidth="3*" />

          <thead>
            <row>
              <entry>Property</entry>

              <entry>Default</entry>

              <entry>Description</entry>
            </row>
          </thead>

          <tbody>
            <row>
              <entry>cookieName</entry>

              <entry>classname + LOCALE</entry>

              <entry>The name of the cookie</entry>
            </row>

            <row>
              <entry>cookieMaxAge</entry>

              <entry>Integer.MAX_INT</entry>

              <entry>The maximum time a cookie will stay persistent on the
              client. If -1 is specified, the cookie will not be persisted; it
              will only be available until the client shuts down his or her
              browser.</entry>
            </row>

            <row>
              <entry>cookiePath</entry>

              <entry>/</entry>

              <entry>Limits the visibility of the cookie to a certain part of
              your site. When cookiePath is specified, the cookie will only be
              visible to that path and the paths below it.</entry>
            </row>
          </tbody>
        </tgroup>
      </table>
    </section>

    <section xml:id="mvc-localeresolver-session">
      <title><classname>SessionLocaleResolver</classname></title>

      <para>The <classname>SessionLocaleResolver</classname> allows you to
      retrieve locales from the session that might be associated with the
      user's request.<!--Aren't you missing some information and example? This section has only one sentence.--></para>
    </section>

    <section xml:id="mvc-localeresolver-interceptor">
      <title><classname>LocaleChangeInterceptor</classname></title>

      <para>You can enable changing of locales by adding the
      <classname>LocaleChangeInterceptor</classname> to one of the handler
      mappings (see <xref linkend="mvc-handlermapping" />). It will detect a
      parameter in the request and change the locale. It calls
      <literal>setLocale()</literal> on the
      <interfacename>LocaleResolver</interfacename> that also exists in the
      context. The following example shows that calls to all
      <literal>*.view</literal> resources containing a parameter named
      <literal>siteLanguage</literal> will now change the locale. So, for
      example, a request for the following URL,
      <literal>http://www.sf.net/home.view?siteLanguage=nl</literal> will
      change the site language to Dutch.</para>

      <programlisting language="xml">&lt;bean id="localeChangeInterceptor"
      class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"&gt;
    &lt;property name="paramName" value="siteLanguage"/&gt;
&lt;/bean&gt;

&lt;bean id="localeResolver"
      class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/&gt;

&lt;bean id="urlMapping"
      class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"&gt;
    &lt;property name="interceptors"&gt;
        &lt;list&gt;
            &lt;ref bean="localeChangeInterceptor"/&gt;
        &lt;/list&gt;
    &lt;/property&gt;
    &lt;property name="mappings"&gt;
        &lt;value&gt;/**/*.view=someController&lt;/value&gt;
    &lt;/property&gt;
&lt;/bean&gt;</programlisting>
    </section>
  </section>

  <section xml:id="mvc-themeresolver">
    <title>Using themes</title>

    <section xml:id="mvc-themeresolver-introduction">
      <title>Overview of themes</title>

      <para>You can apply Spring Web MVC framework themes to set the overall
      look-and-feel of your application, thereby enhancing user experience. A
      theme is a collection of static resources, typically style sheets and
      images, that affect the visual style of the application.</para>
    </section>

    <section xml:id="mvc-themeresolver-defining">
      <title>Defining themes</title>

      <para>To use themes in your web application, you must set up an
      implementation of the
      <interfacename>org.springframework.ui.context.ThemeSource</interfacename>
      interface. The <interfacename>WebApplicationContext</interfacename>
      interface extends <interfacename>ThemeSource</interfacename> but
      delegates its responsibilities to a dedicated implementation. By default
      the delegate will be an
      <classname>org.springframework.ui.context.support.ResourceBundleThemeSource</classname>
      implementation that loads properties files from the root of the
      classpath. To use a custom <interfacename>ThemeSource</interfacename>
      implementation or to configure the base name prefix of the
      <classname>ResourceBundleThemeSource</classname>, you can register a
      bean in the application context with the reserved name
      <classname>themeSource</classname>. The web application context
      automatically detects a bean with that name and uses it.</para>

      <para>When using the <classname>ResourceBundleThemeSource</classname>, a
      theme is defined in a simple properties file. <!--Revise preceding sentence to clarify: To use ResourceBundleThemeSource, you define a theme in a properties file? OR do you mean a theme--><!--is already defined in a simple properties file for use with ResourceBundleThemeSource?-->The
      properties file lists the resources that make up the theme. Here is an
      example:<!--Is this an example of what a human enters? If not, why is it referred to as an example, if this is exact code already provided?--></para>

      <programlisting>styleSheet=/themes/cool/style.css
background=/themes/cool/img/coolBg.jpg</programlisting>

      <para>The keys of the properties are the names that refer to the themed
      elements from view code. For a JSP, you typically do this using the
      <literal>spring:theme</literal> custom tag, which is very similar to the
      <literal>spring:message</literal> tag. The following JSP fragment uses
      the theme defined in the previous example to customize the look and
      feel:</para>

      <programlisting language="xml">&lt;%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%&gt;
&lt;html&gt;
   &lt;head&gt;
      &lt;link rel="stylesheet" href="&lt;spring:theme code='styleSheet'/&gt;" type="text/css"/&gt;
   &lt;/head&gt;
   &lt;body style="background=&lt;spring:theme code='background'/&gt;"&gt;
      ...
   &lt;/body&gt;
&lt;/html&gt;</programlisting>

      <para>By default, the <classname>ResourceBundleThemeSource</classname>
      uses an empty base name prefix. As a result, the properties files are
      loaded from the root of the classpath. Thus you would put the
      <literal>cool.properties</literal> theme definition in a directory at
      the root of the classpath, for example, in
      <literal>/WEB-INF/classes</literal>. The
      <classname>ResourceBundleThemeSource</classname> uses the standard Java
      resource bundle loading mechanism, allowing for full
      internationalization of themes. For example, we could have a
      <literal>/WEB-INF/classes/cool_nl.properties</literal> that references a
      special background image with Dutch text on it.</para>
    </section>

    <section xml:id="mvc-themeresolver-resolving">
      <title>Theme resolvers</title>

      <para>After you define themes, as in the preceding section, you decide
      which theme to use. The <classname>DispatcherServlet</classname> will
      look for a bean named <classname>themeResolver</classname> to find out
      which <interfacename>ThemeResolver</interfacename> implementation to
      use. A theme resolver works in much the same way as a
      <interfacename>LocaleResolver</interfacename>. It detects the theme to
      use for a particular request and can also alter the request's theme. The
      following theme resolvers are provided by Spring:</para>

      <table xml:id="mvc-theme-resolver-impls-tbl">
        <title><interfacename>ThemeResolver</interfacename>
        implementations</title>

        <tgroup cols="2">
          <colspec colname="c1" colwidth="1*" />

          <colspec colname="c3" colwidth="3*" />

          <thead>
            <row>
              <entry>Class</entry>

              <entry>Description</entry>
            </row>
          </thead>

          <tbody>
            <row>
              <entry><classname>FixedThemeResolver</classname></entry>

              <entry>Selects a fixed theme, set using the
              <classname>defaultThemeName</classname> property.</entry>
            </row>

            <row>
              <entry><classname>SessionThemeResolver</classname></entry>

              <entry>The theme is maintained in the user's HTTP session. It
              only needs to be set once for each session, but is not persisted
              between sessions.</entry>
            </row>

            <row>
              <entry><classname>CookieThemeResolver</classname></entry>

              <entry>The selected theme is stored in a cookie on the
              client.</entry>
            </row>
          </tbody>
        </tgroup>
      </table>

      <para>Spring also provides a
      <classname>ThemeChangeInterceptor</classname> that allows theme changes
      on every request with a simple request parameter.<!--Do you need more info or an example re preceding sentence?--></para>
    </section>
  </section>

  <section xml:id="mvc-multipart">
    <title>Spring's multipart (file upload) support</title>

    <section xml:id="mvc-multipart-introduction">
      <title>Introduction</title>

      <para>Spring's built-in multipart support handles file uploads in web
      applications. You enable this multipart support with pluggable
      <interfacename>MultipartResolver</interfacename> objects, defined in the
      <literal>org.springframework.web.multipart</literal> package. Spring
      provides one <interfacename>MultipartResolver</interfacename>
      implementation for use with <link
      xl:href="http://jakarta.apache.org/commons/fileupload"> <emphasis>Commons
      FileUpload</emphasis></link> and another for use with Servlet 3.0
      multipart request parsing.</para>

      <para>By default, Spring does no multipart handling, because some
      developers want to handle multiparts themselves. You enable Spring
      multipart handling by adding a multipart resolver to the web
      application's context. Each request is inspected to see if it contains a
      multipart. If no multipart is found, the request continues as expected.
      If a multipart is found in the request, the
      <classname>MultipartResolver</classname> that has been declared in your
      context is used. After that, the multipart attribute in your request is
      treated like any other attribute.</para>
    </section>

    <section xml:id="mvc-multipart-resolver-commons">
      <title>Using a <interfacename>MultipartResolver</interfacename> with
      <emphasis>Commons FileUpload</emphasis></title>

      <para>The following example shows how to use the
      <classname>CommonsMultipartResolver</classname>:</para>

      <programlisting language="xml">&lt;bean id="multipartResolver"
    class="org.springframework.web.multipart.commons.CommonsMultipartResolver"&gt;

    <lineannotation>&lt;!-- one of the properties available; the maximum file size in bytes --&gt;</lineannotation>
    &lt;property name="maxUploadSize" value="100000"/&gt;
&lt;/bean&gt;</programlisting>

      <para>Of course you also need to put the appropriate jars in your
      classpath for the multipart resolver to work. In the case of the
      <classname>CommonsMultipartResolver</classname>, you need to use
      <literal>commons-fileupload.jar</literal>.</para>

      <para>When the Spring <classname>DispatcherServlet</classname> detects a
      multi-part request, it activates the resolver that has been declared in
      your context and hands over the request. The resolver then wraps the
      current <classname>HttpServletRequest</classname> into a
      <classname>MultipartHttpServletRequest</classname> that supports
      multipart file uploads. Using the
      <classname>MultipartHttpServletRequest</classname>, you can get
      information about the multiparts contained by this request and actually
      get access to the multipart files themselves in your controllers.</para>
    </section>

    <section xml:id="mvc-multipart-resolver-standard">
      <title>Using a <interfacename>MultipartResolver</interfacename> with
      <emphasis>Servlet 3.0</emphasis></title>

      <para>In order to use Servlet 3.0 based multipart parsing, you need to
      mark the <classname>DispatcherServlet</classname> with a
      <literal>"multipart-config"</literal> section in
      <filename>web.xml</filename>, or with a
      <classname>javax.servlet.MultipartConfigElement</classname> in
      programmatic Servlet registration, or in case of a custom Servlet class
      possibly with a
      <classname>javax.servlet.annotation.MultipartConfig</classname>
      annotation on your Servlet class. Configuration settings such as maximum
      sizes or storage locations need to be applied at that Servlet
      registration level as Servlet 3.0 does not allow for those settings to
      be done from the MultipartResolver.</para>

      <para>Once Servlet 3.0 multipart parsing has been enabled in one of the
      above mentioned ways you can add the
      <classname>StandardServletMultipartResolver</classname> to your Spring
      configuration:</para>

      <programlisting language="xml">&lt;bean id="multipartResolver"
    class="org.springframework.web.multipart.support.StandardServletMultipartResolver"&gt;
&lt;/bean&gt;</programlisting>
    </section>

    <section xml:id="mvc-multipart-forms">
      <title>Handling a file upload in a form</title>

      <para>After the <classname>MultipartResolver</classname> completes its
      job, the request is processed like any other. First, create a form with
      a file input that will allow the user to upload a form. The encoding
      attribute (<literal>enctype="multipart/form-data"</literal>) lets the
      browser know how to encode the form as multipart request:</para>

      <programlisting language="xml">&lt;html&gt;
    &lt;head&gt;
        &lt;title&gt;Upload a file please&lt;/title&gt;
    &lt;/head&gt;
    &lt;body&gt;
        &lt;h1&gt;Please upload a file&lt;/h1&gt;
        &lt;form method="post" action="/form" enctype="multipart/form-data"&gt;
            &lt;input type="text" name="name"/&gt;
            &lt;input type="file" name="file"/&gt;
            &lt;input type="submit"/&gt;
        &lt;/form&gt;
    &lt;/body&gt;
&lt;/html&gt;</programlisting>

      <para>The next step is to create a controller that handles the file
      upload. This controller is very similar to a <link
      linkend="mvc-ann-controller">normal annotated
      <interfacename>@Controller</interfacename></link>, except that we use
      <classname>MultipartHttpServletRequest</classname> or
      <filename>MultipartFile</filename> in the method parameters:</para>

      <programlisting language="java">@Controller
public class FileUploadController {

    @RequestMapping(value = "/form", method = RequestMethod.POST)
    public String handleFormUpload(@RequestParam("name") String name,
        @RequestParam("file") MultipartFile file) {

        if (!file.isEmpty()) {
            byte[] bytes = file.getBytes();
            <lineannotation>// store the bytes somewhere</lineannotation>
           return "redirect:uploadSuccess";
       } else {
           return "redirect:uploadFailure";
       }
    }

}</programlisting>

      <para>Note how the <interfacename>@RequestParam</interfacename> method
      parameters map to the input elements declared in the form. In this
      example, nothing is done with the <literal>byte[]</literal>, but in
      practice you can save it in a database, store it on the file system, and
      so on.</para>

      <para>When using Servlet 3.0 multipart parsing you can also use
      <classname>javax.servlet.http.Part</classname> for the method
      parameter:</para>

      <programlisting language="java">@Controller
public class FileUploadController {

    @RequestMapping(value = "/form", method = RequestMethod.POST)
    public String handleFormUpload(@RequestParam("name") String name,
        @RequestParam("file") Part file) {

        InputStream inputStream = file.getInputStream();
        <lineannotation>// store bytes from uploaded file somewhere</lineannotation>

        return "redirect:uploadSuccess";
    }

}</programlisting>
    </section>

    <section xml:id="mvc-multipart-forms-non-browsers">
      <title>Handling a file upload request from programmatic clients</title>

      <para>Multipart requests can also be submitted from non-browser clients
      in a RESTful service scenario. All of the above examples and
      configuration apply here as well. However, unlike browsers that
      typically submit files and simple form fields, a programmatic client can
      also send more complex data of a specific content type — for example a
      multipart request with a file and second part with JSON formatted data:
      <programlisting>POST /someUrl
Content-Type: multipart/mixed

--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="meta-data"
Content-Type: application/json; charset=UTF-8
Content-Transfer-Encoding: 8bit

{
  "name": "value"
}
--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="file-data"; filename="file.properties"
Content-Type: text/xml
Content-Transfer-Encoding: 8bit
... File Data ...</programlisting></para>

      <para>You could access the part named "meta-data" with a
      <interfacename>@RequestParam("meta-data") String
      metadata</interfacename> controller method argument. However, you would
      probably prefer to accept a strongly typed object initialized from the
      JSON formatted data in the body of the request part, very similar to the
      way <interfacename>@RequestBody</interfacename> converts the body of a
      non-multipart request to a target object with the help of an
      <classname>HttpMessageConverter</classname>.</para>

      <para>You can use the <interfacename>@RequestPart</interfacename>
      annotation instead of the <interfacename>@RequestParam</interfacename>
      annotation for this purpose. It allows you to have the content of a
      specific multipart passed through an
      <classname>HttpMessageConverter</classname> taking into consideration
      the <literal>'Content-Type'</literal> header of the multipart:</para>

      <programlisting language="java">@RequestMapping(value="/someUrl", method = RequestMethod.POST)
public String onSubmit(<emphasis role="bold">@RequestPart("meta-data") MetaData metadata,
                       @RequestPart("file-data") MultipartFile file</emphasis>) {
    <lineannotation>// ...</lineannotation>

}</programlisting>

      <para>Notice how <classname>MultipartFile</classname> method arguments
      can be accessed with <interfacename>@RequestParam</interfacename> or
      with <interfacename>@RequestPart</interfacename> interchangeably.
      However, the <literal>@RequestPart("meta-data") MetaData</literal>
      method argument in this case is read as JSON content based on its
      <literal>'Content-Type'</literal> header and converted with the help of
      the <classname>MappingJackson2HttpMessageConverter</classname>.</para>
    </section>
  </section>

  <section xml:id="mvc-exceptionhandlers">
    <title>Handling exceptions</title>

    <section xml:id="mvc-exceptionhandlers-resolver">
      <title
      xml:id="mvc-HandlerExceptionResolver"><interfacename>HandlerExceptionResolver</interfacename></title>

      <para>Spring <literal>HandlerExceptionResolver</literal> implementations
      deal with unexpected exceptions that occur during controller execution.
      A <literal>HandlerExceptionResolver</literal> somewhat resembles the
      exception mappings you can define in the web application descriptor
      <literal>web.xml</literal>. However, they provide a more flexible way to
      do so. For example they provide information about which handler was
      executing when the exception was thrown. Furthermore, a programmatic way
      of handling exceptions gives you more options for responding
      appropriately before the request is forwarded to another URL (the same
      end result as when you use the Servlet specific exception
      mappings).</para>

      <para>Besides implementing the
      <interfacename>HandlerExceptionResolver</interfacename> interface, which
      is only a matter of implementing the
      <literal>resolveException(Exception, Handler)</literal> method and
      returning a <classname>ModelAndView</classname>, you may also use the provided
      <classname>SimpleMappingExceptionResolver</classname> or create
      <interfacename>@ExceptionHandler</interfacename> methods.
      The <classname>SimpleMappingExceptionResolver</classname>
      enables you to take the class name of any exception that might be thrown
      and map it to a view name. This is functionally equivalent to the
      exception mapping feature from the Servlet API, but it is also possible
      to implement more finely grained mappings of exceptions from different
      handlers. The <interfacename>@ExceptionHandler</interfacename> annotation on
      the other hand can be used on methods that should be invoked to handle an
      exception. Such methods may be defined locally within an
      <interfacename>@Controller</interfacename> or may apply globally to all
      <interfacename>@RequestMapping</interfacename> methods when defined within
      an <interfacename>@ControllerAdvice</interfacename> class.
      The following sections explain this in more detail.</para>
    </section>

    <section xml:id="mvc-ann-exceptionhandler">
      <title><interfacename>@ExceptionHandler</interfacename></title>

      <para>The <interfacename>HandlerExceptionResolver</interfacename> interface
      and the <classname>SimpleMappingExceptionResolver</classname> implementations
      allow you to map Exceptions to specific views declaratively along with some
      optional Java logic before forwarding to those views. However, in some cases,
      especially when relying on <interfacename>@ResponseBody</interfacename> methods
      rather than on view resolution, it may be more convenient to directly set the
      status of the response and optionally write error content to the body of the
      response.</para>

      <para>You can do that with <interfacename>@ExceptionHandler</interfacename>
      methods. When declared within a controller such methods apply to exceptions
      raised by <interfacename>@RequestMapping</interfacename> methods of that
      contoroller (or any of its sub-classes). You can also declare an
      <interfacename>@ExceptionHandler</interfacename> method within an
      <interfacename>@ControllerAdvice</interfacename> class in which case it
      handles exceptions from <interfacename>@RequestMapping</interfacename>
      methods from any controller.
      The <interfacename>@ControllerAdvice</interfacename> annotation is
      a component annotation, which can be used with classpath scanning. It is
      automatically enabled when using the MVC namespace and the MVC Java config,
      or otherwise depending on whether the
      <classname>ExceptionHandlerExceptionResolver</classname> is configured or not.
      Below is an example of a controller-local
      <interfacename>@ExceptionHandler</interfacename> method:</para>

      <programlisting language="java">@Controller
public class SimpleController {


  // @RequestMapping methods omitted ...


  @ExceptionHandler(IOException.class)
  public ResponseEntity&lt;String&gt; handleIOException(IOException ex) {

    // prepare responseEntity

    return responseEntity;
  }

}</programlisting>

      <para>The <classname>@ExceptionHandler</classname> value can be set to
      an array of Exception types. If an exception is thrown that matches one of
      the types in the list, then the method annotated with the matching
      <classname>@ExceptionHandler</classname> will be invoked. If the
      annotation value is not set then the exception types listed as method
      arguments are used.</para>

      <para>Much like standard controller methods annotated with a
      <interfacename>@RequestMapping</interfacename> annotation, the method arguments
      and return values of <interfacename>@ExceptionHandler</interfacename> methods
      can be flexible. For example, the
      <classname>HttpServletRequest</classname> can be accessed in Servlet
      environments and the <classname>PortletRequest</classname> in Portlet
      environments. The return type can be a <classname>String</classname>,
      which is interpreted as a view name, a
      <classname>ModelAndView</classname> object, a
      <classname>ResponseEntity</classname>, or you can also add the
      <interfacename>@ResponseBody</interfacename> to have the method return value
      converted with message converters and written to the response stream.</para>

    </section>

    <section xml:id="mvc-ann-rest-spring-mvc-exceptions">
      <title>Handling Standard Spring MVC Exceptions</title>

      <para>Spring MVC may raise a number of exceptions while processing
      a request. The <classname>SimpleMappingExceptionResolver</classname> can easily
      map any exception to a default error view as needed.
      However, when working with clients that interpret responses in an automated
      way you will want to set specific status code on the response. Depending on
      the exception raised the status code may indicate a client error (4xx) or a
      server error (5xx).</para>

      <para>The <classname>DefaultHandlerExceptionResolver</classname> translates
      Spring MVC exceptions to specific error status codes. It is registered
      by default with the MVC namespace, the MVC Java config, and also by the
      the <classname>DispatcherServlet</classname> (i.e. when not using the MVC
      namespace or Java config). Listed below are some of the exceptions handled
      by this resolver and the corresponding status codes:
      <informaltable>
          <tgroup cols="2">
            <thead>
              <row>
                <entry>Exception</entry>

                <entry>HTTP Status Code</entry>
              </row>
            </thead>

            <tbody>
              <row>
                <entry><classname>BindException</classname></entry>

                <entry>400 (Bad Request)</entry>
              </row>

              <row>
                <entry><classname>ConversionNotSupportedException</classname></entry>

                <entry>500 (Internal Server Error)</entry>
              </row>

              <row>
                <entry><classname>HttpMediaTypeNotAcceptableException</classname></entry>

                <entry>406 (Not Acceptable)</entry>
              </row>

              <row>
                <entry><classname>HttpMediaTypeNotSupportedException</classname></entry>

                <entry>415 (Unsupported Media Type)</entry>
              </row>

              <row>
                <entry><classname>HttpMessageNotReadableException</classname></entry>

                <entry>400 (Bad Request)</entry>
              </row>

              <row>
                <entry><classname>HttpMessageNotWritableException</classname></entry>

                <entry>500 (Internal Server Error)</entry>
              </row>

              <row>
                <entry><classname>HttpRequestMethodNotSupportedException</classname></entry>

                <entry>405 (Method Not Allowed)</entry>
              </row>

              <row>
                <entry><classname>MethodArgumentNotValidException</classname></entry>

                <entry>400 (Bad Request)</entry>
              </row>

              <row>
                <entry><classname>MissingServletRequestParameterException</classname></entry>

                <entry>400 (Bad Request)</entry>
              </row>

              <row>
                <entry><classname>MissingServletRequestPartException</classname></entry>

                <entry>400 (Bad Request)</entry>
              </row>

              <row>
                <entry><classname>NoSuchRequestHandlingMethodException</classname></entry>

                <entry>404 (Not Found)</entry>
              </row>

              <row>
                <entry><classname>TypeMismatchException</classname></entry>

                <entry>400 (Bad Request)</entry>
              </row>
            </tbody>
          </tgroup>
        </informaltable>
        </para>

        <para>The <classname>DefaultHandlerExceptionResolver</classname> works
        transparently by setting the status of the response. However, it stops short
        of writing any error content to the body of the response while your
        application may need to add developer-friendly content to every error
        response for example when providing a REST API. You can prepare a
        <classname>ModelAndView</classname> and
        render error content through view resolution -- i.e. by configuring a
        <classname>ContentNeogitatingViewResolver</classname>,
        <classname>MappingJacksonJsonView</classname>, and so on. However, you
        may prefer to use <interfacename>@ExceptionHandler</interfacename>
        methods instead.</para>

        <para>If you prefer to write error content via
        <interfacename>@ExceptionHandler</interfacename> methods you can extend
        <classname>ResponseEntityExceptionHandler</classname> instead.
        This is a convenient base for <interfacename>@ControllerAdvice</interfacename>
        classes providing an <interfacename>@ExceptionHandler</interfacename>
        method to handle standard Spring MVC exceptions and return
        <classname>ResponseEntity</classname>. That allows you to customize the response
        and write error content with message converters. See the Javadoc of
        <classname>ResponseEntityExceptionHandler</classname> for more details.</para>
    </section>

    <section xml:id="mvc-ann-annotated-exceptions">
      <title>Annotating Business Exceptions With <interfacename>@ResponseStatus</interfacename></title>

      <para>A business exception can be annotated with
      <interfacename>@ResponseStatus</interfacename>. When the exception is raised,
      the <classname>ResponseStatusExceptionResolver</classname> handles it by
      setting the status of the response accordingly.
      By default the <classname>DispatcherServlet</classname> registers
      the <classname>ResponseStatusExceptionResolver</classname> and it is
      available for use.</para>

    </section>

    <section xml:id="mvc-ann-customer-servlet-container-error-page">
      <title>Customizing the Default Servlet Container Error Page</title>

        <para>When the status of the response is set to an error status code
        and the body of the response is empty, Servlet containers commonly render
        an HTML formatted error page.
        To customize the default error page of the container, you can
        declare an <code>&lt;error-page&gt;</code> element in
        <filename>web.xml</filename>. Up until Servlet 3, that element had to
        be mapped to a specific status code or exception type. Starting with
        Servlet 3 an error page does not need to be mapped, which effectively
        means the specified location customizes the default Servlet container
        error page.</para>

      <programlisting language="xml">&lt;error-page&gt;
    &lt;location&gt;/error&lt;/location&gt;
&lt;/error-page&gt;
</programlisting>

        <para>Note that the actual location for the error page can be a
        JSP page or some other URL within the container including one handled
        through an <interfacename>@Controller</interfacename> method:</para>

        <para>When writing error information, the status code and the error message
        set on the <interfacename>HttpServletResponse</interfacename> can be
        accessed through request attributes in a controller:</para>

<programlisting language="java">@Controller
public class ErrorController {

    @RequestMapping(value="/error", produces="application/json")
    @ResponseBody
    public Map&lt;String, Object&gt; handle(HttpServletRequest request) {

        Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
        map.put("status", request.getAttribute("javax.servlet.error.status_code"));
        map.put("reason", request.getAttribute("javax.servlet.error.message"));

        return map;
    }

}</programlisting>

        <para>or in a JSP:</para>

      <programlisting language="xml">&lt;%@ page contentType="application/json" pageEncoding="UTF-8"%&gt;
{
   status:&lt;%=request.getAttribute("javax.servlet.error.status_code") %&gt;,
   reason:&lt;%=request.getAttribute("javax.servlet.error.message") %&gt;
}</programlisting>

    </section>

  </section>

  <section xml:id="mvc-coc">
    <title>Convention over configuration support</title>

    <para>For a lot of projects, sticking to established conventions and
    having reasonable defaults is just what they (the projects) need, and
    Spring Web MVC now has explicit support for <emphasis>convention over
    configuration</emphasis>. What this means is that if you establish a set
    of naming conventions and suchlike, you can
    <emphasis>substantially</emphasis> cut down on the amount of configuration
    that is required to set up handler mappings, view resolvers,
    <classname>ModelAndView</classname> instances, etc. This is a great boon
    with regards to rapid prototyping, and can also lend a degree of (always
    good-to-have) consistency across a codebase should you choose to move
    forward with it into production.</para>

    <para>Convention-over-configuration support addresses the three core areas
    of MVC: models, views, and controllers.</para>

    <section xml:id="mvc-coc-ccnhm">
      <title>The Controller
      <classname>ControllerClassNameHandlerMapping</classname></title>

      <para>The <classname>ControllerClassNameHandlerMapping</classname> class
      is a <interfacename>HandlerMapping</interfacename> implementation that
      uses a convention to determine the mapping between request URLs and the
      <interfacename>Controller</interfacename> instances that are to handle
      those requests.</para>

      <para>Consider the following simple
      <interfacename>Controller</interfacename> implementation. Take special
      notice of the <emphasis>name</emphasis> of the class.<!--Re preceding sentence, I don't see where the name of the class is discussed in explanation following the example. See my next comment.--></para>

      <programlisting language="java">public class <emphasis role="bold">ViewShoppingCartController</emphasis> implements Controller {

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
        <lineannotation>// the implementation is not hugely important for this example...</lineannotation>
    }
}</programlisting>

      <para>Here is a snippet from the corresponding Spring Web MVC
      configuration file:</para>

      <programlisting language="xml">&lt;bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/&gt;

&lt;bean id="<emphasis role="bold">viewShoppingCart</emphasis>" class="x.y.z.ViewShoppingCartController"&gt;
    <lineannotation>&lt;!-- inject dependencies as required... --&gt;</lineannotation>
&lt;/bean&gt;</programlisting>

      <para>The <classname>ControllerClassNameHandlerMapping</classname> finds
      all of the various handler (or
      <interfacename>Controller</interfacename>) beans defined in its
      application context and strips <literal>Controller</literal> off the
      name to define its handler mappings. Thus,
      <classname>ViewShoppingCartController</classname> maps to the
      <literal>/viewshoppingcart*</literal> request URL.</para>

      <para>Let's look at some more examples so that the central idea becomes
      immediately familiar. (Notice all lowercase in the URLs, in contrast to
      camel-cased <interfacename>Controller</interfacename> class
      names.)</para>

      <itemizedlist>
        <listitem>
          <para><classname>WelcomeController</classname> maps to the
          <literal>/welcome*</literal> request URL</para>
        </listitem>

        <listitem>
          <para><classname>HomeController</classname> maps to the
          <literal>/home*</literal> request URL</para>
        </listitem>

        <listitem>
          <para><classname>IndexController</classname> maps to the
          <literal>/index*</literal> request URL</para>
        </listitem>

        <listitem>
          <para><classname>RegisterController</classname> maps to the
          <literal>/register*</literal> request URL</para>
        </listitem>
      </itemizedlist>

      <para>In the case of <classname>MultiActionController</classname>
      handler classes, the mappings generated are slightly more complex. The
      <interfacename>Controller</interfacename> names in the following
      examples are assumed to be <classname>MultiActionController</classname>
      implementations:</para>

      <itemizedlist>
        <listitem>
          <para><classname>AdminController</classname> maps to the
          <literal>/admin/*</literal> request URL</para>
        </listitem>

        <listitem>
          <para><classname>CatalogController</classname> maps to the
          <literal>/catalog/*</literal> request URL</para>
        </listitem>
      </itemizedlist>

      <para>If you follow the convention of naming your
      <interfacename>Controller</interfacename> implementations as
      <literal>xxx</literal><emphasis role="bold">Controller</emphasis>, the
      <classname>ControllerClassNameHandlerMapping</classname> saves you the
      tedium of defining and maintaining a potentially
      <emphasis>looooong</emphasis>
      <classname>SimpleUrlHandlerMapping</classname> (or suchlike).</para>

      <para>The <classname>ControllerClassNameHandlerMapping</classname> class
      extends the <classname>AbstractHandlerMapping</classname> base class so
      you can define <interfacename>HandlerInterceptor</interfacename>
      instances and everything else just as you would with many other
      <interfacename>HandlerMapping</interfacename> implementations.</para>
    </section>

    <section xml:id="mvc-coc-modelmap">
      <title>The Model <classname>ModelMap</classname>
      (<classname>ModelAndView</classname>)</title>

      <para>The <classname>ModelMap</classname> class is essentially a
      glorified <interfacename>Map</interfacename> that can make adding
      objects that are to be displayed in (or on) a
      <interfacename>View</interfacename> adhere to a common naming
      convention. Consider the following
      <interfacename>Controller</interfacename> implementation; notice that
      objects are added to the <classname>ModelAndView</classname> without any
      associated name specified.</para>

      <programlisting language="java">public class DisplayShoppingCartController implements Controller {

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {

        List cartItems = <lineannotation>// get a List of CartItem objects</lineannotation>
        User user = <lineannotation>// get the User doing the shopping</lineannotation>

        ModelAndView mav = new ModelAndView("displayShoppingCart"); <lineannotation>&lt;-- the logical view name</lineannotation>

        mav.addObject(cartItems); <lineannotation>&lt;-- look ma, no name, just the object</lineannotation>
        mav.addObject(user); <lineannotation>&lt;-- and again ma!</lineannotation>

        return mav;
    }
}</programlisting>

      <para>The <classname>ModelAndView</classname> class uses a
      <classname>ModelMap</classname> class that is a custom
      <interfacename>Map</interfacename> implementation that automatically
      generates a key for an object when an object is added to it. The
      strategy for determining the name for an added object is, in the case of
      a scalar object such as <classname>User</classname>, to use the short
      class name of the object's class. The following examples are names that
      are generated for scalar objects put into a
      <classname>ModelMap</classname> instance.</para>

      <itemizedlist>
        <listitem>
          <para>An <classname>x.y.User</classname> instance added will have
          the name <literal>user</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <classname>x.y.Registration</classname> instance added will
          have the name <literal>registration</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <classname>x.y.Foo</classname> instance added will have the
          name <literal>foo</literal> generated.</para>
        </listitem>

        <listitem>
          <para>A <classname>java.util.HashMap</classname> instance added will
          have the name <literal>hashMap</literal> generated. You probably
          want to be explicit about the name in this case because
          <literal>hashMap</literal> is less than intuitive.</para>
        </listitem>

        <listitem>
          <para>Adding <literal>null</literal> will result in an
          <classname>IllegalArgumentException</classname> being thrown. If the
          object (or objects) that you are adding could be
          <literal>null</literal>, then you will also want to be explicit
          about the name.</para>
        </listitem>
      </itemizedlist>

      <sidebar>
        <title>What, no automatic pluralization?</title>

        <para>Spring Web MVC's convention-over-configuration support does not
        support automatic pluralization. That is, you cannot add a
        <interfacename>List</interfacename> of <classname>Person</classname>
        objects to a <classname>ModelAndView</classname> and have the
        generated name be <classname>people</classname>.</para>

        <para>This decision was made after some debate, with the
        <quote>Principle of Least Surprise</quote> winning out in the
        end.</para>
      </sidebar>

      <para>The strategy for generating a name after adding a
      <interfacename>Set</interfacename> or a
      <interfacename>List</interfacename> is to peek into the collection, take
      the short class name of the first object in the collection, and use that
      with <literal>List</literal> appended to the name. The same applies to
      arrays although with arrays it is not necessary to peek into the array
      contents. A few examples will make the semantics of name generation for
      collections clearer:</para>

      <itemizedlist>
        <listitem>
          <para>An <classname>x.y.User[]</classname> array with zero or more
          <classname>x.y.User</classname> elements added will have the name
          <literal>userList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <classname>x.y.Foo[]</classname> array with zero or more
          <classname>x.y.User</classname> elements added will have the name
          <literal>fooList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>A <classname>java.util.ArrayList</classname> with one or more
          <classname>x.y.User</classname> elements added will have the name
          <literal>userList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>A <classname>java.util.HashSet</classname> with one or more
          <classname>x.y.Foo</classname> elements added will have the name
          <literal>fooList</literal> generated.</para>
        </listitem>

        <listitem>
          <para>An <emphasis role="bold">empty</emphasis>
          <classname>java.util.ArrayList</classname> will not be added at all
          (in effect, the <methodname>addObject(..)</methodname> call will
          essentially be a no-op).</para>
        </listitem>
      </itemizedlist>
    </section>

    <section xml:id="mvc-coc-r2vnt">
      <title>The View -
      <interfacename>RequestToViewNameTranslator</interfacename></title>

      <para>The <interfacename>RequestToViewNameTranslator</interfacename>
      interface determines a logical <interfacename>View</interfacename> name
      when no such logical view name is explicitly supplied. It has just one
      implementation, the
      <classname>DefaultRequestToViewNameTranslator</classname> class.</para>

      <para>The <classname>DefaultRequestToViewNameTranslator</classname> maps
      request URLs to logical view names, as with this example:</para>

      <programlisting language="java">public class RegistrationController implements Controller {

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
        <lineannotation>// process the request...</lineannotation>
        ModelAndView mav = new ModelAndView();
        <lineannotation>// add data as necessary to the model...</lineannotation>
        return mav;
        <lineannotation>// notice that no View or logical view name has been set</lineannotation>
    }
}</programlisting>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd"&gt;

    <lineannotation>&lt;!-- this bean with the well known name generates view names for us --&gt;</lineannotation>
    &lt;bean id="viewNameTranslator"
        class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/&gt;

    &lt;bean class="x.y.RegistrationController"&gt;
        <lineannotation>&lt;!-- inject dependencies as necessary --&gt;</lineannotation>
    &lt;/bean&gt;

    <lineannotation>&lt;!-- maps request URLs to Controller names --&gt;</lineannotation>
    &lt;bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/&gt;

    &lt;bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"&gt;
        &lt;property name="prefix" value="/WEB-INF/jsp/"/&gt;
        &lt;property name="suffix" value=".jsp"/&gt;
    &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>Notice how in the implementation of the
      <literal>handleRequest(..)</literal> method no
      <interfacename>View</interfacename> or logical view name is ever set on
      the <classname>ModelAndView</classname> that is returned. The
      <classname>DefaultRequestToViewNameTranslator</classname> is tasked with
      generating a <emphasis>logical view name</emphasis> from the URL of the
      request. In the case of the above
      <classname>RegistrationController</classname>, which is used in
      conjunction with the
      <classname>ControllerClassNameHandlerMapping</classname>, a request URL
      of <literal>http://localhost/registration.html</literal> results in a
      logical view name of <literal>registration</literal> being generated by
      the <classname>DefaultRequestToViewNameTranslator</classname>. This
      logical view name is then resolved into the
      <literal>/WEB-INF/jsp/registration.jsp</literal> view by the
      <classname>InternalResourceViewResolver</classname> bean.</para>

      <tip>
        <para>You do not need to define a
        <classname>DefaultRequestToViewNameTranslator</classname> bean
        explicitly. If you like the default settings of the
        <classname>DefaultRequestToViewNameTranslator</classname>, you can
        rely on the Spring Web MVC <classname>DispatcherServlet</classname> to
        instantiate an instance of this class if one is not explicitly
        configured.</para>
      </tip>

      <para>Of course, if you need to change the default settings, then you do
      need to configure your own
      <classname>DefaultRequestToViewNameTranslator</classname> bean
      explicitly. Consult the comprehensive Javadoc for the
      <classname>DefaultRequestToViewNameTranslator</classname> class for
      details of the various properties that can be configured.</para>
    </section>
  </section>

  <section xml:id="mvc-etag">
    <title>ETag support</title>

    <para>An <link xl:href="http://en.wikipedia.org/wiki/HTTP_ETag">ETag</link>
    (entity tag) is an HTTP response header returned by an HTTP/1.1 compliant
    web server used to determine change in content at a given URL. It can be
    considered to be the more sophisticated successor to the
    <literal>Last-Modified</literal> header. When a server returns a
    representation with an ETag header, the client can use this header in
    subsequent GETs, in an <literal>If-None-Match</literal> header. If the
    content has not changed, the server returns <literal>304: Not
    Modified</literal>.</para>

    <para>Support for ETags is provided by the Servlet filter
    <classname>ShallowEtagHeaderFilter</classname>. It is a plain Servlet
    Filter, and thus can be used in combination with any web framework. <!--The preceding sentence was a fragment, not a complete sentence. Have I reworded ok?-->The
    <classname>ShallowEtagHeaderFilter</classname> filter creates so-called
    shallow ETags (as opposed to deep ETags, more about that later).<!--Provide xref to deep ETags.-->The
    filter caches the content of the rendered JSP (or other content),
    generates an MD5 hash over that, and returns that as an ETag header in the
    response. The next time a client sends a request for the same resource, it
    uses that hash as the <literal>If-None-Match</literal> value. The filter
    detects this, renders the view again, and compares the two hashes. If they
    are equal, a <literal>304</literal> is returned. This filter will not save
    processing power, as the view is still rendered. The only thing it saves
    is bandwidth, as the rendered response is not sent back over the
    wire.</para>

    <para>You configure the <classname>ShallowEtagHeaderFilter</classname> in
    <filename>web.xml</filename>:</para>

    <programlisting language="xml">&lt;filter&gt;
  &lt;filter-name&gt;etagFilter&lt;/filter-name&gt;
    &lt;filter-class&gt;org.springframework.web.filter.ShallowEtagHeaderFilter&lt;/filter-class&gt;
&lt;/filter&gt;

&lt;filter-mapping&gt;
  &lt;filter-name&gt;etagFilter&lt;/filter-name&gt;
  &lt;servlet-name&gt;petclinic&lt;/servlet-name&gt;
&lt;/filter-mapping&gt;</programlisting>
  </section>

  <section xml:id="mvc-container-config">
    <title>Code-based Servlet container initialization</title>

    <para>In a Servlet 3.0+ environment, you  have the option of configuring the
    Servlet container programmatically as an alternative or in combination with
    a <filename>web.xml</filename> file.
    Below is an example of registering a <classname>DispatcherServlet</classname>:</para>

    <programlisting language="java">import org.springframework.web.WebApplicationInitializer;

public class MyWebApplicationInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext container) {
        XmlWebApplicationContext appContext = new XmlWebApplicationContext();
        appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");

        ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet(appContext));
        registration.setLoadOnStartup(1);
        registration.addMapping("/");
    }

}</programlisting>

    <para><interfacename>WebApplicationInitializer</interfacename> is an interface
    provided by Spring MVC that ensures your implementation is detected and
    automatically used to initialize any Servlet 3 container. An abstract base
    class implementation of <interfacename>WebApplicationInitializer</interfacename> named
    <classname>AbstractDispatcherServletInitializer</classname> makes it even
    easier to register the <classname>DispatcherServlet</classname> by simply overriding
    methods to specify the servlet mapping and the location of the
    <classname>DispatcherServlet</classname> configuration:</para>

    <programlisting language="java">public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class&lt;?&gt;[] getRootConfigClasses() {
        return null;
    }

    @Override
    protected Class&lt;?&gt;[] getServletConfigClasses() {
        return new Class[] { MyWebConfig.class };
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }

}</programlisting>

    <para>The above example is for an application that uses Java-based Spring
    configuration. If using XML-based Spring configuration, extend directly from
    <classname>AbstractDispatcherServletInitializer</classname>:</para>

    <programlisting language="java">public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {

    @Override
    protected WebApplicationContext createRootApplicationContext() {
        return null;
    }

    @Override
    protected WebApplicationContext createServletApplicationContext() {
        XmlWebApplicationContext cxt = new XmlWebApplicationContext();
        cxt.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");
        return cxt;
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }

}</programlisting>

    <para><classname>AbstractDispatcherServletInitializer</classname> also provides
    a convenient way to add <interfacename>Filter</interfacename> instances
    and have them automatically mapped to the <classname>DispatcherServlet</classname>:</para>

    <programlisting language="java">public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {

    // ...

    @Override
    protected Filter[] getServletFilters() {
        return new Filter[] { new HiddenHttpMethodFilter(), new CharacterEncodingFilter() };
    }

}</programlisting>

    <para>Each filter is added with a default name based on its concrete type and
    automatically mapped to the <classname>DispatcherServlet</classname>.</para>

    <para>The <code>isAsyncSupported</code> protected method of
    <classname>AbstractDispatcherServletInitializer</classname> provides
    a single place to enable async support on the <classname>DispatcherServlet</classname>
    and all filters mapped to it. By default this flag is set to <code>true</code>.</para>

  </section>

  <section xml:id="mvc-config">
    <title>Configuring Spring MVC</title>

    <para><xref linkend="mvc-servlet-special-bean-types"/> and
    <xref linkend="mvc-servlet-config"/> explained about
    Spring MVC's special beans and the default implementations
    used by the <classname>DispatcherServlet</classname>.
    In this section you'll learn about two additional ways of
    configuring Spring MVC. Namely the MVC Java config and
    the MVC XML namespace.
    </para>

    <para>The MVC Java config and the MVC namespace provide
    similar default configuration that overrides
    the <classname>DispatcherServlet</classname> defaults.
    The goal is to spare most applications from having to
    having to create the same configuration and also to
    provide higher-level constructs for configuring
    Spring MVC that serve as a simple starting point and
    require little or no prior knowledge of the underlying
    configuration.</para>

    <para>You can choose either the MVC Java config or the
    MVC namespace depending on your preference. Also as you
    will see further below, with the MVC Java config it is
    easier to see the underlying configuration as well as
    to make fine-grained customizations directly to the
    created Spring MVC beans.
    But let's start from the beginning.
    </para>

    <section xml:id="mvc-config-enable">
        <title>Enabling the MVC Java Config or the MVC XML Namespace</title>

        <para>To enable MVC Java config add the annotation
        <interfacename>@EnableWebMvc</interfacename> to one of your
        <interfacename>@Configuration</interfacename> classes:</para>

        <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig {

}</programlisting>

        <para>To achieve the same in XML use the <literal>mvc:annotation-driven</literal> element:</para>

        <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd"&gt;

    &lt;mvc:annotation-driven /&gt;

&lt;/beans&gt;</programlisting>

      <para>The above registers a
      <classname>RequestMappingHandlerMapping</classname>, a
      <classname>RequestMappingHandlerAdapter</classname>, and an
      <classname>ExceptionHandlerExceptionResolver</classname> (among others)
      in support of processing requests with annotated controller methods using
      annotations such as <interfacename>@RequestMapping </interfacename>,
      <interfacename>@ExceptionHandler</interfacename>, and others.</para>

      <para>It also enables the following:
      <orderedlist>
          <listitem>
            <para>Spring 3 style type conversion through a <link
            linkend="core-convert">ConversionService</link> instance
            in addition to the JavaBeans PropertyEditors used for Data Binding.</para>
          </listitem>

          <listitem>
            <para>Support for <link linkend="format">formatting</link> Number
            fields using the <interfacename>@NumberFormat</interfacename>
            annotation through the
            <interfacename>ConversionService</interfacename>.</para>
          </listitem>

          <listitem>
            <para>Support for <link linkend="format">formatting</link> Date,
            Calendar, Long, and Joda Time fields using the
            <interfacename>@DateTimeFormat</interfacename>
            annotation.</para>
          </listitem>

          <listitem>
            <para>Support for <link
            linkend="validation-mvc-jsr303">validating</link> @Controller
            inputs with <interfacename>@Valid</interfacename>,
            if a JSR-303 Provider is present on the classpath.</para>
          </listitem>

          <listitem>
            <para>HttpMessageConverter support for
            <interfacename>@RequestBody</interfacename> method
            parameters and <interfacename>@ResponseBody</interfacename>
            method return values from
            <interfacename>@RequestMapping</interfacename> or
            <interfacename>@ExceptionHandler</interfacename> methods.</para>

            <para>This is the complete list of HttpMessageConverters set up by
            mvc:annotation-driven: <itemizedlist>
                <listitem>
                  <para><classname>ByteArrayHttpMessageConverter</classname>
                  converts byte arrays.</para>
                </listitem>

                <listitem>
                  <para><classname>StringHttpMessageConverter</classname>
                  converts strings.</para>
                </listitem>

                <listitem>
                  <para><classname>ResourceHttpMessageConverter</classname>
                  converts to/from
                  <classname>org.springframework.core.io.Resource</classname>
                  for all media types.</para>
                </listitem>

                <listitem>
                  <para><classname>SourceHttpMessageConverter</classname>
                  converts to/from a
                  <classname>javax.xml.transform.Source</classname>.</para>
                </listitem>

                <listitem>
                  <para><classname>FormHttpMessageConverter</classname>
                  converts form data to/from a
                  <classname>MultiValueMap&lt;String,
                  String&gt;</classname>.</para>
                </listitem>

                <listitem>
                  <para><classname>Jaxb2RootElementHttpMessageConverter</classname>
                  converts Java objects to/from XML — added if JAXB2 is
                  present on the classpath.</para>
                </listitem>

                <listitem>
                  <para><classname>MappingJackson2HttpMessageConverter</classname>
                  (or <classname>MappingJacksonHttpMessageConverter</classname>)
                  converts to/from JSON — added if Jackson 2 (or Jackson) is present
                  on the classpath.</para>
                </listitem>

                <listitem>
                  <para><classname>AtomFeedHttpMessageConverter</classname>
                  converts Atom feeds — added if Rome is present on the
                  classpath.</para>
                </listitem>

                <listitem>
                  <para><classname>RssChannelHttpMessageConverter</classname>
                  converts RSS feeds — added if Rome is present on the
                  classpath.</para>
                </listitem>
              </itemizedlist></para>

          </listitem>
        </orderedlist>
        </para>
    </section>

    <section xml:id="mvc-config-customize">
        <title>Customizing the Provided Configuration</title>

        <para>To customize the default configuration in Java you simply
        implement the <interfacename>WebMvcConfigurer</interfacename>
        interface or more likely extend the class
        <classname>WebMvcConfigurerAdapter</classname> and override
        the methods you need. Below is an example of some of the available
        methods to override. See <interfacename>WebMvcConifgurer</interfacename> for
        a list of all methods and the Javadoc for further details:</para>

        <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  protected void addFormatters(FormatterRegistry registry) {
    // Add formatters and/or converters
  }

  @Override
  public void configureMessageConverters(List&lt;HttpMessageConverter&lt;?&gt;&gt; converters) {
    // Configure the list of HttpMessageConverters to use
  }

}</programlisting>

        <para>To customize the default configuration of
        <literal>&lt;mvc:annotation-driven /&gt;</literal> check what
        attributes and sub-elements it supports. You can view the
        <link xl:href="http://static.springsource.org/schema/mvc/spring-mvc.xsd">Spring MVC XML schema</link>
        or use the code completion feature of your IDE to discover
        what attributes and sub-elements are available.
        The sample below shows a subset of what is available:</para>

        <programlisting language="xml">&lt;mvc:annotation-driven conversion-service="conversionService"&gt;
    &lt;mvc:message-converters&gt;
        &lt;bean class="org.example.MyHttpMessageConverter"/&gt;
        &lt;bean class="org.example.MyOtherHttpMessageConverter"/&gt;
    &lt;/mvc:message-converters&gt;
&lt;/mvc:annotation-driven&gt;

&lt;bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean"&gt;
    &lt;property name="formatters"&gt;
        &lt;list&gt;
            &lt;bean class="org.example.MyFormatter"/&gt;
            &lt;bean class="org.example.MyOtherFormatter"/&gt;
        &lt;/list&gt;
    &lt;/property&gt;
&lt;/bean&gt;</programlisting>

    </section>

    <section xml:id="mvc-config-interceptors">
      <title>Configuring Interceptors</title>

      <para>You can configure <interfacename>HandlerInterceptors</interfacename>
      or <interfacename>WebRequestInterceptors</interfacename> to be applied
      to all incoming requests or restricted to specific URL path patterns.</para>

      <para>An example of registering interceptors in Java:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void addInterceptors(InterceptorRegistry registry) {
    registry.addInterceptor(new LocaleInterceptor());
    registry.addInterceptor(new ThemeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**");
    registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*");
 }

}</programlisting>

      <para>And in XML use the <literal>&lt;mvc:interceptors&gt;</literal> element:</para>

      <programlisting language="xml">&lt;mvc:interceptors&gt;
    &lt;bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor" /&gt;
    &lt;mvc:interceptor&gt;
        &lt;mapping path="/**"/&gt;
        &lt;exclude-mapping path="/admin/**"/&gt;
        &lt;bean class="org.springframework.web.servlet.theme.ThemeChangeInterceptor" /&gt;
    &lt;/mvc:interceptor&gt;
    &lt;mvc:interceptor&gt;
        &lt;mapping path="/secure/*"/&gt;
        &lt;bean class="org.example.SecurityInterceptor" /&gt;
    &lt;/mvc:interceptor&gt;
&lt;/mvc:interceptors&gt;
</programlisting>

    </section>

    <section xml:id="mvc-config-content-negotiation">
      <title>Configuring Content Negotiation</title>

      <para>Staring with Spring Framework 3.2, you can configure how Spring MVC
      determines the requested media types from the client for request mapping
      as well as for content negotiation purposes. The available options are
      to check the file extension in the request URI, the "Accept" header,
      a request parameter, as well as to fall back on a default content type.
      By default, file extension in the request URI is checked first and
      the "Accept" header is checked next.</para>

      <para>For file extensions in the request URI, the MVC Java config and
      the MVC namespace, automatically register extensions such as
      <filename>.json</filename>, <filename>.xml</filename>,
      <filename>.rss</filename>, and <filename>.atom</filename> if the
      corresponding dependencies such as Jackson, JAXB2, or Rome
      are present on the classpath. Additional extensions may be not need
      to be registered explicitly if they can be discovered via
      <classname>ServletContext.getMimeType(String)</classname> or the
      <emphasis>Java Activation Framework</emphasis>
      (see <classname>javax.activation.MimetypesFileTypeMap</classname>).</para>

      <para>Below is an example of customizing content negotiation
      options through the MVC Java config:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
    configurer.favorPathExtension(false).favorParameter(true);
  }
}</programlisting>

     <para>In the MVC namespace, the <code>&lt;mvc:annotation-driven&gt;</code> element
     has a <code>content-negotiation-manager</code> attribute, which expects a
     <classname>ContentNegotiationManager</classname> that in turn can be created
     with a <classname>ContentNegotiationManagerFactoryBean</classname>:</para>

     <programlisting language="xml">&lt;mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" /&gt;

&lt;bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean"&gt;
    &lt;property name="favorPathExtension" value="false" /&gt;
    &lt;property name="favorParameter" value="true" /&gt;
    &lt;property name="mediaTypes" &gt;
        &lt;value&gt;
            json=application/json
            xml=application/xml
        &lt;/value&gt;
    &lt;/property&gt;
&lt;/bean&gt;</programlisting>

      <para>If not using the MVC Java config or the MVC namespace, you'll need
      to create an instance of <classname>ContentNegotiationManager</classname>
      and use it to configure
      <classname>RequestMappingHandlerMapping</classname> for request mapping
      purposes, and <classname>RequestMappingHandlerAdapter</classname> and
      <classname>ExceptionHandlerExceptionResolver</classname> for
      content negotiation purposes.</para>

      <para>Note that <classname>ContentNegotiatingViewResolver</classname>
      now can also be configured with a <code>ContentNegotiatingViewResolver</code>,
      so you can use one instance throughout Spring MVC.</para>

      <para>In more advanced cases, it may be useful to configure
      multiple <classname>ContentNegotiationManager</classname> instances
      that in turn may contain custom
      <classname>ContentNegotiationStrategy</classname> implementations.
      For example you could configure
      <classname>ExceptionHandlerExceptionResolver</classname> with
      a <classname>ContentNegotiationManager</classname> that always
      resolves the requested media type to <filename>"application/json"</filename>.
      Or you may want to plug a custom strategy that has some logic to select
      a default content type (e.g. either XML or JSON) if no content
      types were requested.</para>

    </section>

    <section xml:id="mvc-config-view-controller">
      <title>Configuring View Controllers</title>

      <para>This is a shortcut for defining a
      <classname>ParameterizableViewController</classname> that immediately
      forwards to a view when invoked. Use it in static cases when there is no
      Java controller logic to execute before the view generates the
      response.</para>

      <para>An example of forwarding a request for <literal>"/"</literal>
      to a view called <literal>"home"</literal> in Java:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void addViewControllers(ViewControllerRegistry registry) {
    registry.addViewController("/").setViewName("home");
  }

}</programlisting>

      <para>And the same in XML use the <literal>&lt;mvc:view-controller&gt;</literal> element:</para>

      <programlisting language="xml">&lt;mvc:view-controller path="/" view-name="home"/&gt;</programlisting>
    </section>

    <section xml:id="mvc-config-static-resources">
      <title>Configuring Serving of Resources</title>

      <para>This option allows static resource requests following a particular
      URL pattern to be served by a
      <classname>ResourceHttpRequestHandler</classname> from any of a list of
      <classname>Resource</classname> locations. This provides a convenient
      way to serve static resources from locations other than the web
      application root, including locations on the classpath. The
      <code>cache-period</code> property may be used to set far future
      expiration headers (1 year is the recommendation of optimization tools
      such as Page Speed and YSlow) so that they will be more efficiently
      utilized by the client. The handler also properly evaluates the
      <code>Last-Modified</code> header (if present) so that a
      <code>304</code> status code will be returned as appropriate, avoiding
      unnecessary overhead for resources that are already cached by the
      client. For example, to serve resource requests with a URL pattern of
      <code>/resources/**</code> from a <code>public-resources</code>
      directory within the web application root you would use:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/");
  }

}</programlisting>

      <para>And the same in XML:</para>

      <programlisting language="xml">&lt;mvc:resources mapping="/resources/**" location="/public-resources/"/&gt;</programlisting>

      <para>To serve these resources with a 1-year future expiration to ensure
      maximum use of the browser cache and a reduction in HTTP requests made
      by the browser:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/").setCachePeriod(31556926);
  }

}</programlisting>

      <para>And in XML:</para>

      <programlisting language="xml">&lt;mvc:resources mapping="/resources/**" location="/public-resources/" cache-period="31556926"/&gt;</programlisting>

      <para>The <code>mapping</code> attribute must be an Ant pattern that can
      be used by <classname>SimpleUrlHandlerMapping</classname>, and the
      <code>location</code> attribute must specify one or more valid resource
      directory locations. Multiple resource locations may be specified using
      a comma-separated list of values. The locations specified will be
      checked in the specified order for the presence of the resource for any
      given request. For example, to enable the serving of resources from both
      the web application root and from a known path of
      <code>/META-INF/public-web-resources/</code> in any jar on the
      classpath use:</para>

      <programlisting language="java">@EnableWebMvc
@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/resources/**")
      .addResourceLocations("/", "classpath:/META-INF/public-web-resources/");
  }

}</programlisting>

      <para>And in XML:</para>

      <programlisting language="xml">&lt;mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/public-web-resources/"/&gt;</programlisting>

      <para>When serving resources that may change when a new version of the
      application is deployed, it is recommended that you incorporate a
      version string into the mapping pattern used to request the resources,
      so that you may force clients to request the newly deployed version of
      your application's resources. Such a version string can be parameterized
      and accessed using SpEL so that it may be easily managed in a single
      place when deploying new versions.</para>

      <para>As an example, let's consider an application that uses a
      performance-optimized custom build (as recommended) of the Dojo
      JavaScript library in production, and that the build is generally
      deployed within the web application at a path of
      <code>/public-resources/dojo/dojo.js</code>. Since different parts of
      Dojo may be incorporated into the custom build for each new version of
      the application, the client web browsers need to be forced to
      re-download that custom-built <code>dojo.js</code> resource any time a
      new version of the application is deployed. A simple way to achieve this
      would be to manage the version of the application in a properties file,
      such as:</para>

      <programlisting>application.version=1.0.0</programlisting>

      <para>and then to make the properties file's values accessible to SpEL
      as a bean using the <code>util:properties</code> tag:</para>

      <programlisting language="xml">&lt;util:properties id="applicationProps" location="/WEB-INF/spring/application.properties"/&gt;</programlisting>

      <para>With the application version now accessible via SpEL, we can
      incorporate this into the use of the <code>resources</code> tag:</para>

      <programlisting language="xml">&lt;mvc:resources mapping="/resources-#{applicationProps['application.version']}/**" location="/public-resources/"/&gt;</programlisting>

      <para>In Java, you can use the <interfacename>@PropertySouce</interfacename>
      annotation and then inject the <classname>Environment</classname>
      abstraction for access to all defined properties:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
@PropertySource("/WEB-INF/spring/application.properties")
public class WebConfig extends WebMvcConfigurerAdapter {

  @Inject Environment env;

  @Override
  public void addResourceHandlers(ResourceHandlerRegistry registry) {
    registry.addResourceHandler("/resources-" + env.getProperty("application.version") + "/**")
      .addResourceLocations("/public-resources/");
  }

}</programlisting>

      <para>and finally, to request the resource with the proper URL, we can
      take advantage of the Spring JSP tags:</para>

      <programlisting language="xml">&lt;spring:eval expression="@applicationProps['application.version']" var="applicationVersion"/&gt;

&lt;spring:url value="/resources-{applicationVersion}" var="resourceUrl"&gt;
    &lt;spring:param name="applicationVersion" value="${applicationVersion}"/&gt;
&lt;/spring:url&gt;

&lt;script src="${resourceUrl}/dojo/dojo.js" type="text/javascript"&gt; &lt;/script&gt;</programlisting>
    </section>

    <section xml:id="mvc-default-servlet-handler">
      <title>mvc:default-servlet-handler</title>

      <para>This tag allows for mapping the <code>DispatcherServlet</code> to
      "/" (thus overriding the mapping of the container's default Servlet),
      while still allowing static resource requests to be handled by the
      container's default Servlet. It configures a
      <code>DefaultServletHttpRequestHandler</code> with a URL mapping of
      "/**" and the lowest priority relative to other URL mappings.</para>

      <para>This handler will forward all requests to the default Servlet.
      Therefore it is important that it remains last in the order of all other
      URL <code>HandlerMappings</code>. That will be the case if you use
      <code>&lt;mvc:annotation-driven&gt;</code> or alternatively if you are
      setting up your own customized <code>HandlerMapping</code> instance be
      sure to set its <code>order</code> property to a value lower than that
      of the <code>DefaultServletHttpRequestHandler</code>, which is
      <code>Integer.MAX_VALUE</code>.</para>

      <para>To enable the feature using the default setup use:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
    configurer.enable();
  }

}</programlisting>

      <para>Or in XML:</para>

      <programlisting language="xml">&lt;mvc:default-servlet-handler/&gt;</programlisting>

      <para>The caveat to overriding the "/" Servlet mapping is that the
      <code>RequestDispatcher</code> for the default Servlet must be retrieved
      by name rather than by path. The
      <code>DefaultServletHttpRequestHandler</code> will attempt to
      auto-detect the default Servlet for the container at startup time, using
      a list of known names for most of the major Servlet containers
      (including Tomcat, Jetty, GlassFish, JBoss, Resin, WebLogic, and
      WebSphere). If the default Servlet has been custom configured with a
      different name, or if a different Servlet container is being used where
      the default Servlet name is unknown, then the default Servlet's name
      must be explicitly provided as in the following example:</para>

      <programlisting language="java">@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {

  @Override
  public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
    configurer.enable("myCustomDefaultServlet");
  }

}</programlisting>

      <para>Or in XML:</para>

      <programlisting language="xml">&lt;mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/&gt;</programlisting>
    </section>

    <section xml:id="mvc-resources">
      <title>More Spring Web MVC Resources</title>

      <para>See the following links and pointers for more resources about Spring Web MVC:</para>

      <itemizedlist>
        <listitem>
          <para>There are many excellent articles and tutorials that show how to
          build web applications with Spring MVC. Read them at the <link
          xl:href="http://www.springsource.org/documentation">Spring
          Documentation</link> page.</para>
        </listitem>

        <listitem>
          <para><quote>Expert Spring Web MVC and Web Flow</quote> by Seth Ladd
          and others (published by Apress) is an excellent hard copy source of
          Spring Web MVC goodness.</para>
        </listitem>
      </itemizedlist>
    </section>

    <section xml:id="mvc-config-advanced-java">
      <title>Advanced Customizations with MVC Java Config</title>

      <para>As you can see from the above examples, MVC Java config and
      the MVC namespace provide higher level constructs that do not
      require deep knowledge of the underlying beans created for you.
      Instead it helps you to focus on your application needs.
      However, at some point you may need more fine-grained control
      or you may simply wish to understand the underlying configuration.</para>

      <para>The first step towards more fine-grained control is to see the
      underlying beans created for you. In MVC Java config you can
      see the Javadoc and the <interfacename>@Bean</interfacename>
      methods in <classname>WebMvcConfigurationSupport</classname>.
      The configuration in this class is automatically imported
      through the <interfacename>@EnableWebMvc</interfacename> annotation.
      In fact if you open <interfacename>@EnableWebMvc</interfacename> you can
      see the <interfacename>@Import</interfacename> statement.</para>

      <para>The next step towards more fine-grained control is to
      customize a property on one of the beans created in
      <classname>WebMvcConfigurationSupport</classname> or perhaps
      to provide your own instance. This requires two things --
      remove the <interfacename>@EnableWebMvc</interfacename>
      annotation in order to prevent the import and then
      extend directly from <classname>WebMvcConfigurationSupport</classname>.
      Here is an example:
      </para>

      <programlisting language="java">@Configuration
public class WebConfig extends WebMvcConfigurationSupport {

  @Override
  public void addInterceptors(InterceptorRegistry registry){
    // ...
  }

  @Override
  @Bean
  public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {

      // Create or let "super" create the adapter
      // Then customize one of its properties
  }

}</programlisting>

      <para>Note that modifying beans in this way does not prevent
      you from using any of the higher-level constructs shown earlier in
      this section. </para>

    </section>

    <section xml:id="mvc-config-advanced-xml">
      <title>Advanced Customizations with the MVC Namespace</title>

      <para>Fine-grained control over the configuration created for
      you is a bit harder with the MVC namespace.</para>

      <para>If you do need to do that, rather than replicating the
      configuration it provides, consider configuring a
      <interfacename>BeanPostProcessor</interfacename> that detects
      the bean you want to customize by type and then modifying its
      properties as necessary. For example:</para>

    <programlisting language="java">@Component
public class MyPostProcessor implements BeanPostProcessor {

  public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException {
    if (bean instanceof RequestMappingHandlerAdapter) {
      // Modify properties of the adapter
    }
  }

}</programlisting>

      <para>Note that <classname>MyPostProcessor</classname> needs to be
      included in an <interfacename>&lt;component scan /&gt;</interfacename>
      in order for it to be detected or if you prefer you can declare it
      explicitly with an XML bean declaration.</para>
    </section>

  </section>

</chapter>
