/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.aop.framework;

import java.io.Serializable;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.UndeclaredThrowableException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.WeakHashMap;

import org.springframework.cglib.core.CodeGenerationException;
import org.springframework.cglib.proxy.Callback;
import org.springframework.cglib.proxy.CallbackFilter;
import org.springframework.cglib.proxy.Dispatcher;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.Factory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
import org.springframework.cglib.proxy.NoOp;
import org.springframework.cglib.transform.impl.UndeclaredThrowableStrategy;

import org.aopalliance.aop.Advice;
import org.aopalliance.intercept.MethodInvocation;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.aop.Advisor;
import org.springframework.aop.AopInvocationException;
import org.springframework.aop.PointcutAdvisor;
import org.springframework.aop.RawTargetAccess;
import org.springframework.aop.TargetSource;
import org.springframework.aop.support.AopUtils;
import org.springframework.core.SmartClassLoader;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;

/**
 * CGLIB-based {@link AopProxy} implementation for the Spring AOP framework.
 *
 * <p>Formerly named {@code Cglib2AopProxy}, as of Spring 3.2, this class depends on
 * Spring's own internally repackaged version of CGLIB 3.</i>.
 *
 * <p>Objects of this type should be obtained through proxy factories,
 * configured by an {@link AdvisedSupport} object. This class is internal
 * to Spring's AOP framework and need not be used directly by client code.
 *
 * <p>{@link DefaultAopProxyFactory} will automatically create CGLIB-based
 * proxies if necessary, for example in case of proxying a target class
 * (see the {@link DefaultAopProxyFactory attendant javadoc} for details).
 *
 * <p>Proxies created using this class are thread-safe if the underlying
 * (target) class is thread-safe.
 *
 * @author Rod Johnson
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @author Ramnivas Laddad
 * @author Chris Beams
 * @author Dave Syer
 * @see org.springframework.cglib.proxy.Enhancer
 * @see AdvisedSupport#setProxyTargetClass
 * @see DefaultAopProxyFactory
 */
@SuppressWarnings("serial")
final class CglibAopProxy implements AopProxy, Serializable {

	// Constants for CGLIB callback array indices
	private static final int AOP_PROXY = 0;
	private static final int INVOKE_TARGET = 1;
	private static final int NO_OVERRIDE = 2;
	private static final int DISPATCH_TARGET = 3;
	private static final int DISPATCH_ADVISED = 4;
	private static final int INVOKE_EQUALS = 5;
	private static final int INVOKE_HASHCODE = 6;


	/** Logger available to subclasses; static to optimize serialization */
	protected final static Log logger = LogFactory.getLog(CglibAopProxy.class);

	/** Keeps track of the Classes that we have validated for final methods */
	private static final Map<Class<?>, Boolean> validatedClasses = new WeakHashMap<Class<?>, Boolean>();


	/** The configuration used to configure this proxy */
	protected final AdvisedSupport advised;

	private Object[] constructorArgs;

	private Class<?>[] constructorArgTypes;

	/** Dispatcher used for methods on Advised */
	private final transient AdvisedDispatcher advisedDispatcher;

	private transient Map<String, Integer> fixedInterceptorMap;

	private transient int fixedInterceptorOffset;


	/**
	 * Create a new CglibAopProxy for the given AOP configuration.
	 * @param config the AOP configuration as AdvisedSupport object
	 * @throws AopConfigException if the config is invalid. We try to throw an informative
	 * exception in this case, rather than let a mysterious failure happen later.
	 */
	public CglibAopProxy(AdvisedSupport config) throws AopConfigException {
		Assert.notNull(config, "AdvisedSupport must not be null");
		if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
			throw new AopConfigException("No advisors and no TargetSource specified");
		}
		this.advised = config;
		this.advisedDispatcher = new AdvisedDispatcher(this.advised);
	}

	/**
	 * Set constructor arguments to use for creating the proxy.
	 * @param constructorArgs the constructor argument values
	 * @param constructorArgTypes the constructor argument types
	 */
	public void setConstructorArguments(Object[] constructorArgs, Class<?>[] constructorArgTypes) {
		if (constructorArgs == null || constructorArgTypes == null) {
			throw new IllegalArgumentException("Both 'constructorArgs' and 'constructorArgTypes' need to be specified");
		}
		if (constructorArgs.length != constructorArgTypes.length) {
			throw new IllegalArgumentException("Number of 'constructorArgs' (" + constructorArgs.length +
					") must match number of 'constructorArgTypes' (" + constructorArgTypes.length + ")");
		}
		this.constructorArgs = constructorArgs;
		this.constructorArgTypes = constructorArgTypes;
	}


	public Object getProxy() {
		return getProxy(null);
	}

	public Object getProxy(ClassLoader classLoader) {
		if (logger.isDebugEnabled()) {
			logger.debug("Creating CGLIB proxy: target source is " + this.advised.getTargetSource());
		}

		try {
			Class<?> rootClass = this.advised.getTargetClass();
			Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");

			Class<?> proxySuperClass = rootClass;
			if (ClassUtils.isCglibProxyClass(rootClass)) {
				proxySuperClass = rootClass.getSuperclass();
				Class<?>[] additionalInterfaces = rootClass.getInterfaces();
				for (Class<?> additionalInterface : additionalInterfaces) {
					this.advised.addInterface(additionalInterface);
				}
			}

			// Validate the class, writing log messages as necessary.
			validateClassIfNecessary(proxySuperClass);

			// Configure CGLIB Enhancer...
			Enhancer enhancer = createEnhancer();
			if (classLoader != null) {
				enhancer.setClassLoader(classLoader);
				if (classLoader instanceof SmartClassLoader &&
						((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
					enhancer.setUseCache(false);
				}
			}
			enhancer.setSuperclass(proxySuperClass);
			enhancer.setStrategy(new UndeclaredThrowableStrategy(UndeclaredThrowableException.class));
			enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
			enhancer.setInterceptDuringConstruction(false);

			Callback[] callbacks = getCallbacks(rootClass);
			enhancer.setCallbacks(callbacks);
			enhancer.setCallbackFilter(new ProxyCallbackFilter(
					this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));

			Class<?>[] types = new Class[callbacks.length];
			for (int x = 0; x < types.length; x++) {
				types[x] = callbacks[x].getClass();
			}
			enhancer.setCallbackTypes(types);

			// Generate the proxy class and create a proxy instance.
			Object proxy;
			if (this.constructorArgs != null) {
				proxy = enhancer.create(this.constructorArgTypes, this.constructorArgs);
			}
			else {
				proxy = enhancer.create();
			}

			return proxy;
		}
		catch (CodeGenerationException ex) {
			throw new AopConfigException("Could not generate CGLIB subclass of class [" +
					this.advised.getTargetClass() + "]: " +
					"Common causes of this problem include using a final class or a non-visible class",
					ex);
		}
		catch (IllegalArgumentException ex) {
			throw new AopConfigException("Could not generate CGLIB subclass of class [" +
					this.advised.getTargetClass() + "]: " +
					"Common causes of this problem include using a final class or a non-visible class",
					ex);
		}
		catch (Exception ex) {
			// TargetSource.getTarget() failed
			throw new AopConfigException("Unexpected AOP exception", ex);
		}
	}

	/**
	 * Creates the CGLIB {@link Enhancer}. Subclasses may wish to override this to return a custom
	 * {@link Enhancer} implementation.
	 */
	protected Enhancer createEnhancer() {
		return new Enhancer();
	}

	/**
	 * Checks to see whether the supplied {@code Class} has already been validated and
	 * validates it if not.
	 */
	private void validateClassIfNecessary(Class<?> proxySuperClass) {
		if (logger.isWarnEnabled()) {
			synchronized (validatedClasses) {
				if (!validatedClasses.containsKey(proxySuperClass)) {
					doValidateClass(proxySuperClass);
					validatedClasses.put(proxySuperClass, Boolean.TRUE);
				}
			}
		}
	}

	/**
	 * Checks for final methods on the {@code Class} and writes warnings to the log
	 * for each one found.
	 */
	private void doValidateClass(Class<?> proxySuperClass) {
		Method[] methods = proxySuperClass.getMethods();
		for (Method method : methods) {
			if (!Object.class.equals(method.getDeclaringClass()) && Modifier.isFinal(method.getModifiers())) {
				logger.warn("Unable to proxy method [" + method + "] because it is final: " +
						"All calls to this method via a proxy will be routed directly to the proxy.");
			}
		}
	}

	private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
		// Parameters used for optimisation choices...
		boolean exposeProxy = this.advised.isExposeProxy();
		boolean isFrozen = this.advised.isFrozen();
		boolean isStatic = this.advised.getTargetSource().isStatic();

		// Choose an "aop" interceptor (used for AOP calls).
		Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);

		// Choose a "straight to target" interceptor. (used for calls that are
		// unadvised but can return this). May be required to expose the proxy.
		Callback targetInterceptor;
		if (exposeProxy) {
			targetInterceptor = isStatic ?
					new StaticUnadvisedExposedInterceptor(this.advised.getTargetSource().getTarget()) :
					new DynamicUnadvisedExposedInterceptor(this.advised.getTargetSource());
		}
		else {
			targetInterceptor = isStatic ?
					new StaticUnadvisedInterceptor(this.advised.getTargetSource().getTarget()) :
					new DynamicUnadvisedInterceptor(this.advised.getTargetSource());
		}

		// Choose a "direct to target" dispatcher (used for
		// unadvised calls to static targets that cannot return this).
		Callback targetDispatcher = isStatic ?
				new StaticDispatcher(this.advised.getTargetSource().getTarget()) : new SerializableNoOp();

		Callback[] mainCallbacks = new Callback[]{
			aopInterceptor, // for normal advice
			targetInterceptor, // invoke target without considering advice, if optimized
			new SerializableNoOp(), // no override for methods mapped to this
			targetDispatcher, this.advisedDispatcher,
			new EqualsInterceptor(this.advised),
			new HashCodeInterceptor(this.advised)
		};

		Callback[] callbacks;

		// If the target is a static one and the advice chain is frozen,
		// then we can make some optimisations by sending the AOP calls
		// direct to the target using the fixed chain for that method.
		if (isStatic && isFrozen) {
			Method[] methods = rootClass.getMethods();
			Callback[] fixedCallbacks = new Callback[methods.length];
			this.fixedInterceptorMap = new HashMap<String, Integer>(methods.length);

			// TODO: small memory optimisation here (can skip creation for
			// methods with no advice)
			for (int x = 0; x < methods.length; x++) {
				List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(methods[x], rootClass);
				fixedCallbacks[x] = new FixedChainStaticTargetInterceptor(
						chain, this.advised.getTargetSource().getTarget(), this.advised.getTargetClass());
				this.fixedInterceptorMap.put(methods[x].toString(), x);
			}

			// Now copy both the callbacks from mainCallbacks
			// and fixedCallbacks into the callbacks array.
			callbacks = new Callback[mainCallbacks.length + fixedCallbacks.length];
			System.arraycopy(mainCallbacks, 0, callbacks, 0, mainCallbacks.length);
			System.arraycopy(fixedCallbacks, 0, callbacks, mainCallbacks.length, fixedCallbacks.length);
			this.fixedInterceptorOffset = mainCallbacks.length;
		}
		else {
			callbacks = mainCallbacks;
		}
		return callbacks;
	}

	/**
	 * Process a return value. Wraps a return of {@code this} if necessary to be the
	 * {@code proxy} and also verifies that {@code null} is not returned as a primitive.
	 */
	private static Object processReturnType(Object proxy, Object target, Method method, Object retVal) {
		// Massage return value if necessary
		if (retVal != null && retVal == target &&
				!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
			// Special case: it returned "this".
			// Note that we can't help if the target sets a reference
			// to itself in another returned object.
			retVal = proxy;
		}
		Class<?> returnType = method.getReturnType();
		if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
				throw new AopInvocationException("Null return value from advice does not match primitive return type for: " + method);
		}
		return retVal;
	}


	@Override
	public boolean equals(Object other) {
		return (this == other || (other instanceof CglibAopProxy &&
				AopProxyUtils.equalsInProxy(this.advised, ((CglibAopProxy) other).advised)));
	}

	@Override
	public int hashCode() {
		return CglibAopProxy.class.hashCode() * 13 + this.advised.getTargetSource().hashCode();
	}


	/**
	 * Serializable replacement for CGLIB's NoOp interface.
	 * Public to allow use elsewhere in the framework.
	 */
	public static class SerializableNoOp implements NoOp, Serializable {
	}


	/**
	 * Method interceptor used for static targets with no advice chain. The call
	 * is passed directly back to the target. Used when the proxy needs to be
	 * exposed and it can't be determined that the method won't return
	 * {@code this}.
	 */
	private static class StaticUnadvisedInterceptor implements MethodInterceptor, Serializable {

		private final Object target;

		public StaticUnadvisedInterceptor(Object target) {
			this.target = target;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
			Object retVal = methodProxy.invoke(this.target, args);
			return processReturnType(proxy, this.target, method, retVal);
		}
	}


	/**
	 * Method interceptor used for static targets with no advice chain, when the
	 * proxy is to be exposed.
	 */
	private static class StaticUnadvisedExposedInterceptor implements MethodInterceptor, Serializable {

		private final Object target;

		public StaticUnadvisedExposedInterceptor(Object target) {
			this.target = target;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
			Object oldProxy = null;
			try {
				oldProxy = AopContext.setCurrentProxy(proxy);
				Object retVal = methodProxy.invoke(this.target, args);
				return processReturnType(proxy, this.target, method, retVal);
			}
			finally {
				AopContext.setCurrentProxy(oldProxy);
			}
		}
	}


	/**
	 * Interceptor used to invoke a dynamic target without creating a method
	 * invocation or evaluating an advice chain. (We know there was no advice
	 * for this method.)
	 */
	private static class DynamicUnadvisedInterceptor implements MethodInterceptor, Serializable {

		private final TargetSource targetSource;

		public DynamicUnadvisedInterceptor(TargetSource targetSource) {
			this.targetSource = targetSource;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
			Object target = this.targetSource.getTarget();
			try {
				Object retVal = methodProxy.invoke(target, args);
				return processReturnType(proxy, target, method, retVal);
			}
			finally {
				this.targetSource.releaseTarget(target);
			}
		}
	}


	/**
	 * Interceptor for unadvised dynamic targets when the proxy needs exposing.
	 */
	private static class DynamicUnadvisedExposedInterceptor implements MethodInterceptor, Serializable {

		private final TargetSource targetSource;

		public DynamicUnadvisedExposedInterceptor(TargetSource targetSource) {
			this.targetSource = targetSource;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
			Object oldProxy = null;
			Object target = this.targetSource.getTarget();
			try {
				oldProxy = AopContext.setCurrentProxy(proxy);
				Object retVal = methodProxy.invoke(target, args);
				return processReturnType(proxy, target, method, retVal);
			}
			finally {
				AopContext.setCurrentProxy(oldProxy);
				this.targetSource.releaseTarget(target);
			}
		}
	}


	/**
	 * Dispatcher for a static target. Dispatcher is much faster than
	 * interceptor. This will be used whenever it can be determined that a
	 * method definitely does not return "this"
	 */
	private static class StaticDispatcher implements Dispatcher, Serializable {

		private Object target;

		public StaticDispatcher(Object target) {
			this.target = target;
		}

		public Object loadObject() {
			return this.target;
		}
	}


	/**
	 * Dispatcher for any methods declared on the Advised class.
	 */
	private static class AdvisedDispatcher implements Dispatcher, Serializable {

		private final AdvisedSupport advised;

		public AdvisedDispatcher(AdvisedSupport advised) {
			this.advised = advised;
		}

		public Object loadObject() throws Exception {
			return this.advised;
		}
	}


	/**
	 * Dispatcher for the {@code equals} method.
	 * Ensures that the method call is always handled by this class.
	 */
	private static class EqualsInterceptor implements MethodInterceptor, Serializable {

		private final AdvisedSupport advised;

		public EqualsInterceptor(AdvisedSupport advised) {
			this.advised = advised;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) {
			Object other = args[0];
			if (proxy == other) {
				return true;
			}
			if (other instanceof Factory) {
				Callback callback = ((Factory) other).getCallback(INVOKE_EQUALS);
				if (!(callback instanceof EqualsInterceptor)) {
					return false;
				}
				AdvisedSupport otherAdvised = ((EqualsInterceptor) callback).advised;
				return AopProxyUtils.equalsInProxy(this.advised, otherAdvised);
			}
			else {
				return false;
			}
		}
	}


	/**
	 * Dispatcher for the {@code hashCode} method.
	 * Ensures that the method call is always handled by this class.
	 */
	private static class HashCodeInterceptor implements MethodInterceptor, Serializable {

		private final AdvisedSupport advised;

		public HashCodeInterceptor(AdvisedSupport advised) {
			this.advised = advised;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) {
			return CglibAopProxy.class.hashCode() * 13 + this.advised.getTargetSource().hashCode();
		}
	}


	/**
	 * Interceptor used specifically for advised methods on a frozen, static proxy.
	 */
	private static class FixedChainStaticTargetInterceptor implements MethodInterceptor, Serializable {

		private final List<Object> adviceChain;

		private final Object target;

		private final Class<?> targetClass;

		public FixedChainStaticTargetInterceptor(List<Object> adviceChain, Object target, Class<?> targetClass) {
			this.adviceChain = adviceChain;
			this.target = target;
			this.targetClass = targetClass;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
			MethodInvocation invocation = new CglibMethodInvocation(proxy, this.target, method, args,
					this.targetClass, this.adviceChain, methodProxy);
			// If we get here, we need to create a MethodInvocation.
			Object retVal = invocation.proceed();
			retVal = processReturnType(proxy, this.target, method, retVal);
			return retVal;
		}
	}


	/**
	 * General purpose AOP callback. Used when the target is dynamic or when the
	 * proxy is not frozen.
	 */
	private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {

		private AdvisedSupport advised;

		public DynamicAdvisedInterceptor(AdvisedSupport advised) {
			this.advised = advised;
		}

		public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
			Object oldProxy = null;
			boolean setProxyContext = false;
			Class<?> targetClass = null;
			Object target = null;
			try {
				if (this.advised.exposeProxy) {
					// Make invocation available if necessary.
					oldProxy = AopContext.setCurrentProxy(proxy);
					setProxyContext = true;
				}
				// May be null Get as late as possible to minimize the time we
				// "own" the target, in case it comes from a pool.
				target = getTarget();
				if (target != null) {
					targetClass = target.getClass();
				}
				List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
				Object retVal;
				// Check whether we only have one InvokerInterceptor: that is,
				// no real advice, but just reflective invocation of the target.
				if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
					// We can skip creating a MethodInvocation: just invoke the target directly.
					// Note that the final invoker must be an InvokerInterceptor, so we know
					// it does nothing but a reflective operation on the target, and no hot
					// swapping or fancy proxying.
					retVal = methodProxy.invoke(target, args);
				}
				else {
					// We need to create a method invocation...
					retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
				}
				retVal = processReturnType(proxy, target, method, retVal);
				return retVal;
			}
			finally {
				if (target != null) {
					releaseTarget(target);
				}
				if (setProxyContext) {
					// Restore old proxy.
					AopContext.setCurrentProxy(oldProxy);
				}
			}
		}

		@Override
		public boolean equals(Object other) {
			return (this == other ||
					(other instanceof DynamicAdvisedInterceptor &&
							this.advised.equals(((DynamicAdvisedInterceptor) other).advised)));
		}

		/**
		 * CGLIB uses this to drive proxy creation.
		 */
		@Override
		public int hashCode() {
			return this.advised.hashCode();
		}

		protected Object getTarget() throws Exception {
			return this.advised.getTargetSource().getTarget();
		}

		protected void releaseTarget(Object target) throws Exception {
			this.advised.getTargetSource().releaseTarget(target);
		}
	}


	/**
	 * Implementation of AOP Alliance MethodInvocation used by this AOP proxy.
	 */
	private static class CglibMethodInvocation extends ReflectiveMethodInvocation {

		private final MethodProxy methodProxy;

		private boolean protectedMethod;

		public CglibMethodInvocation(Object proxy, Object target, Method method, Object[] arguments,
				Class<?> targetClass, List<Object> interceptorsAndDynamicMethodMatchers, MethodProxy methodProxy) {
			super(proxy, target, method, arguments, targetClass, interceptorsAndDynamicMethodMatchers);
			this.methodProxy = methodProxy;
			this.protectedMethod = Modifier.isProtected(method.getModifiers());
		}

		/**
		 * Gives a marginal performance improvement versus using reflection to
		 * invoke the target when invoking public methods.
		 */
		@Override
		protected Object invokeJoinpoint() throws Throwable {
			if (this.protectedMethod) {
				return super.invokeJoinpoint();
			}
			else {
				return this.methodProxy.invoke(this.target, this.arguments);
			}
		}
	}


	/**
	 * CallbackFilter to assign Callbacks to methods.
	 */
	private static class ProxyCallbackFilter implements CallbackFilter {

		private final AdvisedSupport advised;

		private final Map<String, Integer> fixedInterceptorMap;

		private final int fixedInterceptorOffset;

		public ProxyCallbackFilter(AdvisedSupport advised, Map<String, Integer> fixedInterceptorMap, int fixedInterceptorOffset) {
			this.advised = advised;
			this.fixedInterceptorMap = fixedInterceptorMap;
			this.fixedInterceptorOffset = fixedInterceptorOffset;
		}

		/**
		 * Implementation of CallbackFilter.accept() to return the index of the
		 * callback we need.
		 * <p>The callbacks for each proxy are built up of a set of fixed callbacks
		 * for general use and then a set of callbacks that are specific to a method
		 * for use on static targets with a fixed advice chain.
		 * <p>The callback used is determined thus:
		 * <dl>
		 * <dt>For exposed proxies</dt>
		 * <dd>Exposing the proxy requires code to execute before and after the
		 * method/chain invocation. This means we must use
		 * DynamicAdvisedInterceptor, since all other interceptors can avoid the
		 * need for a try/catch block</dd>
		 * <dt>For Object.finalize():</dt>
		 * <dd>No override for this method is used.</dd>
		 * <dt>For equals():</dt>
		 * <dd>The EqualsInterceptor is used to redirect equals() calls to a
		 * special handler to this proxy.</dd>
		 * <dt>For methods on the Advised class:</dt>
		 * <dd>the AdvisedDispatcher is used to dispatch the call directly to
		 * the target</dd>
		 * <dt>For advised methods:</dt>
		 * <dd>If the target is static and the advice chain is frozen then a
		 * FixedChainStaticTargetInterceptor specific to the method is used to
		 * invoke the advice chain. Otherwise a DyanmicAdvisedInterceptor is
		 * used.</dd>
		 * <dt>For non-advised methods:</dt>
		 * <dd>Where it can be determined that the method will not return {@code this}
		 * or when {@code ProxyFactory.getExposeProxy()} returns {@code false},
		 * then a Dispatcher is used. For static targets, the StaticDispatcher is used;
		 * and for dynamic targets, a DynamicUnadvisedInterceptor is used.
		 * If it possible for the method to return {@code this} then a
		 * StaticUnadvisedInterceptor is used for static targets - the
		 * DynamicUnadvisedInterceptor already considers this.</dd>
		 * </dl>
		 */
		public int accept(Method method) {
			if (AopUtils.isFinalizeMethod(method)) {
				logger.debug("Found finalize() method - using NO_OVERRIDE");
				return NO_OVERRIDE;
			}
			if (!this.advised.isOpaque() && method.getDeclaringClass().isInterface() &&
					method.getDeclaringClass().isAssignableFrom(Advised.class)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Method is declared on Advised interface: " + method);
				}
				return DISPATCH_ADVISED;
			}
			// We must always proxy equals, to direct calls to this.
			if (AopUtils.isEqualsMethod(method)) {
				logger.debug("Found 'equals' method: " + method);
				return INVOKE_EQUALS;
			}
			// We must always calculate hashCode based on the proxy.
			if (AopUtils.isHashCodeMethod(method)) {
				logger.debug("Found 'hashCode' method: " + method);
				return INVOKE_HASHCODE;
			}
			Class<?> targetClass = this.advised.getTargetClass();
			// Proxy is not yet available, but that shouldn't matter.
			List<?> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
			boolean haveAdvice = !chain.isEmpty();
			boolean exposeProxy = this.advised.isExposeProxy();
			boolean isStatic = this.advised.getTargetSource().isStatic();
			boolean isFrozen = this.advised.isFrozen();
			if (haveAdvice || !isFrozen) {
				// If exposing the proxy, then AOP_PROXY must be used.
				if (exposeProxy) {
					if (logger.isDebugEnabled()) {
						logger.debug("Must expose proxy on advised method: " + method);
					}
					return AOP_PROXY;
				}
				String key = method.toString();
				// Check to see if we have fixed interceptor to serve this method.
				// Else use the AOP_PROXY.
				if (isStatic && isFrozen && this.fixedInterceptorMap.containsKey(key)) {
					if (logger.isDebugEnabled()) {
						logger.debug("Method has advice and optimisations are enabled: " + method);
					}
					// We know that we are optimising so we can use the
					// FixedStaticChainInterceptors.
					int index = this.fixedInterceptorMap.get(key);
					return (index + this.fixedInterceptorOffset);
				}
				else {
					if (logger.isDebugEnabled()) {
						logger.debug("Unable to apply any optimisations to advised method: " + method);
					}
					return AOP_PROXY;
				}
			}
			else {
				// See if the return type of the method is outside the class hierarchy
				// of the target type. If so we know it never needs to have return type
				// massage and can use a dispatcher.
				// If the proxy is being exposed, then must use the interceptor the
				// correct one is already configured. If the target is not static cannot
				// use a Dispatcher because the target can not then be released.
				if (exposeProxy || !isStatic) {
					return INVOKE_TARGET;
				}
				Class<?> returnType = method.getReturnType();
				if (targetClass == returnType) {
					if (logger.isDebugEnabled()) {
						logger.debug("Method " + method +
								"has return type same as target type (may return this) - using INVOKE_TARGET");
					}
					return INVOKE_TARGET;
				}
				else if (returnType.isPrimitive() || !returnType.isAssignableFrom(targetClass)) {
					if (logger.isDebugEnabled()) {
						logger.debug("Method " + method +
								" has return type that ensures this cannot be returned- using DISPATCH_TARGET");
					}
					return DISPATCH_TARGET;
				}
				else {
					if (logger.isDebugEnabled()) {
						logger.debug("Method " + method +
								"has return type that is assignable from the target type (may return this) - " +
								"using INVOKE_TARGET");
					}
					return INVOKE_TARGET;
				}
			}
		}

		@Override
		public boolean equals(Object other) {
			if (other == this) {
				return true;
			}
			if (!(other instanceof ProxyCallbackFilter)) {
				return false;
			}
			ProxyCallbackFilter otherCallbackFilter = (ProxyCallbackFilter) other;
			AdvisedSupport otherAdvised = otherCallbackFilter.advised;
			if (this.advised == null || otherAdvised == null) {
				return false;
			}
			if (this.advised.isFrozen() != otherAdvised.isFrozen()) {
				return false;
			}
			if (this.advised.isExposeProxy() != otherAdvised.isExposeProxy()) {
				return false;
			}
			if (this.advised.getTargetSource().isStatic() != otherAdvised.getTargetSource().isStatic()) {
				return false;
			}
			if (!AopProxyUtils.equalsProxiedInterfaces(this.advised, otherAdvised)) {
				return false;
			}
			// Advice instance identity is unimportant to the proxy class:
			// All that matters is type and ordering.
			Advisor[] thisAdvisors = this.advised.getAdvisors();
			Advisor[] thatAdvisors = otherAdvised.getAdvisors();
			if (thisAdvisors.length != thatAdvisors.length) {
				return false;
			}
			for (int i = 0; i < thisAdvisors.length; i++) {
				Advisor thisAdvisor = thisAdvisors[i];
				Advisor thatAdvisor = thatAdvisors[i];
				if (!equalsAdviceClasses(thisAdvisor, thatAdvisor)) {
					return false;
				}
				if (!equalsPointcuts(thisAdvisor, thatAdvisor)) {
					return false;
				}
			}
			return true;
		}

		private boolean equalsAdviceClasses(Advisor a, Advisor b) {
			Advice aa = a.getAdvice();
			Advice ba = b.getAdvice();
			if (aa == null || ba == null) {
				return (aa == ba);
			}
			return aa.getClass().equals(ba.getClass());
		}

		private boolean equalsPointcuts(Advisor a, Advisor b) {
			// If only one of the advisor (but not both) is PointcutAdvisor, then it is a mismatch.
			// Takes care of the situations where an IntroductionAdvisor is used (see SPR-3959).
			return (!(a instanceof PointcutAdvisor) ||
					(b instanceof PointcutAdvisor &&
							ObjectUtils.nullSafeEquals(((PointcutAdvisor) a).getPointcut(), ((PointcutAdvisor) b).getPointcut())));
		}

		@Override
		public int hashCode() {
			int hashCode = 0;
			Advisor[] advisors = this.advised.getAdvisors();
			for (Advisor advisor : advisors) {
				Advice advice = advisor.getAdvice();
				if (advice != null) {
					hashCode = 13 * hashCode + advice.getClass().hashCode();
				}
			}
			hashCode = 13 * hashCode + (this.advised.isFrozen() ? 1 : 0);
			hashCode = 13 * hashCode + (this.advised.isExposeProxy() ? 1 : 0);
			hashCode = 13 * hashCode + (this.advised.isOptimize() ? 1 : 0);
			hashCode = 13 * hashCode + (this.advised.isOpaque() ? 1 : 0);
			return hashCode;
		}
	}

}
