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<meta name="keywords" content="Java,Java SE,Java基础,Java教程,Java程序员进阶之路,Java进阶之路,Java入门,教程,JavaSocket,java网络编程,socket,网络编程,java socket,java 网络编程"><meta property="og:url" content="https://tobebetterjavaer.com/socket/socket.html"><meta property="og:site_name" content="Java程序员进阶之路"><meta property="og:title" content="Java Socket：飞鸽传书的网络套接字"><meta property="og:description" content="描述：本文详细介绍了Java网络编程中的核心概念——套接字Socket。阐述了套接字的基本原理、Java中Socket类的使用方法及示例。本文旨在帮助读者了解套接字Socket的实际应用，以及如何在Java中实现网络编程的基本功能。"><meta property="og:type" content="article"><meta property="og:locale" content="zh-CN"><meta property="og:updated_time" content="2023-04-24T02:39:04.000Z"><meta property="article:tag" content="Java网络编程"><meta property="article:modified_time" content="2023-04-24T02:39:04.000Z"><script type="application/ld+json">{"@context":"https://schema.org","@type":"Article","headline":"Java Socket：飞鸽传书的网络套接字","image":[""],"dateModified":"2023-04-24T02:39:04.000Z","author":[]}</script><meta name="robots" content="all"><meta name="author" content="沉默王二"><meta http-equiv="Cache-Control" content="no-cache, no-store, must-revalidate"><meta http-equiv="Pragma" content="no-cache"><meta http-equiv="Expires" content="0"><meta name="apple-mobile-web-app-capable" content="yes"><script>
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99.2-25.6 0 0 6.4-12.8 9.6-19.2 54.4-105.6 275.2-524.8 288-553.6 6.4-19.2-3.2-32-19.2-32C777.6 76.8 771.2 80 764.8 86.4z"></path></svg><div class="outlook-dropdown"><!----></div></button></div><div id="docsearch-container"></div><!--[--><!----><!--]--><button class="toggle-navbar-button" aria-label="Toggle Navbar" aria-expanded="false" aria-controls="nav-screen"><span class="button-container"><span class="button-top"></span><span class="button-middle"></span><span class="button-bottom"></span></span></button></div></header><!----><!--]--><!----><div class="toggle-sidebar-wrapper"><span class="arrow start"></span></div><aside class="sidebar" id="sidebar"><!--[--><!----><!--]--><ul class="sidebar-links"><li><!--[--><a href="/home.html" class="nav-link sidebar-link sidebar-page" aria-label="一、前言"><!---->一、前言<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">二、Java基础</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.1 Java概述及环境配置</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.2 Java语法基础</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.3 数组&字符串</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.4 面向对象编程</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.5 集合框架（容器）</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.6 Java IO</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.7 异常处理</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.8 常用工具类</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.9 Java新特性</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable active"><!----><span class="title">2.10 网络编程</span><span class="arrow down"></span></button><ul class="sidebar-links"><li><!--[--><a href="/socket/network-base.html" class="nav-link sidebar-link sidebar-page" aria-label="了解网络编程的基础知识"><!---->了解网络编程的基础知识<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li><li><!--[--><a aria-current="page" href="/socket/socket.html" class="router-link-active router-link-exact-active nav-link active sidebar-link sidebar-page active" aria-label="网络编程的核心套接字Socket"><!---->网络编程的核心套接字Socket<!----></a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header"><a aria-current="page" href="/socket/socket.html#_01、ping-与-telnet" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="01、ping 与 telnet"><!---->01、ping 与 telnet<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/socket/socket.html#_02、socket-实例" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="02、Socket 实例"><!---->02、Socket 实例<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/socket/socket.html#_03、serversocket-实例" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="03、ServerSocket 实例"><!---->03、ServerSocket 实例<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/socket/socket.html#_04、为多个客户端服务" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="04、为多个客户端服务"><!---->04、为多个客户端服务<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/socket/socket.html#_05、加入多线程" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="05、加入多线程"><!---->05、加入多线程<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/socket/socket.html#_08、datagramsocket-实例" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="08、DatagramSocket 实例"><!---->08、DatagramSocket 实例<!----></a><ul class="sidebar-sub-headers"></ul></li><li class="sidebar-sub-header"><a aria-current="page" href="/socket/socket.html#_07、最后" class="router-link-active router-link-exact-active nav-link sidebar-link heading" aria-label="07、最后"><!---->07、最后<!----></a><ul class="sidebar-sub-headers"></ul></li></ul><!--]--></li><li><!--[--><a href="/socket/http.html" class="nav-link sidebar-link sidebar-page" aria-label="用Socket实现一个HTTP服务器"><!---->用Socket实现一个HTTP服务器<!----></a><ul class="sidebar-sub-headers"></ul><!--]--></li></ul></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.11 NIO</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.12 Java重要知识点</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.13 并发编程</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">2.14 JVM</span><span class="arrow end"></span></button><!----></section></li></ul></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">三、Java进阶</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">四、数据库</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">五、计算机基础</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">六、求职面试</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">七、学习建议</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">八、知识库搭建</span><span class="arrow end"></span></button><!----></section></li><li><section class="sidebar-group"><button class="sidebar-heading clickable"><!----><span class="title">九、联系作者</span><span class="arrow end"></span></button><!----></section></li></ul><!--[--><!----><!--]--></aside><!--[--><main class="page" id="main-content"><!--[--><!----><nav class="breadcrumb disable"></nav><div class="page-title"><h1><!---->Java Socket：飞鸽传书的网络套接字</h1><div class="page-info"><span class="page-author-info" aria-label="作者🖊" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon author-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="author icon"><path d="M649.6 633.6c86.4-48 147.2-144 147.2-249.6 0-160-128-288-288-288s-288 128-288 288c0 108.8 57.6 201.6 147.2 249.6-121.6 48-214.4 153.6-240 288-3.2 9.6 0 19.2 6.4 25.6 3.2 9.6 12.8 12.8 22.4 12.8h704c9.6 0 19.2-3.2 25.6-12.8 6.4-6.4 9.6-16 6.4-25.6-25.6-134.4-121.6-240-243.2-288z"></path></svg><span><a class="page-author-item" href="/about-the-author/" target="_blank" rel="noopener noreferrer">沉默王二</a></span><span property="author" content="沉默王二"></span></span><!----><span class="page-date-info" aria-label="写作日期📅" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon calendar-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="calendar icon"><path d="M716.4 110.137c0-18.753-14.72-33.473-33.472-33.473-18.753 0-33.473 14.72-33.473 33.473v33.473h66.993v-33.473zm-334.87 0c0-18.753-14.72-33.473-33.473-33.473s-33.52 14.72-33.52 33.473v33.473h66.993v-33.473zm468.81 33.52H716.4v100.465c0 18.753-14.72 33.473-33.472 33.473a33.145 33.145 0 01-33.473-33.473V143.657H381.53v100.465c0 18.753-14.72 33.473-33.473 33.473a33.145 33.145 0 01-33.473-33.473V143.657H180.6A134.314 134.314 0 0046.66 277.595v535.756A134.314 134.314 0 00180.6 947.289h669.74a134.36 134.36 0 00133.94-133.938V277.595a134.314 134.314 0 00-133.94-133.938zm33.473 267.877H147.126a33.145 33.145 0 01-33.473-33.473c0-18.752 14.72-33.473 33.473-33.473h736.687c18.752 0 33.472 14.72 33.472 33.473a33.145 33.145 0 01-33.472 33.473z"></path></svg><span><!----></span><meta property="datePublished" content="2022-08-27T03:31:28.000Z"></span><span class="page-category-info" aria-label="分类🌈" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon category-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="category icon"><path d="M148.41 106.992h282.176c22.263 0 40.31 18.048 40.31 40.31V429.48c0 22.263-18.047 40.31-40.31 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role="navigation">Java核心</span><meta property="articleSection" content="Java核心"></span><span class="page-tag-info" aria-label="标签🏷" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon tag-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="tag icon"><path d="M939.902 458.563L910.17 144.567c-1.507-16.272-14.465-29.13-30.737-30.737L565.438 84.098h-.402c-3.215 0-5.726 1.005-7.634 2.913l-470.39 470.39a10.004 10.004 0 000 14.164l365.423 365.424c1.909 1.908 4.42 2.913 7.132 2.913s5.223-1.005 7.132-2.913l470.39-470.39c2.01-2.11 3.014-5.023 2.813-8.036zm-240.067-72.121c-35.458 0-64.286-28.828-64.286-64.286s28.828-64.285 64.286-64.285 64.286 28.828 64.286 64.285-28.829 64.286-64.286 64.286z"></path></svg><span class="page-tag-item tag1 clickable" role="navigation">Java网络编程</span><meta property="keywords" content="Java网络编程"></span><span class="page-word-info" aria-label="字数🔠" data-balloon-pos="down"><svg xmlns="http://www.w3.org/2000/svg" class="icon word-icon" 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11.651-7.638 19.03v5.825h566.49v-5.825c0-7.379-2.849-13.981-7.509-18.9-5.049-193.016-97.867-351.985-220.2-389.527 123.24-37.67 216.446-198.453 220.588-392.892zM531.16 450.445v352.632c117.674 1.553 211.787 40.778 211.787 88.676H304.097c0-48.286 95.149-87.382 213.728-88.676V450.445c-93.077-3.107-167.901-81.297-167.901-177.093 0-8.803 6.99-15.793 15.793-15.793 8.803 0 15.794 6.99 15.794 15.793 0 80.261 63.69 145.635 142.01 145.635s142.011-65.374 142.011-145.635c0-8.803 6.99-15.793 15.794-15.793s15.793 6.99 15.793 15.793c0 95.019-73.789 172.82-165.96 177.093z"></path></svg><span>大约 10 分钟</span><meta property="timeRequired" content="PT10M"></span></div><hr></div><div class="toc-place-holder"><aside id="toc"><!--[--><!----><!--]--><div class="toc-header">此页内容<button class="print-button" title="print"><svg xmlns="http://www.w3.org/2000/svg" class="icon print-icon" viewBox="0 0 1024 1024" fill="currentColor" aria-label="print icon"><path d="M819.2 364.8h-44.8V128c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v236.8h-44.8C145.067 364.8 96 413.867 96 473.6v192c0 59.733 49.067 108.8 108.8 108.8h44.8V896c0 17.067 14.933 32 32 32h460.8c17.067 0 32-14.933 32-32V774.4h44.8c59.733 0 108.8-49.067 108.8-108.8v-192c0-59.733-49.067-108.8-108.8-108.8zM313.6 160h396.8v204.8H313.6V160zm396.8 704H313.6V620.8h396.8V864zM864 665.6c0 25.6-19.2 44.8-44.8 44.8h-44.8V588.8c0-17.067-14.933-32-32-32H281.6c-17.067 0-32 14.933-32 32v121.6h-44.8c-25.6 0-44.8-19.2-44.8-44.8v-192c0-25.6 19.2-44.8 44.8-44.8h614.4c25.6 0 44.8 19.2 44.8 44.8v192z"></path></svg></button></div><div class="toc-wrapper"><ul class="toc-list"><!--[--><li class="toc-item"><a aria-current="page" href="/socket/socket.html#_01、ping-与-telnet" class="router-link-active router-link-exact-active toc-link level3">01、ping 与 telnet</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/socket/socket.html#_02、socket-实例" class="router-link-active router-link-exact-active toc-link level3">02、Socket 实例</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/socket/socket.html#_03、serversocket-实例" class="router-link-active router-link-exact-active toc-link level3">03、ServerSocket 实例</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/socket/socket.html#_04、为多个客户端服务" class="router-link-active router-link-exact-active toc-link level3">04、为多个客户端服务</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/socket/socket.html#_05、加入多线程" class="router-link-active router-link-exact-active toc-link level3">05、加入多线程</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/socket/socket.html#_08、datagramsocket-实例" class="router-link-active router-link-exact-active toc-link level3">08、DatagramSocket 实例</a></li><!----><!--]--><!--[--><li class="toc-item"><a aria-current="page" href="/socket/socket.html#_07、最后" class="router-link-active router-link-exact-active toc-link level3">07、最后</a></li><!----><!--]--></ul></div><!--[--><!----><!--]--></aside></div><!----><div class="theme-hope-content"><h1 id="_11-2-网络编程的核心套接字socket" tabindex="-1"><a class="header-anchor" href="#_11-2-网络编程的核心套接字socket" aria-hidden="true">#</a> 11.2 网络编程的核心套接字Socket</h1><p>在古代，由于通信不便利，一些聪明的人就利用鸽子会飞且飞得比较快、会辨认方向的优点，对其进行了驯化，用来进行消息的传递——也就是所谓的“飞鸽传书”。而在 Java 中，网络套接字（Socket）扮演了同样的角色。</p><figure><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/socket/socket-a1a012de-33e5-424a-a4cf-bd929cd60200.jpg" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>套接字（Socket）是一个抽象层，应用程序可以通过它发送或接收数据；就像操作文件那样可以打开、读写和关闭。套接字允许应用程序将 I/O 应用于网络中，并与其他应用程序进行通信。网络套接字是 IP 地址与端口的组合。</p><h3 id="_01、ping-与-telnet" tabindex="-1"><a class="header-anchor" href="#_01、ping-与-telnet" aria-hidden="true">#</a> 01、ping 与 telnet</h3><p>“老王啊，能不能帮我看一下这个问题呢，明明本地可以进行网络通信，可等我部署到服务器上时就通信不了了，搞了半天也不知道什么原因，我看代码是没有问题的。”小二的语气中充满了沮丧。</p><p>“ping 过吗？或者 telnet 了吗？”老王头都没回，冷冰冰地扔出去了这句话。</p><p>“哦，我去试试。”小二心头掠过一丝愧疚。</p><p>ping 与 telnet 这两个命令，对调试网络程序有着非常大的帮助。</p><p>ping，一种计算机网络工具，用来测试数据包能否透过 IP 协议到达特定主机。ping 会向目标主机发出一个 ICMP 的请求回显数据包，并等待接收回显响应数据包。</p><p>例如，我们 ping 一下博客园。截图如下。</p><figure><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/socket/socket-ce54bbbe-3627-4af4-9f9c-4c041a7ef2a7.jpg" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>telnet，Internet 远程登录服务的标准协议和主要方式，可以让我们坐在家里的计算机面前，登录到另一台远在天涯海角的远程计算机上。</p><figure><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/socket/socket-f94e1fa5-16d0-4414-9a53-a2aa43b2a512.jpg" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>在 Windows 系统中，telnet 一般是默认安装的，但未激活（可以在控制面板中激活它）。</p><p>例如，我们 telnet 一下火（shui）土（mu）社区。截图如下。</p><figure><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/socket/socket-9d7051d9-e7de-48a8-9b28-b482d84f56c9.jpg" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>使用 telnet 登录远程计算机时，需要远程计算机上运行一个服务，它一直不停地等待那些希望和它进行连接的网络请求；当接收到一个客户端的网络连接时，它便唤醒正在监听网络连接请求的服务器进程，并为两者建立连接。连接会一直保持，直到某一方中止。</p><p>不过，需要注意的是，telnet 在格外重视安全的现代网络技术中并不受到重用。因为 telnet 是一个明文传输协议，用户的所有内容（包括用户名和密码）都没有经过加密，安全隐患非常大。</p><h3 id="_02、socket-实例" tabindex="-1"><a class="header-anchor" href="#_02、socket-实例" aria-hidden="true">#</a> 02、Socket 实例</h3><p>不知道你有没有体验一下 telnet 火土社区的那条命令，结果非常有趣。我们也可以通过 Java 的客户端套接字（Socket）实现，代码示例如下。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">try</span> <span class="token punctuation">(</span><span class="token class-name">Socket</span> socket <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Socket</span><span class="token punctuation">(</span><span class="token string">"bbs.newsmth.net"</span><span class="token punctuation">,</span> <span class="token number">23</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">InputStream</span> is <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Scanner</span> scanner <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span>is<span class="token punctuation">,</span> <span class="token string">"gbk"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span>scanner<span class="token punctuation">.</span><span class="token function">hasNextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> line <span class="token operator">=</span> scanner<span class="token punctuation">.</span><span class="token function">nextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">UnknownHostException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>1）建立套接字连接非常简单，只需要一行代码：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">Socket</span> socket <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Socket</span><span class="token punctuation">(</span>host<span class="token punctuation">,</span> port<span class="token punctuation">)</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>host 为主机名，port 为端口号（23 为默认的 telnet 端口号）。如果无法确定主机的 IP 地址，则抛出 <code>UnknownHostException</code> 异常；如果在创建套接字时发生 IO 错误，则抛出 <code>IOException</code> 异常。</p><p>需要注意的是，套接字在建立的时候，如果远程主机不可访问，这段代码就会阻塞很长时间，直到底层操作系统的限制而抛出异常。所以一般会在套接字建立后设置一个超时时间。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">Socket</span> socket <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Socket</span><span class="token punctuation">(</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
socket<span class="token punctuation">.</span><span class="token function">setSoTimeout</span><span class="token punctuation">(</span><span class="token number">10000</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 单位为毫秒</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div></div></div><p>2）套接字连接成功后，可以通过 <code>java.net.Socket</code> 类的 <code>getInputStream()</code> 方法获取输入流。有了 <code>InputStream</code> 对象后，可以借助文本扫描器类（Scanner）将其中的内容打印出来。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">InputStream</span> is <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Scanner</span> scanner <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span>is<span class="token punctuation">,</span> <span class="token string">"gbk"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span>scanner<span class="token punctuation">.</span><span class="token function">hasNextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> line <span class="token operator">=</span> scanner<span class="token punctuation">.</span><span class="token function">nextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>部分结果（完整结果自己亲手实践一下哦）如下图所示：</p><figure><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/socket/socket-6b60e4b2-14d0-4d95-bb5c-146bc6a06147.jpg" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><h3 id="_03、serversocket-实例" tabindex="-1"><a class="header-anchor" href="#_03、serversocket-实例" aria-hidden="true">#</a> 03、ServerSocket 实例</h3><p>接下来，我们模拟一个远程服务，通过 <code>java.net.ServerSocket</code> 实现。代码示例如下。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">try</span> <span class="token punctuation">(</span><span class="token class-name">ServerSocket</span> server <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ServerSocket</span><span class="token punctuation">(</span><span class="token number">8888</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Socket</span> socket <span class="token operator">=</span> server<span class="token punctuation">.</span><span class="token function">accept</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">InputStream</span> is <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">OutputStream</span> os <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getOutputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Scanner</span> scanner <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span>is<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">PrintWriter</span> pw <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">PrintWriter</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">OutputStreamWriter</span><span class="token punctuation">(</span>os<span class="token punctuation">,</span> <span class="token string">"gbk"</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
pw<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"你好啊，欢迎关注「沉默王二」 公众号，回复关键字「2048」 领取程序员进阶必读资料包"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">boolean</span> done <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token operator">!</span>done <span class="token operator">&&</span> scanner<span class="token punctuation">.</span><span class="token function">hasNextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> line <span class="token operator">=</span> scanner<span class="token punctuation">.</span><span class="token function">nextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token string">"2048"</span><span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
done <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">UnknownHostException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>1）建立服务器端的套接字也比较简单，只需要指定一个能够独占的端口号就可以了（0~1023 这些端口都已经被系统预留了）。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">ServerSocket</span> server <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ServerSocket</span><span class="token punctuation">(</span><span class="token number">8888</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div></div></div><p>2）调用 ServerSocket 对象的 <code>accept()</code> 等待客户端套接字的连接请求。一旦监听到客户端的套接字请求，就会返回一个表示连接已建立的 Socket 对象，可以从中获取到输入流和输出流。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">Socket</span> socket <span class="token operator">=</span> server<span class="token punctuation">.</span><span class="token function">accept</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">InputStream</span> is <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">OutputStream</span> os <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getOutputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>客户端套接字发送的所有信息都会包裹在服务器端套接字的输入流中；而服务器端套接字发送的所有信息都会包裹在客户端套接字的输出流中。</p><p>3）服务器端可以通过以下代码向客户端发送消息。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">PrintWriter</span> pw <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">PrintWriter</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">OutputStreamWriter</span><span class="token punctuation">(</span>os<span class="token punctuation">,</span> <span class="token string">"gbk"</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
pw<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"你好啊，欢迎关注「沉默王二」 公众号，回复关键字「2048」 领取程序员进阶必读资料包"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div></div></div><p>4）服务器端可以通过以下代码读取客户端发送过来的消息。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token class-name">Scanner</span> scanner <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span>is<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">boolean</span> done <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token operator">!</span>done <span class="token operator">&&</span> scanner<span class="token punctuation">.</span><span class="token function">hasNextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> line <span class="token operator">=</span> scanner<span class="token punctuation">.</span><span class="token function">nextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token string">"2048"</span><span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>line<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
done <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>运行该服务后，可以通过 <code>telnet localhost 8888</code> 命令连接该远程服务，不出所料，你将会看到以下信息。</p><figure><img src="https://cdn.tobebetterjavaer.com/tobebetterjavaer/images/socket/socket-fac025fa-8cbf-448d-8a6d-cd8993ba87f4.jpg" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><p>PS：可以在当前命令窗口中输入 2048，服务端收到该消息后会中断该套接字连接（当前窗口会显示“遗失对主机的连接”）。</p><h3 id="_04、为多个客户端服务" tabindex="-1"><a class="header-anchor" href="#_04、为多个客户端服务" aria-hidden="true">#</a> 04、为多个客户端服务</h3><p>非常遗憾的是，上面的例子中，服务器端只能为一个客户端服务——这不符合服务器端一对多的要求。</p><p>优化方案也非常简单（你应该也能想得到）：服务器端接收到客户端的套接字请求时，可以启动一个线程来处理，而主程序继续等待下一个连接。代码示例如下。</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">try</span> <span class="token punctuation">(</span><span class="token class-name">ServerSocket</span> server <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ServerSocket</span><span class="token punctuation">(</span><span class="token number">8888</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">Socket</span> socket <span class="token operator">=</span> server<span class="token punctuation">.</span><span class="token function">accept</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Thread</span> thread <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Thread</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Runnable</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Override</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">// 套接字处理程序</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
thread<span class="token punctuation">.</span><span class="token function">start</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>线程内部（<code>run(){}</code> 方法里）用来处理套接字，代码示例如下：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">try</span> <span class="token punctuation">{</span>
<span class="token class-name">InputStream</span> is <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">OutputStream</span> os <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getOutputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">Scanner</span> scanner <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span>is<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// 其他代码省略</span>
<span class="token comment">// 向客户端发送消息</span>
<span class="token comment">// 读取客户端发送过来的消息</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">finally</span> <span class="token punctuation">{</span>
<span class="token keyword">try</span> <span class="token punctuation">{</span>
socket<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>服务器端代码优化后重新运行，你就可以通过 telnet 命令测试了。打开一个命令行窗口输入 <code>telnet localhost 8888</code>，再打开一个新的命令行窗口输入 <code>telnet localhost 8888</code>，多个窗口都可以和服务器端进行通信，除非服务器端代码中断运行。</p><h3 id="_05、加入多线程" tabindex="-1"><a class="header-anchor" href="#_05、加入多线程" aria-hidden="true">#</a> 05、加入多线程</h3><p><a href="https://tobebetterjavaer.com/thread/wangzhe-thread.html" target="_blank" rel="noopener noreferrer">多线程<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg><span class="external-link-icon-sr-only">open in new window</span></span></a>我们后面会详细讲，这里就主要是写个例子，好让大家感觉更有趣一些，其实也非常简单。</p><p>来看服务端：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token operator">*</span></span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>net<span class="token punctuation">.</span></span><span class="token class-name">ServerSocket</span></span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>net<span class="token punctuation">.</span></span><span class="token class-name">Socket</span></span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">MultiThreadedServer</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token keyword">int</span> port <span class="token operator">=</span> <span class="token number">12345</span><span class="token punctuation">;</span>
<span class="token class-name">ServerSocket</span> serverSocket <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ServerSocket</span><span class="token punctuation">(</span>port<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Server is listening on port "</span> <span class="token operator">+</span> port<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">Socket</span> socket <span class="token operator">=</span> serverSocket<span class="token punctuation">.</span><span class="token function">accept</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Client connected"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">ClientHandler</span><span class="token punctuation">(</span>socket<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">start</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">class</span> <span class="token class-name">ClientHandler</span> <span class="token keyword">extends</span> <span class="token class-name">Thread</span> <span class="token punctuation">{</span>
<span class="token keyword">private</span> <span class="token class-name">Socket</span> socket<span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token class-name">ClientHandler</span><span class="token punctuation">(</span><span class="token class-name">Socket</span> socket<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">this</span><span class="token punctuation">.</span>socket <span class="token operator">=</span> socket<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">try</span> <span class="token punctuation">{</span>
<span class="token class-name">InputStream</span> input <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">BufferedReader</span> reader <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">InputStreamReader</span><span class="token punctuation">(</span>input<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">OutputStream</span> output <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getOutputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">PrintWriter</span> writer <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">PrintWriter</span><span class="token punctuation">(</span>output<span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> line<span class="token punctuation">;</span>
<span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>line <span class="token operator">=</span> reader<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Received: "</span> <span class="token operator">+</span> line<span class="token punctuation">)</span><span class="token punctuation">;</span>
writer<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Server: "</span> <span class="token operator">+</span> line<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
socket<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Client disconnected"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>在这个示例中，我们使用了一个 ClientHandler 类，该类继承自 Thread 类。这使得每个客户端连接都可以在单独的线程中处理，从而允许服务器同时处理多个客户端连接。当一个新客户端连接到服务器时，服务器会创建一个新的 ClientHandler 对象，并使用 <code>start()</code> 方法启动线程。ClientHandler 类的 <code>run()</code> 方法包含处理客户端请求的逻辑。</p><p>来看客户端代码：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token operator">*</span></span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>net<span class="token punctuation">.</span></span><span class="token class-name">Socket</span></span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Client</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> hostname <span class="token operator">=</span> <span class="token string">"localhost"</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> port <span class="token operator">=</span> <span class="token number">12345</span><span class="token punctuation">;</span>
<span class="token class-name">Socket</span> socket <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Socket</span><span class="token punctuation">(</span>hostname<span class="token punctuation">,</span> port<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Connected to the server"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">InputStream</span> input <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getInputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">BufferedReader</span> reader <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">InputStreamReader</span><span class="token punctuation">(</span>input<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">OutputStream</span> output <span class="token operator">=</span> socket<span class="token punctuation">.</span><span class="token function">getOutputStream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">PrintWriter</span> writer <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">PrintWriter</span><span class="token punctuation">(</span>output<span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
writer<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Hello, server!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> response <span class="token operator">=</span> reader<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Server response: "</span> <span class="token operator">+</span> response<span class="token punctuation">)</span><span class="token punctuation">;</span>
socket<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>启动服务器端，然后多启动几个客户端，就可以体验到交互的乐趣了。</p><figure><img src="https://cdn.tobebetterjavaer.com/stutymore/socket-20230330192826.png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><h3 id="_08、datagramsocket-实例" tabindex="-1"><a class="header-anchor" href="#_08、datagramsocket-实例" aria-hidden="true">#</a> 08、DatagramSocket 实例</h3><p>DatagramSocket 类是 Java 中实现 UDP 协议的核心类。与基于 TCP 的 Socket 和 ServerSocket 类不同，DatagramSocket 类提供了无连接的通信服务，发送和接收数据包。由于无需建立连接，UDP 通常比 TCP 更快，但可能不如 TCP 可靠。</p><p>以下是一个简单的 DatagramSocket 示例，展示了如何使用 UDP 协议在客户端和服务器之间发送和接收消息。</p><p>服务器端代码：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">IOException</span></span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>net<span class="token punctuation">.</span></span><span class="token class-name">DatagramPacket</span></span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>net<span class="token punctuation">.</span></span><span class="token class-name">DatagramSocket</span></span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">UDPServer</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token keyword">int</span> port <span class="token operator">=</span> <span class="token number">12345</span><span class="token punctuation">;</span>
<span class="token class-name">DatagramSocket</span> serverSocket <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">DatagramSocket</span><span class="token punctuation">(</span>port<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Server is listening on port "</span> <span class="token operator">+</span> port<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buffer <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token number">1024</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token class-name">DatagramPacket</span> packet <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">DatagramPacket</span><span class="token punctuation">(</span>buffer<span class="token punctuation">,</span> buffer<span class="token punctuation">.</span>length<span class="token punctuation">)</span><span class="token punctuation">;</span>
serverSocket<span class="token punctuation">.</span><span class="token function">receive</span><span class="token punctuation">(</span>packet<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> message <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>packet<span class="token punctuation">.</span><span class="token function">getData</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> packet<span class="token punctuation">.</span><span class="token function">getLength</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Received: "</span> <span class="token operator">+</span> message<span class="token punctuation">)</span><span class="token punctuation">;</span>
serverSocket<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>客户端代码：</p><div class="language-java line-numbers-mode" data-ext="java"><pre class="language-java"><code><span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">IOException</span></span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token import"><span class="token namespace">java<span class="token punctuation">.</span>net<span class="token punctuation">.</span></span><span class="token operator">*</span></span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">UDPClient</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{</span>
<span class="token class-name">String</span> hostname <span class="token operator">=</span> <span class="token string">"localhost"</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> port <span class="token operator">=</span> <span class="token number">12345</span><span class="token punctuation">;</span>
<span class="token class-name">InetAddress</span> address <span class="token operator">=</span> <span class="token class-name">InetAddress</span><span class="token punctuation">.</span><span class="token function">getByName</span><span class="token punctuation">(</span>hostname<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">DatagramSocket</span> clientSocket <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">DatagramSocket</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> message <span class="token operator">=</span> <span class="token string">"Hello, server!"</span><span class="token punctuation">;</span>
<span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buffer <span class="token operator">=</span> message<span class="token punctuation">.</span><span class="token function">getBytes</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">DatagramPacket</span> packet <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">DatagramPacket</span><span class="token punctuation">(</span>buffer<span class="token punctuation">,</span> buffer<span class="token punctuation">.</span>length<span class="token punctuation">,</span> address<span class="token punctuation">,</span> port<span class="token punctuation">)</span><span class="token punctuation">;</span>
clientSocket<span class="token punctuation">.</span><span class="token function">send</span><span class="token punctuation">(</span>packet<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Message sent"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
clientSocket<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre><div class="line-numbers" aria-hidden="true"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>在这个示例中，服务器端创建一个 DatagramSocket 对象并监听端口 12345。然后，它创建一个 DatagramPacket 对象，用于存储接收到的数据包。<code>serverSocket.receive(packet)</code> 方法阻塞，直到收到一个数据包。收到数据包后，服务器从数据包中提取并打印消息。</p><p>客户端首先解析服务器的 IP 地址，然后创建一个 DatagramSocket 对象。接着，客户端创建一个包含要发送消息的 DatagramPacket 对象，并指定目标地址和端口。最后，客户端通过调用 <code>clientSocket.send(packet)</code> 方法发送数据包。</p><p>运行结果如下所示：</p><figure><img src="https://cdn.tobebetterjavaer.com/stutymore/socket-20230330193654.png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><h3 id="_07、最后" tabindex="-1"><a class="header-anchor" href="#_07、最后" aria-hidden="true">#</a> 07、最后</h3><p>如今大多数基于网络的软件，如浏览器、即时通讯工具甚至是 P2P 下载都是基于 Socket 实现的，所以掌握 Java Socket 编程还是蛮有必要的。Socket 编程也比较有趣，很多初学者都会编写一两个基于“客户端-服务器端”的小程序来提高自己的编程水平，建议你也试一试。</p><hr><p>GitHub 上标星 7600+ 的开源知识库《<a href="https://github.com/itwanger/toBeBetterJavaer" target="_blank" rel="noopener noreferrer">二哥的 Java 进阶之路<span><svg class="external-link-icon" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path><polygon fill="currentColor" points="45.7,48.7 51.3,54.3 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