基于tomcat运行HTML5 WebSocket echo例子

jopen 8年前

一:概述

作为HTML5新特性之一的WebSocket组件,在实时性有一定要求的WEB应用开发中还是有一定用武之地,高版本的IE、Chrome、FF浏览器都支持Websocket,标准的Websocket通信是基于RFC6455实现服务器端与客户端握手与消息接发的。如果对Websocket通信不是太理解,可以查看RFC文档即可,简单说就是通过发送HTTP请求,实现双方握手,将无状态的HTTP通信协议进一步升级成有状态的通信协议,同时Websocket还支持子协议选项与安全传输。标准的websocket连接URL以ws开头,如果是基于TLS的则以wss开头。基于Websocket可以很方便的开发基于web聊天程序,各种网页消息通知与推送通知。

         如果非要扒一扒websocket的今生前世的话,还记得最早的基于HTTP轮询实现网页即时通信的方式,那种做法比较消耗资源、于是有人改进了编程CometD长连接方式,可是本质上还是换汤不换药,而websocket的出现正好解决了这些问题,但是很多浏览器的低版本还是不支持websocket,于是还催生了一些基于websocket理念实现的JS通信框架,其中学得比较像的有SockJS与socket.io,他们都号称支持websocket,然后如果浏览器端不支持原生的websocket,它们会自动启用fallback选项使用其它诸如ajax、Http轮询、长轮询/连接、甚至是flash的socket等机制实现模拟websocket的工作方式,但是他们最大的弊端是如果客户端使用了这些框架,服务器必须用它们,否则等待开发者就是一大堆无法回避的问题,同时很多都是无解的。主要原因在于它们实现自己的协议集,不照它们的格式处理数据没法玩。闲话说的有点多。

二 : 实现步骤

Tomcat7的高版本中实现了websocket服务器端RFC6455标准协议,可以跟浏览器端websocket进行通信,首先要做好如下几步:


1.      安装高版本JDK – JDK8

2.      安装tomcat 7.0.64

3.      在eclipse中建立一个动态的web项目

 

根据JSR标准,Java中实现websocket的标准接口可以基于注解方式,tomcat也搞好了,只有我们实现如下代码,即可创建一个websocket回声服务器:

 

package com.websocket.demo;    import java.io.IOException;  import java.nio.ByteBuffer;    import javax.websocket.OnMessage;  import javax.websocket.OnOpen;  import javax.websocket.Session;  import javax.websocket.server.ServerEndpoint;    @ServerEndpoint(value = "/echo")  public class EchoExample {      @OnMessage   public void echoTextMessage(Session session, String msg, boolean last) {    try {     if (session.isOpen()) {      System.out.println("received from client message = " + msg);      session.getBasicRemote().sendText(msg, last);     }    } catch (IOException e) {     try {      session.close();     } catch (IOException e1) {     }    }   }      @OnOpen      public void openConn(Session session) throws IOException {       session.getBasicRemote().sendText("hello web socket"); // means open it      }         @OnMessage      public void echoBinaryMessage(Session session, ByteBuffer bb, boolean last) {       System.out.println("send binary message...");          try {              if (session.isOpen()) {               System.out.println("byte buffer lenghth : " + bb.array().length);               System.out.println("byte buffer content: " + ((bb.array()[0]) & 0xff));               System.out.println("byte buffer content: " + ((bb.array()[1]) & 0xff));               System.out.println("byte buffer content: " + ((bb.array()[2]) & 0xff));                  session.getBasicRemote().sendBinary(bb, last);              }          } catch (IOException e) {              try {                  session.close();              } catch (IOException e1) {                  // Ignore              }          }      }    }


如何在tomcat中启动websocket服务器,首先需要在web.xml添加如下配置:


 <listener>    <listener-class>org.apache.tomcat.websocket.server.WsContextListener</listener-class>   </listener>

然后实现ServerApplicationConfig接口,实现如下:



/*   *   */  package com.config.websocket.client;    import java.util.HashSet;  import java.util.Set;    import javax.websocket.Endpoint;  import javax.websocket.server.ServerApplicationConfig;  import javax.websocket.server.ServerEndpointConfig;    public class ScanWebSocketSeverConfig implements ServerApplicationConfig {     @Override   public Set<ServerEndpointConfig> getEndpointConfigs(Set<Class<? extends Endpoint>> scanned) {      Set<ServerEndpointConfig> result = new HashSet<ServerEndpointConfig>();  /*  if (scanned.contains(EchoWsChatSever.class)) {     result.add(ServerEndpointConfig.Builder.create(EchoWsChatSever.class, "/echo").build());    }*/    return result;   }     @Override   public Set<Class<?>> getAnnotatedEndpointClasses(Set<Class<?>> scanned) {    Set<Class<?>> results = new HashSet<Class<?>>();    for (Class<?> clazz : scanned) {     if (clazz.getPackage().getName().startsWith("com.websocket.")) {      System.out.println("find end point : " + clazz.getName());      results.add(clazz);     }    }    return results;   }  }

创建网页echo.html,内容如下:



<html>  <head>  <title>Web Socket Echo Test</title>  <script>          var ws = null;    var count = 0;          function setConnected(connected) {              document.getElementById('connect').disabled = connected;              document.getElementById('disconnect').disabled = !connected;              document.getElementById('echo').disabled  = !connected;          }            function connect() {              var target = document.getElementById('target').value;              if (target == '') {                  alert('Please select server side connection implementation.');                  return;              }                if ('WebSocket' in window) {                  ws = new WebSocket(target);              } else if ('MozWebSocket' in window) {                  ws = new MozWebSocket(target);              } else {                  alert('WebSocket is not supported by this browser.');                  return;              }                            ws.onopen = function () {                  setConnected(true);                  log('Info: WebSocket connection opened.');              };              ws.onmessage = function (event) {                  log('Received: ' + event.data);                  if(event.data instanceof ArrayBuffer)                  {                   var bytes = new Uint8Array(event.data);                   alert(bytes.length + " : " + bytes[0]);                  }              };              ws.onclose = function (event) {                  setConnected(false);                  log('Info: WebSocket connection closed, Code: ' + event.code + (event.reason == "" ? "" : ", Reason: " + event.reason));              };                        }            function disconnect() {              if (ws != null) {               ws.doClose();               ws = null;              }              setConnected(false);          }            function echo() {              if (ws != null) {                  var message = document.getElementById('message').value;                  log('Sent: ' + message);                  ws.send(JSON.stringify({'textMessage': message}));                   count++              } else {                  alert('WebSocket connection not established, please connect.');              }          }            function log(message) {              var echomsg = document.getElementById('echomsg');              var p = document.createElement('p');              p.style.wordWrap = 'break-word';              p.appendChild(document.createTextNode(message));              echomsg.appendChild(p);              while (echomsg.childNodes.length > 25) {               echomsg.removeChild(console.firstChild);              }              echomsg.scrollTop = console.scrollHeight;          }            document.addEventListener("DOMContentLoaded", function() {              // Remove elements with "noscript" class - <noscript> is not allowed in XHTML              var noscripts = document.getElementsByClassName("noscript");              for (var i = 0; i < noscripts.length; i++) {                  noscripts[i].parentNode.removeChild(noscripts[i]);              }          }, false);  </script>  </head>  <body>   <div>    <h4>URL - ws://localhost:8080/websocket/echo</h4>    <input id="target" type="text" size="40" style="width: 350px" />   </div>   <div>    <button id="connect" onclick="connect();">Connect</button>    <button id="disconnect" disabled="disabled" onclick="disconnect();">Disconnect</button>   </div>   <div>    <textarea id="message" style="width: 350px">Here is a message!</textarea>   </div>   <div>    <button id="echo" onclick="echo();" disabled="disabled">Echo message</button>   </div>   <div id="echomsg">   </div>  </body>  </html>
三 :运行与测试


打包部署到tomcat之后,启动chrom浏览器,输入地址:

http://localhost:8080/websocket/echo.html 

后来,我还发现,tomcat实现websocket服务器端居然不支持子协议

跟3W上的测试URL结果不一样。

来自:http://blog.csdn.net/jia20003/article/details/48751847