WebSocket 实现之 Tomcat

搞定这个的过程远比想象的困难许多。网上许多教程，一一尝试，大多随着库版本的改变以及浏览器对协议支持的改变以失败告终，即使成功的也语焉不详，以下为步骤。

1. 运行环境

Java EE IDE

apache-tomcat-7.0.29(7.0.27之后才支持websocket)

IE(版本：10.0.9200.16384)

Firefox(版本：15.0)

Google Chrome(版本：23.0.1251.2)

2. 详细步骤

(1) 在Java EE IDE中，File->New->Dynamic Web Project，使其如下配置

Target runtime中必须是Apache Tomcat v7.0,并且最好是引用7.0.29(可在New Runtime中配置)

注意，点击Next->,再点击Next->,如下图，注意勾选Generate web.xml deployment descriptor，点击Finish

(2) 在Java Resources下src下New->Class,如下图

再在src下New->Class,如下图

下面贴上上述类的代码

package com.trump.web.servlet;

import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;

import javax.servlet.http.HttpServletRequest;

import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WebSocketServlet;

public class EchoServlet extends WebSocketServlet {
    private static final long serialVersionUID = -4104682919545889813L;

    private Logger logger = Logger.getLogger(EchoServlet.class.getName());

    private static List<MyMessageInbound> socketList = new ArrayList<MyMessageInbound>();

    @Override
    protected StreamInbound createWebSocketInbound(String subProtocol,
            HttpServletRequest request) {
        // TODO Auto-generated method stub
        logger.info("receive ws request");
        return new MyMessageInbound();
    }

    public static synchronized List<MyMessageInbound> getSocketList() {
        return socketList;
    }
}

package com.trump.web.servlet;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.util.logging.Logger;

import org.apache.catalina.websocket.MessageInbound;
import org.apache.catalina.websocket.WsOutbound;

public class MyMessageInbound extends MessageInbound {
    private int userIdName = 0;
    private Logger logger = Logger.getLogger(MyMessageInbound.class.getName());

    public int getUserIdName() {
        return userIdName;
    }

    protected void onOpen(WsOutbound outbound) {
        super.onOpen(outbound);
        userIdName = outbound.hashCode();
        EchoServlet.getSocketList().add(this);
        logger.info("Server onOpen");
    }

    protected void onClose(int status) {
        EchoServlet.getSocketList().remove(this);
        super.onClose(status);
        logger.info("Server onClose");
    }

    // 有二进制消息数据到达，比如音频等文件传输
    @Override
    protected void onBinaryMessage(ByteBuffer buffer) throws IOException {
        logger.info("Binary Message Receive: " + buffer.remaining());
    }

    @Override
    protected void onTextMessage(CharBuffer buffer) throws IOException {
        String msgOriginal = buffer.toString();

        int startIndex = msgOriginal.indexOf("!@#$%");
        String nikeName = msgOriginal.substring(0, startIndex);
        String textMsg = msgOriginal.substring(startIndex + 5);
        // 将字符数组包装到缓冲区中
        // 给定的字符数组将支持新缓冲区；即缓冲区修改将导致数组修改，反之亦然

        String countMsg = EchoServlet.getSocketList().size() + "人同时在线";
        logger.info("Server onTextMessage: " + countMsg + nikeName + ":"
                + textMsg);

        String msg1 = nikeName + ": " + textMsg;
        String msg2 = "我: " + textMsg;

        for (MyMessageInbound messageInbound : EchoServlet.getSocketList()) {
            CharBuffer msgBuffer1 = CharBuffer.wrap(msg1);
            CharBuffer msgBuffer2 = CharBuffer.wrap(msg2);

            WsOutbound outbound = messageInbound.getWsOutbound();
            if (messageInbound.getUserIdName() != this.getUserIdName()) {
                outbound.writeTextMessage(msgBuffer1);
                outbound.flush();
            } else {
                outbound.writeTextMessage(msgBuffer2);
            }
        }
    }
}

(3) 打开WebContent下WEB-INF下web.xml,编辑为

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">
    <display-name>myWebSocket</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
    </welcome-file-list>

    <servlet>
        <servlet-name>echo</servlet-name>
        <servlet-class>com.trump.web.servlet.EchoServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>echo</servlet-name>
        <url-pattern>*.ws</url-pattern>
    </servlet-mapping>
</web-app>

(4) 右击项目myWebSocket->Run As->Run on Server,如下图，点击Finish,

可以看到Tomacat正常运行，如下图

(5) 在任意位置新建一个客户端，命名为client.html,内容如下

<!DOCTYPE html>
<html>
<head>
<title>Web Socket Demo</title>
<script type="text/javascript">
    var ws = null;
    function startServer() {
        var url = "ws://127.0.0.1:8080/myWebSocket/echo.ws";
        if ('WebSocket' in window) {
            ws = new WebSocket(url);
        } else if ('MozWebSocket' in window) {
            ws = new MozWebSocket(url);
        } else {
            alert('Your browser Unsupported WebSocket!');
            return;
        }

        ws.onopen = function() {
            document.getElementById("content").innerHTML += 'websocket open! Welcome!<br />';
        };
        ws.onmessage = function(event) {
            document.getElementById("content").innerHTML += event.data + '<br />';
        };
        ws.onclose = function() {
            document.getElementById("content").innerHTML += 'websocket closed! Byebye!<br />';
        };
    }

    function sendMyMessage() {
        var nickName = document.getElementById('nickName');
        var textMessage = document.getElementById('textMessage');
        if (ws != null && textMessage.value != '') {
            ws.send(nickName.value + '!@#$%' + textMessage.value);
            textMessage.value = '';
        }
    }
</script>
</head>
<body onload="startServer()">
    昵称:
    <input type="text" id="nickName" size="20" />
    <br />
    <input type="text" id="textMessage" size="20" />
    <input type="button" onclick="sendMyMessage()" value="Send">
    <div id="content"></div>
</html>

(6) OK!打开浏览器，输入http://localhost:8080/webSocketTest/client.html

此时注意Tomcat打印出的信息，如下

3. WebSocket之所以受关注，是因为它的服务器端能主动发消息给客户端，即MyMessageInbound中onOpen函数可以让服务器做想做的事情。