DWR Server Push(服务器推技术) 实现即时聊天功能(WEB)

原文 http://yourgame.iteye.com/blog/199079

当你有QQ消息时,QQ的小图标会晃动,我们甚至还可以设定QQ有消息时,自动弹出来!
这些在C/S模式下很容易实现!如果要在B/S模式如何来实现呢?
我们的肯定会想到在客服端调用ajax在后台不断的查询服务器.看是否有关于自己的消息.如果有则查询返回.这种做法肯定会大量的占用系统的资源!不可取!
现在DWR的反转AJAX功能.允许我们从服务器端来控制客服端.而不需要客户端来请求.服务器可以自动把消息发给指定的客户端!

已经实现了对指定用户发送消息的功能,并且即时显示在指定的用户界面上面.当然你可以修改这些,让它弹出来显示,或者像QQ一样在你页面的某个角落让消息的图标闪动:)
下面我做一个简单的说明:

package com.lhq;  
  
/** 
 * 用户类 
 *  
 * @author 廖瀚卿 
 *  
 */  
public class User {  
  
    private String userid;  
  
    private String username;  
  
    public String getUserid() {  
        return userid;  
    }  
  
    public void setUserid(String userid) {  
        this.userid = userid;  
    }  
  
    public String getUsername() {  
        return username;  
    }  
  
    public void setUsername(String username) {  
        this.username = username;  
    }  
  
    public User(String userid, String username) {  
        super();  
        this.userid = userid;  
        this.username = username;  
    }  
  
}

<%@ page language="java" pageEncoding="GBK"%>  
<html>  
    <head>  
        <title>chat</title>  
        <meta http-equiv="pragma" content="no-cache">  
        <meta http-equiv="cache-control" content="no-cache">  
        <meta http-equiv="expires" content="0">  
        <script type='text/javascript' src='/chat/dwr/interface/ChatManager.js'></script>  
        <script type='text/javascript' src='/chat/dwr/engine.js'></script>  
        <script type='text/javascript' src='/chat/dwr/util.js'></script>  
        <script type="text/javascript" src="https://my.oschina.net/chat/chat.js"></script>  
    </head>  
    <body>  
        <input type="hidden" name="userid" />  
        <br>  
        昵称:  
        <input type="text" name="username" />  
        <input type="button" value="注册" onclick="register(this);" />  
        <br />  
        <br />  
        我要对  
        <select name="receiver" id="receiver" disabled=true" >  
        </select>  
        说:  
        <input type="text" name="message" id="message" disabled="true" />  
        <input type="button" value="发送" id="send" name="send" disabled="true"  
            onclick="send();" />  
        <br />  
        <br />  
        在线用户列表:  
        <ul id="users">  
        </ul>  
  
        <div id="showMessage" style="display: none">  
            <span id="sender"></span>对你说:  
            <span id="msg"></span>  
        </div>  
    </body>  
</html>

package com.lhq;  
  
import java.util.ArrayList;  
import java.util.Collection;  
import java.util.HashSet;  
import java.util.List;  
  
import javax.servlet.ServletContext;  
import javax.servlet.http.HttpServletRequest;  
  
import org.directwebremoting.ScriptSession;  
import org.directwebremoting.ServerContext;  
import org.directwebremoting.ServerContextFactory;  
import org.directwebremoting.WebContextFactory;  
import org.directwebremoting.proxy.dwr.Util;  
  
/** 
 * 处理聊天相关 
 *  
 * @author 廖瀚卿 
 *  
 */  
public class ChatManager {  
  
    /** 保存当前在线用户列表 */  
    public static List<User> users = new ArrayList<User>();  
  
    /** 
     * 更新在线用户列表 
     * @param username 待添加到列表的用户名 
     * @param flag 是添加用户到列表,还是只获得当前列表 
     * @param request 
     * @return 用户userid 
     */  
    public String updateUsersList(String username, boolean flag, HttpServletRequest request) {  
        User user = null;  
        if (flag) {   
            // 这里取会话(HttpSession)的id为用户id   
            user = new User(request.getSession().getId(), username);  
            //保存用户到列表  
            users.add(user);      
            //将用户id和页面脚本session绑定  
            this.setScriptSessionFlag(user.getUserid());  
        }  
        //获得DWR上下文  
        ServletContext sc = request.getSession().getServletContext();  
        ServerContext sctx = ServerContextFactory.get(sc);  
        //获得当前浏览 index.jsp 页面的所有脚本session  
        Collection sessions = sctx.getScriptSessionsByPage("/chat/index.jsp");  
        Util util = new Util(sessions);  
        //处理这些页面中的一些元素  
        util.removeAllOptions("users");  
        util.addOptions("users", users, "username");  
        util.removeAllOptions("receiver");  
        util.addOptions("receiver", users,"userid","username");  
        if(!flag){  
            return null;  
        }  
        return user.getUserid();  
    }  
  
    /** 
     * 将用户id和页面脚本session绑定 
     * @param userid 
     */  
    public void setScriptSessionFlag(String userid) {  
        WebContextFactory.get().getScriptSession().setAttribute("userid", userid);  
    }  
  
    /** 
     * 根据用户id获得指定用户的页面脚本session 
     * @param userid 
     * @param request 
     * @return 
     */  
    @SuppressWarnings("unchecked")  
    public ScriptSession getScriptSession(String userid, HttpServletRequest request) {  
        ScriptSession scriptSessions = null;  
        Collection<ScriptSession> sessions = new HashSet<ScriptSession>();  
        sessions.addAll(ServerContextFactory.get(request.getSession().getServletContext())  
                .getScriptSessionsByPage("/chat/index.jsp"));  
        for (ScriptSession session : sessions) {  
            String xuserid = (String) session.getAttribute("userid");  
            if (xuserid != null && xuserid.equals(userid)) {  
                scriptSessions = session;  
            }  
        }  
        return scriptSessions;  
    }  
      
    /** 
     * 发送消息 
     * @param sender 发送者 
     * @param receiverid 接收者id 
     * @param msg 消息内容 
     * @param request 
     */  
    public void send(String sender,String receiverid,String msg,HttpServletRequest request){  
        ScriptSession session = this.getScriptSession(receiverid, request);  
        Util util = new Util(session);  
        util.setStyle("showMessage", "display", "");  
        util.setValue("sender", sender);  
        util.setValue("msg", msg);  
    }  
}

/** 
 * 注册帐号 
 */  
function register(button) {  
    if ($('username').value == "" || $('username').value.length <= 0) {  
        alert("请输入昵称");  
        return;  
    }  
  
    /* 下面是对一些按钮的禁用和激活操作 */  
    $('username').disabled = true;  
    button.disabled = true;  
    $('message').disabled = false;  
    $('send').disabled = false;  
    $('receiver').disabled = false;  
  
    /* 把我输入的用户名注册到服务器,并获得用户id(这里用session id 代替) */  
    ChatManager.updateUsersList($('username').value, true, function(data) {  
        if (data != null && data.length > 0) {  
            $('userid').value = data; // 注册成功,把userid放到当前页面  
        }  
    });  
}  
  
/** 
 * 页面初始化 
 */  
function init() {  
    dwr.engine.setActiveReverseAjax(true); // 激活反转 重要  
    ChatManager.updateUsersList(null, false); // 当你打开界面的时候,先获得在线用户列表.  
}  
  
/** 
 * 发送消息 
 */  
function send() {  
    var sender = dwr.util.getValue('username'); // 获得发送者名字  
    var receiver = dwr.util.getValue('receiver'); // 获得接受者id  
    var msg = dwr.util.getValue('message'); // 获得消息内容  
    ChatManager.send(sender, receiver, msg); // 发送消息  
}  
  
window.onload = init;//页面加载完毕后执行初始化方法init

<?xml version="1.0" encoding="UTF-8"?>  
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee   
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">  
    <welcome-file-list>  
        <welcome-file>index.jsp</welcome-file>  
    </welcome-file-list>  
    <servlet>  
        <servlet-name>dwr-invoker</servlet-name>  
        <servlet-class>  
            org.directwebremoting.servlet.DwrServlet  
        </servlet-class>  
        <init-param>  
            <description>调试DWR,发布系统时应将其设为false</description>  
            <param-name>debug</param-name>  
            <param-value>true</param-value>  
        </init-param>  
        <init-param>  
            <description>使用服务器推技术(反转AJAX)</description>  
            <param-name>activeReverseAjaxEnabled</param-name>  
            <param-value>true</param-value>  
        </init-param>  
        <init-param>  
            <param-name>  
                initApplicationScopeCreatorsAtStartup  
            </param-name>  
            <param-value>true</param-value>  
        </init-param>  
        <init-param>  
            <param-name>maxWaitAfterWrite</param-name>  
            <param-value>100</param-value>  
        </init-param>  
        <load-on-startup>4</load-on-startup>  
    </servlet>  
    <servlet-mapping>  
        <servlet-name>dwr-invoker</servlet-name>  
        <url-pattern>/dwr/*</url-pattern>  
    </servlet-mapping>  
</web-app>

<?xml version="1.0" encoding="UTF-8"?>  
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://getahead.org/dwr/dwr20.dtd">  
<dwr>  
    <allow>  
        <convert converter="bean" match="com.lhq.User"/>  
        <create creator="new" javascript="ChatManager">  
             <param name="class" value="com.lhq.ChatManager"/>  
        </create>  
    </allow>  
</dwr>

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