java服务器推的实现 -

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java服务器推的实现

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java服务器推

dwr

转载自：http://vincent-yy.iteye.com/blog/427922

小型聊天室--DWR实现服务器推技术

      当看到DWR2也可以实现推技术之后，想尝试一下！
首先当官方上下载一个dwr的jar文件和commons-logging-1.1.1.jar
先从配置文件入手
web.xml
Xml代码
<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" 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">

    
    <display-name>ajaxDWR</display-name>
    <servlet>
        <servlet-name>dwr-invoker</servlet-name>
        
        <servlet-class>
            org.directwebremoting.servlet.DwrServlet
        </servlet-class>
        <init-param>
            <description>实现调试，在debug请设置为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>
dwr.xml
Xml代码
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://www.getahead.ltd.uk/dwr/dwr20.dtd">
<dwr>
    
    <allow>
        <create creator="new" javascript="Chat">
            <param name="class" value="com.dwr.chat.Chat" />
        </create>
    </allow>
</dwr>

编写好配置文件之后，开始编写页面，我们可以选择html或者jsp都可以
index3.html
Html代码
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
    <head>
        <title>index3.html</title>

        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
        <meta http-equiv="description" content="this is my page">
        <meta http-equiv="content-type" content="text/html; charset=UTF-8">
        <script type='text/javascript' src='dwr/util.js'></script>
        <script type='text/javascript' src='dwr/engine.js'></script>
        <script type='text/javascript' src='dwr/interface/Chat.js'></script>
        

    </head>

    <body>
        <center>
            <table width="600px" border="1">
                <tr>
                    <td colspan="3" align="center">
                        XXXXXX Chat
                    </td>
                    <td>
                        User List
                    </td>
                </tr>
                <tr>
                    <td colspan="3" style="height: 300px">
                        <textarea rows="20" cols="60" readonly id="showmessage" name="showmessage"></textarea>
                    </td>
                    <td style="height: 300px" valign="top">
                        <div id="userlist" style="height:310px;overflow : scroll;"></div>
                    </td>
                </tr>
                <tr>
                    <td colspan="3" align="center">
                        <span id="say_name" ></span>
                        <textarea rows="3" cols="50" id="say_message" name="say_message"></textarea><input type="button" value="say" id="say" onclick="sayMessage()"/>
                    </td>
                    <td>
                        先录入你的昵称<br/>
                        <input type="text" style="width: 125px" name="name" id="name" />
                        <input type="button" value="确定" onclick="register()" />
                    </td>
                </tr>
            </table>
        </center>
    </body>
    <script type="text/javascript">
        dwr.engine.setActiveReverseAjax(true); // 激活反转重要

        init();

        function init(){
            document.getElementById('say_message').disabled = true;
            document.getElementById('say').disabled = true;
        }

        function sayMessage(){
            var message_content = DWRUtil.getValue('say_message');
            var message_head = document.getElementById('say_name').innerHTML;
            Chat.sayMessage(message_head+message_content);
            document.getElementById('say_message').value = '';
        }

        function register() {
            var name = DWRUtil.getValue("name");
            Chat.addUser(name,callback);
        }

        function callback(str) {
            if(str != ''){
                alert(str);
            }else{
                document.getElementById('say_name').innerHTML = DWRUtil.getValue("name") + " 说：";
                document.getElementById('say_message').disabled = false;
                document.getElementById('say').disabled = false;
            }
        }
    </script>
</html>
这个页面比较简陋，建议js写在下方，否则firefox会报错

Chat.java
Java代码
package com.dwr.chat;

import java.util.ArrayList;
import java.util.Collection;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;

import org.directwebremoting.ServerContext;
import org.directwebremoting.ServerContextFactory;
import org.directwebremoting.proxy.dwr.Util;

public class Chat {
    static ArrayList<String> name_list = new ArrayList<String>();
    static StringBuffer show_message = new StringBuffer();

    public String addUser(String name,HttpServletRequest request) {
        System.out.println("list.size() = "+name_list.size());
        for (String s : name_list) {
            if (name == null || name.trim().equals(s)) {
                return "用户名已存在";
            }
        }
        name_list.add(name.trim());
        ServletContext sc = request.getSession().getServletContext();
        ServerContext sctx = ServerContextFactory.get(sc);
        Collection sessions = sctx.getScriptSessionsByPage("/dwr2Demo/index3.html");
        Util util = new Util(sessions);
        show_message.append("\n欢迎"+name+"来到 XXX Chat");
        trimMessage();
        util.setValue("showmessage", show_message.toString());
        printUserList(util);
        return "";
    }

    public void sayMessage(String message,HttpServletRequest request){
        ServletContext sc = request.getSession().getServletContext();
        ServerContext sctx = ServerContextFactory.get(sc);
        Collection sessions = sctx.getScriptSessionsByPage("/dwr2Demo/index3.html");
        Util util = new Util(sessions);
        show_message.append("\n"+message);
        trimMessage();
        util.setValue("showmessage", show_message.toString());
        printUserList(util);
    }

    public void trimMessage(){
        if(show_message.length() > 2000){
            show_message.delete(0, ((show_message.length() - 2000)*2+2));
        }
    }

    public void printUserList(Util util){
        StringBuffer userlist = new StringBuffer();
        userlist.append("<table>");
        for(String s : name_list){
            userlist.append("<tr><td><font color='blue'>"+s+"</font></td></tr>");
        }
        userlist.append("</table>");
        util.setValue("userlist", userlist.toString());
    }
}

编写好这个之后，可以运行一下。
        经过测试，发现几个问题浏览器我现在测试了三种发现三种都有自己的特性
        IE                 ：比较正常，有时候会慢一些
        firefox          ：每次刷新访问的时候服务器会出现一个异常
        google浏览器：在刷新的时候会无限等待，一直到接收到信息

另一教程：http://hintcnuie.iteye.com/blog/175828

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