研究了一天半，终于模拟出了这个功能，网上DWR的资料不少，但是真正实现客户端向服务器端精确推送消息的只有两篇文章。但是代码都只有一部分，向我这种刚开始学习DWR的人来说要看懂真的蛮难。不过即便如此，http://www.blogjava.net/stevenjohn/archive/2012/07/07/382447.html这片文章还是给了我很大帮助，再次表示感谢，下面我将这两天的研究详细记录下来备忘，也希望能帮助到像我一样的人。只写过程，不写原理（不是不写，而是有些地方我也不太懂），下面开始：
第一、在项目中引入dwr.jar，然后在web.xml中进行配置，配置如下：
<servlet>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>
org.directwebremoting.servlet.DwrServlet
</servlet-class>
<init-param>
<param-name>crossDomainSessionSecurity</param-name>
<param-value>false</param-value>
</init-param>
<init-param>
<param-name>allowScriptTagRemoting</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>classes</param-name>
<param-value>java.lang.Object</param-value>
</init-param>
<init-param>
<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>3000</param-value>
</init-param>
<init-param>
<param-name>debug</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>logLevel</param-name>
<param-value>WARN</param-value>
</init-param>
</servlet>
第二：在web.xml的同级目录下新建dwr.xml文件，内容如下
<!DOCTYPE dwr PUBLIC
"-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN"
"http://getahead.org/dwr/dwr30.dtd">
<dwr>
<alow>
<create creator="new" javascript="MessagePush">
<param name="class" value="com.huatech.messageremind.service.MessagePush"/>
</create>
<create creator="new" javascript="TestPush">
<param name="class" value="com.huatech.messageremind.service.Test"/>
</create>
</alow>
</dwr>
这个是dwr的基本配置，MessagePush在页面的javascript中使用，这个是对被推送页面开放的java类，Test是对推送页面开放的java类。场景：管理员后台登陆，发布一条消息，通过Test推送到后台，后台通过MessagePush推送给指定的用户，当然，至于怎么找到指定的用户，下面会说。
第三，被推送的页面代码
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>DWR DEMO</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
</head>
<script type='text/javascript' src='dwr/engine.js'></script>
<script type='text/javascript' src='dwr/util.js'></script>
<script type="text/javascript" src="dwr/interface/MessagePush.js"></script>
<script type="text/javascript">
//通过该方法与后台交互，确保推送时能找到指定用户
function onPageLoad(){
var userId = '${userinfo.humanid}';
MessagePush.onPageLoad(userId);
}
//推送信息
function showMessage(autoMessage){
alert(autoMessage);
}
</script>
<body onload="onPageLoad();dwr.engine.setActiveReverseAjax(true);dwr.engine.setNotifyServerOnPageUnload(true);;">
This is my DWR DEOM page. <hr>
<br>
<div id="DemoDiv">demo</div>
</body>
</html>
以上代码的简单解释：
页面页面onload的3个函数都是必须的，后两个是dwr的，第一个是将登录用户的userid与对应 的scriptSession进行处理，以便精确推送的时候能找到推送对象
第四 MessagePush类中实现的方法如下：
public void onPageLoad(String userId) {
ScriptSession scriptSession = WebContextFactory.get().getScriptSession();
scriptSession.setAttribute(userId, userId);
DwrScriptSessionManagerUtil dwrScriptSessionManagerUtil = new DwrScriptSessionManagerUtil();
try {
dwrScriptSessionManagerUtil.init();
System.out.println("cacaca");
} catch (ServletException e) {
e.printStackTrace();
}
}
里面对应的DwrScriptSessionManagerUtil 对应如下：
import javax.servlet.ServletException;
import javax.servlet.http.HttpSession;
import org.directwebremoting.Container;
import org.directwebremoting.ServerContextFactory;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.event.ScriptSessionEvent;
import org.directwebremoting.event.ScriptSessionListener;
import org.directwebremoting.extend.ScriptSessionManager;
import org.directwebremoting.servlet.DwrServlet;
public class DwrScriptSessionManagerUtil extends DwrServlet{
private static final long serialVersionUID = -7504612622407420071L;
public void init()throws ServletException {
Container container = ServerContextFactory.get().getContainer();
ScriptSessionManager manager = container.getBean(ScriptSessionManager.class);
ScriptSessionListener listener = new ScriptSessionListener() {
public void sessionCreated(ScriptSessionEvent ev) {
HttpSession session = WebContextFactory.get().getSession();
String userId =((User) session.getAttribute("userinfo")).getHumanid()+"";
System.out.println("a ScriptSession is created!");
ev.getSession().setAttribute("userId", userId);
}
public void sessionDestroyed(ScriptSessionEvent ev) {
System.out.println("a ScriptSession is distroyed");
}
};
manager.addScriptSessionListener(listener);
}
}
第五 推送页面代码：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'MyJsp.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<script type="text/javascript" src="<%=request.getContextPath() %>/js/jquery-1.5.1.js"></script>
<script type='text/javascript' src='dwr/engine.js'></script>
<script type='text/javascript' src='dwr/util.js'></script>
<script type='text/javascript' src='dwr/interface/TestPush.js'></script>
<script type="text/javascript">
function test() {
var msg = document.getElementById("msgId").value;
//msg = {msgId: '1', context: $("#msgContext").val()};
TestPush.sendMessageAuto(msg,"哈哈哈");
}
</script>
</head>
<body>
id : <input type="text" name="msgId" id="msgId" /> <br />
<input type="button" value="Send" onclick="test()" />
</body>
</html>
第六：精确推送要实现的代码：
public class Test{
public void sendMessageAuto(String userid, String message){
final String userId = userid;
final String autoMessage = message;
Browser.withAllSessionsFiltered(new ScriptSessionFilter() {
public boolean match(ScriptSession session){
if (session.getAttribute("userId") == null)
return false;
else
return (session.getAttribute("userId")).equals(userId);
}
}, new Runnable(){
private ScriptBuffer script = new ScriptBuffer();
public void run(){
script.appendCall("showMessage", autoMessage);
Collection<ScriptSession> sessions = Browser
.getTargetSessions();
for (ScriptSession scriptSession : sessions){
scriptSession.addScript(script);
}
}
});
}
}
至此 这个例子的代码都已经贴出来了，应该是可以跑通的，有问题的话可以给我留言。当然，要自己写个登录，然后把userId放到session里面，这个比较简单，就不贴代码了，有问题可以在http://download.csdn.net/detail/luojia_wang/5275588上下载原项目。我只是简单的做了一个能实现功能的例子，还有很多地方要研究，比如跟spring整合，还可能有很多优化，等我继续学习一下再说.