研究了一天半，終於模擬出了這個功能，網上DWR的資料不少，但是真正實現客戶端向服務器端精確推送消息的只有兩篇文章。但是代碼都只有一部分，向我這種剛開始學習DWR的人來說要看懂真的蠻難。不過即便如此，http://www.blogjava.net/stevenjohn/archive/2012/07/07/382447.html這片文章還是給了我很大幫助，再次表示感謝，下面我將這兩天的研究詳細記錄下來備忘，也希望能幫助到像我一樣的人。只寫過程，不寫原理（不是不寫，而是有些地方我也不太懂），下面開始：
第一、在項目中引入dwr.jar，然後在web.xml中進行配置，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>
<servlet>
第二：在web.xml的同級目錄下新建dwr.xml文件，內容如下
<!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> 這個是dwr的基本配置，MessagePush在頁面的JavaScript中使用，這個是對被推送頁面開放的Java類，Test是對推送頁面開放的java類。場景：管理員後臺登陸，發佈一條消息，通過Test推送到後臺，後臺通過MessagePush推送給指定的用戶，當然，至於怎麼找到指定的用戶，下面會說。
第三，被推送的頁面代碼
<%@ 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">
//通過該方法與後臺交互，確保推送時能找到指定用戶
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>
以上代碼的簡單解釋：
頁面頁面onload的3個函數都是必須的，後兩個是dwr的，第一個是將登錄用戶的userid與對應 的scriptSession進行處理，以便精確推送的時候能找到推送對象
第四 MessagePush類中實現的方法如下：
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();
}
} 裏面對應的DwrScriptSessionManagerUtil 對應如下：
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 推送頁面代碼：
<%@ 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：精確推送要實現的代碼：
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 這個例子的代碼都已經貼出來了，應該是可以跑通的，有問題的話可以給我留言。當然，要自己寫個登錄，然後把userId放到session裏面，這個比較簡單，就不貼代碼了，有問題可以在http://download.csdn.net/detail/luojia_wang/5275588上下載原項目。我只是簡單的做了一個能實現功能的例子，還有很多地方要研究，比如跟spring整合，還可能有很多優化，等我繼續學習一下再說.