Posted on 2009-11-19 18:28
疯狂 阅读(4019)
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java 、
dwr
效果：服务器端发出消息，各个客户端及时接受消息。
1，要使用dwr的ajaxReverse 技术首先要在web.xml里给dwr的servlet加上下列参数配置：
<param-name>activeReverseAjaxEnabled</param-name>
<param-value>true</param-value>
2，服务器端代码：
public class MyReverse {
public void sendMes(String mes){
send("系统消息："+mes);
}
public void send(final String output) {
String page = ServerContextFactory.get().getContextPath() + "/client.jsp";
Browser.withPage(page, new Runnable() {
public void run() {
Util.setValue("news", output); //news 客户端jsp里面textarea的id
}
});
}
}
3.dwr配置：
<create javascript="myrevsrse" creator="new">
<param name="class" value="com.dwr.MyReverse"/>
</create>
3.服务端 （server.jsp用于发消息也就是管理员界面）
<html>
<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/myrevsrse.js"></script>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
<script type="text/javascript">
function sendnews(){
var new_content = ${'newcontent'}.value;
myrevsrse.sendMes(new_content);
}
</script>
</head>
<body>
<input type="text" name="newcontent">
<input type = "button" value="发消息" onclick="sendnews()"/>
</body>
客户端：
<html>
<script type="text/javascript" src="dwr/engine.js"></script>
<script type="text/javascript" src="dwr/util.js"></script>
<head>
<<script type="text/javascript">
</script>
</head>
<body onload="dwr.engine.setActiveReverseAjax(true);">
<textarea rows="20" cols="20" id="news"></textarea>
</body>
</html>
测试：
我们打开一个服务端，2和客户端, 
服务端发出消息，点击发消息后，个客户端将同步显示服务端发出的消息。
通过源代码看看情况：（个人见解，希望大家指导和讨论）：
首先看看client端onload中执行的dwr方法：onload="dwr.engine.setActiveReverseAjax(true); 此方法鉴于源代码：
org.directwebremoting.ui.dwr.Engine,方法内容：
/** *//**
* Does DWR poll the server for updates? (Default: false)
* @param activeReverseAjax True/False to turn RA on/off
* @see <a href="http://getahead.org/dwr/browser/engine/options">Options documentation</a>
*/
public static void setActiveReverseAjax(boolean activeReverseAjax)
{
ScriptBuffer script = new ScriptBuffer();
script.appendScript("dwr.engine.setActiveReverseAjax(")
.appendData(activeReverseAjax)
.appendScript(");");
ScriptSessions.addScript(script);
}接着会调用：
Collection<ScriptSession> sessions = Browser.getTargetSessions();
for (ScriptSession scriptSession : sessions)
{
scriptSession.addScript(script);
}
其中Browser.getTargetSessions();是这样说的：
/** *//**
* This method discovers the sessions that are currently being targeted
* by browser updates.
* <p>
* It will generally only be useful to authors of reverse ajax UI proxy
* APIs. Using it directly may cause scaling problems
* @return The list of current browser windows.
*/
public static Collection<ScriptSession> getTargetSessions()
{
TaskDispatcher taskDispatcher = TaskDispatcherFactory.get();
Collection<ScriptSession> sessions = taskDispatcher.getTargetSessions();
if (sessions != null)
{
return sessions;
}
WebContext webContext = WebContextFactory.get();
if (webContext != null)
{
sessions = new ArrayList<ScriptSession>();
sessions.add(webContext.getScriptSession());
return sessions;
}
throw new IllegalStateException("No current UI to manipulate. See org.directwebremoting.Browser to set one.");
}
这个方法只对reverse代理有用，直接使用它可能会有问题，
这里将看到WebContent 这个是关键：这里记录了client端连接的信息，而最重要的当然是session和response，最终服务端信息是同过response的PrintWriter来输出到客户端，而实际上dwrServlet在处理requst的时候调用了这个类，调用内容看下代码：
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
{
try
{
webContextBuilder.engageThread(container, request, response);
UrlProcessor processor = container.getBean(UrlProcessor.class);
processor.handle(request, response);
}
finally
{
webContextBuilder.disengageThread();
}
}
其中的ebContextBuilder.engageThread(container, request, response);正式调用了这个类：
public void engageThread(Container container, HttpServletRequest request, HttpServletResponse response)
{
try
{
ServletConfig servletConfig = container.getBean(ServletConfig.class);
ServletContext servletContext = container.getBean(ServletContext.class);
WebContext ec = new DefaultWebContext(container, request, response, servletConfig, servletContext);
user.set(ec);
}
catch (Exception ex)
{
log.fatal("Failed to create an ExecutionContext", ex);
}
}
通过webcontext将我们的请求信息维持在服务端，
具体下面的过程的大意就是 通过过滤所有scriptsession 是否含有dwr.engine.setActiveReverseAjax(true); 信息 并通过response发出服务端信息。
时间关系欢迎大家继续讨论！