Java--Comet之服务端消息推送
Comet是一种用于web的推送技术，能使服务器能实时地将更新的信息传送到客户端，而无须客户端发出请求，目前有两种实现方式，长轮询和iframe流
一：所需资源
1.comet4j-tomcat7-v0.0.2.jar
2.servlet-api.jar 3.0
二：tomcat 配置（server.xml中启动nio）
<Connector protocol="org.apache.coyote.http11.Http11NioProtocol" connectionTimeout="20000" port="80" redirectPort="8443"/>
三：监听器配置(web.xml)
<listener>
<listener-class>org.comet4j.core.CometAppListener</listener-class>
</listener>
<servlet>
<display-name>CometServlet</display-name>
<servlet-name>CometServlet</servlet-name>
<servlet-class>org.comet4j.core.CometServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CometServlet</servlet-name>
<url-pattern>/conn</url-pattern>
</servlet-mapping>
<listener>
<description>HelloWorld</description>
<listener-class>org.comet4j.demo.helloworld.HelloWorld</listener-class>
</listener>
四：服务端代码示例
public class HelloWorld implements ServletContextListener {
private static final String CHANNEL = "hello";
public void contextInitialized(ServletContextEvent arg0) {
CometContext cc = CometContext.getInstance();
cc.registChannel(CHANNEL);//注册应用的channel
Thread helloAppModule = new Thread(new HelloAppModule(), "Sender App Module");
helloAppModule.setDaemon(true);
helloAppModule.start();
}
class HelloAppModule implements Runnable {
public void run() {
while (true) {
try {
Thread.sleep(1000);
} catch (Exception ex) {
ex.printStackTrace();
}
CometEngine engine = CometContext.getInstance().getEngine();
engine.sendToAll(CHANNEL, Runtime.getRuntime().freeMemory()/1024);
}
}
}
public void contextDestroyed(ServletContextEvent arg0) {
}
}
五：客户端代码示例
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta. http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Comet4J Hello World</title>
<script. type="text/javascript" src="js/comet4j.js"></script>
<script. type="text/javascript">
function init(){
alert(1);
var kbDom = document.getElementById('kb');
JS.Engine.on({
hello : function(kb){//侦听一个channel
kbDom.innerHTML = kb;
}
});
JS.Engine.start('conn');
JS.Engine.on(
'start',function(cId,channelList,engine){
alert('连接已建立，连接ID为：' + cId);
});
}
</script>
</head>
<body nload="init()">
剩余内存：<span id="kb">...</span>KB
</body>
</html>
六：开源的Comet框架
1.jetty
2.pushlet
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