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對于頁面一直監控,以前都是使用ajax請求即可,但是小并發這做法沒多大問題,但是到了大并發就不太合適,如果不想自己寫線程來操控就可以偷懶找一些插件,例如comet4j

下面我來演示下如何使用這個插件

先準備需要的工具:

comet4j-tomcat6.jar(tomcat6的就導入這個)

comet4j-tomcat7.jar(tomcat7的就導入這個)

comet4j.js(頁面引入這個js)

具體操作看下面

然后就寫個class

[java] view plain copy

package com.shadow.extras.comet4j;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import org.comet4j.core.CometContext;
import org.comet4j.core.CometEngine;
public class TestComet implements ServletContextListener {
private static final String CHANNEL = "test";
private static final String CHANNEL2 = "test2";
public void contextInitialized(ServletContextEvent arg0) {
CometContext cc = CometContext.getInstance();
cc.registChannel(CHANNEL);// 注冊應用的channel
cc.registChannel(CHANNEL2);
Thread helloAppModule = new Thread(new HelloAppModule(),
"Sender App Module");
// 是否啟動
helloAppModule.setDaemon(true);
// 啟動線程
helloAppModule.start();
Thread helloAppModule2 = new Thread(new HelloAppModule2(),
"Sender App Module");
// 是否啟動
helloAppModule2.setDaemon(true);
// 啟動線程
helloAppModule2.start();
}
class HelloAppModule2 implements Runnable {
public void run() {
while (true) {
try {
// 睡眠時間
Thread.sleep(5000);
} catch (Exception ex) {
ex.printStackTrace();
}
CometEngine engine = CometContext.getInstance().getEngine();
// 獲取消息內容
long l = getFreeMemory();
// 開始發送
engine.sendToAll(CHANNEL2, l);
}
}
}
class HelloAppModule implements Runnable {
public void run() {
while (true) {
try {
// 睡眠時間
Thread.sleep(2000);
} catch (Exception ex) {
ex.printStackTrace();
}
CometEngine engine = CometContext.getInstance().getEngine();
// 獲取消息內容
long l = getFreeMemory();
// 開始發送
engine.sendToAll(CHANNEL, l);
}
}
}
public void contextDestroyed(ServletContextEvent arg0) {
}
public long getFreeMemory() {
return Runtime.getRuntime().freeMemory() / 1024;
}
}

然后再寫個頁面

[html] view plain copy

<!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="plugin/comet4j/comet4j.js"></script>
<script type="text/javascript">
function init(){
var kbDom = document.getElementById('kb');
var kbDom2 = document.getElementById('kb2');
JS.Engine.on({
test : function(aa){//偵聽一個channel
kbDom.innerHTML = aa;
},
test2 : function(bb){
kbDom2.innerHTML = bb;
}
});
JS.Engine.start('comet');
}
</script>
</head>
<body onload="init()">
剩余內存：<span id="kb">...</span>KB <br/>
剩余內存：<span id="kb2">...</span>KB
</body>
</html>

接著配置下web.xml就ok了

[html] view plain copy

<listener>
<description>Comet4J容器偵聽</description>
<listener-class>org.comet4j.core.CometAppListener</listener-class>
</listener>
<servlet>
<description>Comet連接[默認:org.comet4j.core.CometServlet]</description>
<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>/comet</url-pattern>
</servlet-mapping>
<listener>
<description>TestComet</description>
<listener-class>com.shadow.extras.comet4j.TestComet</listener-class>
</listener>

最后修改下tomcat的server.xml文件

把protocol參數值改成下面的,因為這是基于nio開發的插件

[html] view plain copy

<Connector URIEncoding="UTF-8" connectionTimeout="20000" port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol" redirectPort="8443"/>

測試,很簡單就是訪問我們剛剛創建的test.html,然后就可以看到內存數值一直自動刷新波動

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