Java中用Servlet容器实现程序监听
类别: JAVA教程 
分两步走：（1）. 实现 javax.servlet.ServletContextListener 接口的两个方法：contextInitialized()和contextDestroyed() contextInitialized()：当Servlet容器启动时会执行 contextDestroyed()：当Servlet容器停止时会执行（2）. 在contextInitialized()中加入需要监听的程序，并由 java.util.Timer 的 schedule() 方法来控制监听程序执行的频率
DEMO（这是我的一个短信回复监听的程序原型，精简了一下）
----------------------------------------------------------------ReplyListener.java----------------------------------------------------------------
package com.hanweb.jcms;
import javax.servlet.*;
public class ReplyListener implements ServletContextListener { private ReplyTimer rt = null; public void contextInitialized(ServletContextEvent event) { String status = "[SYS] SMS reply listener start ."; event.getServletContext().log(status); System.out.println(status);
rt = new ReplyTimer(1); rt.start(); }
public void contextDestroyed(ServletContextEvent event) { String status = "[SYS] SMS reply listener stop ."; event.getServletContext().log(status); System.out.println(status);
if (rt != null) { rt.stop(); } }}
----------------------------------------------------------------ReplyTimer.java----------------------------------------------------------------
package com.hanweb.jcms;
import java.util.*;
public class ReplyTimer { private final Timer timer = new Timer(); private final int min;
public ReplyTimer(int minutes) { min = minutes; }
public void start() { Date date = new Date(); timer.schedule(new ReplyTask(), date, min * 60 * 1000); }
public void stop() { timer.cancel(); }}
----------------------------------------------------------------ReplyTask.java----------------------------------------------------------------
package com.hanweb.jcms;
import java.util.*;
public class ReplyTask extends TimerTask { public void doSomething() { System.out.println("[SYS] SMS reply listener running "); }
public void run() { doSomething(); }}
将编译好的class文件放入WEB-INF/classes中，最后别忘记了在Servlet容器中当前WEB应用的web.xml中加入监听语句：
<listener> <listener-class>com.hanweb.jcms.ReplyListener</listener-class> </listener>
