Java中用Servlet容器实现程序监听

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>