Java中用Servlet Listener实现定时监听 (Timer、TimerTask)

Java中用Servlet Listener实现定时监听 (Timer、TimerTask)

转载自: http://www.zjsyc.com/blog/article/J2EE/318.html

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 >

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