定时器

代码：

import java.text.SimpleDateFormat;
import java.util.Timer;
import java.util.TimerTask;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;


public class TimeJobDemo implements ServletContextListener{
	Timer timer;
	public void contextDestroyed(ServletContextEvent arg0) {
		timer.cancel();
		System.out.println("定时器关闭");
	}

	public void contextInitialized(ServletContextEvent arg0) {
		System.out.println("定时器启动");
		timer=new Timer();
		timer.schedule(new Task(),5000,20*1000);//服务启动5秒后，每隔二十秒执行一次
		System.out.println("----XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX");
	}

}

class Task extends TimerTask{
	private static SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
	@Override
	public void run() {
		System.out.println("开始执行任务:"+sdf.format(new java.util.Date()));
		try {
			Thread.sleep(5000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("执行任务。。。。。。。");
		System.out.println("执行任务结束:"+sdf.format(new java.util.Date()));
	}
	
}

web.xml->

  <listener>
    <listener-class>TimeJobDemo</listener-class>
  </listener>