错误的写法

如果按照下图的写法，两个任务不会同时执行，因为是一个线程，两个任务是串行的关系。

可以看到第二个任务是等第一个任务执行完以后，才执行的。

正确的写法

使用线程池，为每一个任务创建一个线程
可以看到两个任务同时执行了，一个任务设定的是1秒后执行，另一个任务设定的是3秒后执行，两个任务同时执行了。

代码

package com.yyy.servlet;

import java.io.IOException;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class TestScheduledExecutorService
 */
@WebServlet("/TestScheduledExecutorService")
public class TestScheduledExecutorService extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
	private static long start;
    /**
     * @see HttpServlet#HttpServlet()
     */
    public TestScheduledExecutorService() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		//response.getWriter().append("Served at: ").append(request.getContextPath());
		
		start=System.currentTimeMillis();
		//timer比较适用于单个任务
		
		/*Timer timer=new Timer();
		
		
		
		timer.schedule(new TimerTask() {
			
			@Override
			public void run() {
				// TODO Auto-generated method stub
				System.out.println("执行时间距离开始时间为:"+(System.currentTimeMillis()-start));
			
				try {
					Thread.sleep(6000);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}			
			}
		}, 1000);
	
		timer.schedule(new TimerTask() {
			
			@Override
			public void run() {
				// TODO Auto-generated method stub
				System.out.println("执行时间距离开始时间为:"+(System.currentTimeMillis()-start));
				
			}
		}, 3000);*/
		
		
		//要执行多个任务要改成任务调度的线程池
		ScheduledExecutorService scheduledExecutorService=   Executors.newScheduledThreadPool(2);
		
		scheduledExecutorService.schedule(new TimerTask() {
			
			@Override
			public void run() {
				// TODO Auto-generated method stub
				System.out.println("执行时间距离开始时间为:"+(System.currentTimeMillis()-start));
			
				try {
					Thread.sleep(6000);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
		}}, 1000,TimeUnit.MILLISECONDS );
		
         scheduledExecutorService.schedule(new TimerTask() {
			
			@Override
			public void run() {
				// TODO Auto-generated method stub
				System.out.println("执行时间距离开始时间为:"+(System.currentTimeMillis()-start));
				
		}}, 3000,TimeUnit.MILLISECONDS );
		
	
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}