Java并发编程：ScheduledExecutorService执行周期任务

淩亂°似流年 2022-06-07 04:25 191阅读 0赞

该接口在java.util.concurrent包下，具体可参见[API][]  
项目中用到了cheduledExecutorService中的scheduleWithFixedDelay方法，就顺便把其中几个关重要的方法学习下：

## 1.schedule ##

schedule(Runnable command, long delay, TimeUnit unit)，schedule方法被用来延迟指定时间后执行某个指定任务。  
command：定时任务  
delay：延迟时间  
unit：时间单位  
a.代码如下：

import java.text.SimpleDateFormat;
    import java.util.Date;
    
    /** * @author someone * @create 2017-10-10 19:01 **/
    public class Job implements Runnable { 
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
    
        public void run() {
            try {
                Thread.sleep(5000);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
            System.out.println("do something at:" + sdf.format(new Date()));
        }
    }
    
    
    import java.text.SimpleDateFormat;
    import java.util.Date;
    import java.util.concurrent.Executors;
    import java.util.concurrent.ScheduledExecutorService;
    import java.util.concurrent.TimeUnit;
    
    /** * @author someone * @create 2017-10-10 19:01 **/
    public class ScheduledExecutorServiceTest { 
        //测试
        public static void main(String[] args) {
            ScheduledExecutorService schedule = Executors.newScheduledThreadPool(5);
            final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
            System.out.println(" begin to do something at:" + sdf.format(new Date()));
            schedule.schedule(new Job(),1, TimeUnit.SECONDS);
        }
    }

b.输出如下：

begin to do something at:2017-10-10 07:02:31
    do something  at:2017-10-10 07:02:37

## 2.scheduleWithFixedDelay ##

scheduleWithFixedDelay(Runnable command, long initialDelay, long delay,TimeUnit unit)  
创建并执行一个在给定初始延迟后首次启用的定期操作，随后，在每一次执行终止和下一次执行开始之间都存在给定的延迟，如果任务的执行时间超过了廷迟时间（delay），下一个任务则会在  
（当前任务执行所需时间+delay）后执行。  
command：定时任务  
initialDelay：初始延迟时间  
delay：指定延迟时间  
unit：时间单位

a.代码如下：

import java.text.SimpleDateFormat;
    import java.util.Date;
    import java.util.concurrent.Executors;
    import java.util.concurrent.ScheduledExecutorService;
    import java.util.concurrent.TimeUnit;
    
    /** * @author someone * @create 2017-10-10 19:01 **/
    public class ScheduledExecutorServiceTest { 
    
        public static void main(String[] args) {
            ScheduledExecutorService schedule = Executors.newScheduledThreadPool(5);
            final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
            System.out.println(" begin to do something at:" + sdf.format(new Date()));
            //schedule.schedule(new Job(),1, TimeUnit.SECONDS);
            schedule.scheduleWithFixedDelay(new Job(), 1, 2, TimeUnit.SECONDS);
        }
    }

b.输出如下：

begin to do something at:2017-10-10 07:06:51
    do something  at:2017-10-10 07:06:57
    do something  at:2017-10-10 07:07:04
    do something  at:2017-10-10 07:07:11
    do something  at:2017-10-10 07:07:18
    do something  at:2017-10-10 07:07:25

第一次延时5+1s  
以后每次延时5+2s

## 3.scheduleAtFixedRate ##

scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)  
创建并执行一个在给定初始延迟后首次启用的定期操作，后续操作具有给定的周期；也就是将在 initialDelay 后开始执行，然后在initialDelay+period 后执行，接着在 initialDelay + 2 \* period 后执行，依此类推。如果任务的执行时间小于period，将会按上述规律执行。否则，则会按 任务的实际执行时间进行周期执行。  
initialDelay:初始延时时间  
period：延时周期  
unit：时间单位  
a.代码如下：

import java.text.SimpleDateFormat;
    import java.util.Date;
    import java.util.concurrent.Executors;
    import java.util.concurrent.ScheduledExecutorService;
    import java.util.concurrent.TimeUnit;
    
    /** * @author someone * @create 2017-10-10 19:01 **/
    public class ScheduledExecutorServiceTest { 
    
        public static void main(String[] args) {
            ScheduledExecutorService schedule = Executors.newScheduledThreadPool(5);
            final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
            System.out.println(" begin to do something at:" + sdf.format(new Date()));
            //schedule.schedule(new Job(),1, TimeUnit.SECONDS);
            //schedule.scheduleWithFixedDelay(new Job(), 1, 2, TimeUnit.SECONDS);
            schedule.scheduleAtFixedRate(new Job(), 1,2, TimeUnit.SECONDS);
        }
    }

b.结果输出：

begin to do something at:2017-10-10 07:13:57
    do something  at:2017-10-10 07:14:03
    do something  at:2017-10-10 07:14:08
    do something  at:2017-10-10 07:14:13
    do something  at:2017-10-10 07:14:18
    do something  at:2017-10-10 07:14:23

初始时间延时：5+1s  
以后每次延时为1+2\*2s

参考：[http://kim-miao.iteye.com/blog/1618713][http_kim-miao.iteye.com_blog_1618713]

[API]: http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledExecutorService.html
[http_kim-miao.iteye.com_blog_1618713]: http://kim-miao.iteye.com/blog/1618713