使用ScheduledExecutorService实现Timer

大家都说Timer不太好用，经常会遇到：如果前边的一个任务比较慢，超出了period,此时timer的下一次轮询也会延迟。

同事说ScheduleExecutorService可以避免该问题，我写个例子测试下：

package com.dx.testparallel;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;;

public class TestTimer {
    public static void main(String[] args){
        ScheduledExecutorService scheduledExecutorService=Executors.newScheduledThreadPool();
        //Creates and executes a periodic action that becomes enabled
        //first after the given initial delay, and subsequently with the
        //given period; that is executions will commence after
        //initialDelay then initialDelay+period, then initialDelay + 2 *
        //period, and so on. If any execution of the task encounters an
        //exception, subsequent executions are suppressed.
        //Otherwise, the task will only terminate via cancellation or
        //termination of the executor. If any execution of this task
        //takes longer than its period, then subsequent executions may
        //start late, but will not concurrently execute.
        scheduledExecutorService.scheduleAtFixedRate(new TheTask(), ,, TimeUnit.MILLISECONDS);
    }
}

package com.dx.testparallel;

import java.sql.Timestamp;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.UUID;

import javax.lang.model.element.VariableElement;

public class TheTask implements Runnable{
    @Override
    public void run() {
          Timestamp ts = new Timestamp(System.currentTimeMillis());
          UUID uuid = UUID.randomUUID();
          System.out.println("task"+uuid+" start:"+ts.toString());

//          long num=0;
//          for(int a=0;a<100000;a++){
//              for(int i=0;i<1000000;i++){
//                  for(int j=0;j<1000000;j++){
//                      num= a*i*j;
//                  }
//              }
//          }
          try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

          ts = new Timestamp(System.currentTimeMillis());
          System.out.println("task"+uuid+" end:"+ts.toString());
    }
}

测试结果：为什么每次间隔时间是2s，而不是1s.

task418d088e-3288-4736-b40a-f3c4f496e2a2 start:2016-09-07 00:49:03.699
task418d088e-3288-4736-b40a-f3c4f496e2a2 end:2016-09-07 00:49:05.836
task741d2176-dbef-4f12-a73e-13a04ed5eb18 start:2016-09-07 00:49:05.836
task741d2176-dbef-4f12-a73e-13a04ed5eb18 end:2016-09-07 00:49:07.836
task96ebb6ca-c99b-482e-b608-bd560e89c7eb start:2016-09-07 00:49:07.836
task96ebb6ca-c99b-482e-b608-bd560e89c7eb end:2016-09-07 00:49:09.837
task1ce9f4bb-dd9e-4510-a697-73daef02fe6b start:2016-09-07 00:49:09.837
task1ce9f4bb-dd9e-4510-a697-73daef02fe6b end:2016-09-07 00:49:11.837
task0386a855-3e85-4d06-9d91-24abde228731 start:2016-09-07 00:49:11.837
task0386a855-3e85-4d06-9d91-24abde228731 end:2016-09-07 00:49:13.838
task886fe541-92d1-49bc-b5bd-2c425cf773ba start:2016-09-07 00:49:13.838
task886fe541-92d1-49bc-b5bd-2c425cf773ba end:2016-09-07 00:49:15.838
task460137d1-7daf-419b-b0d5-87f31833176c start:2016-09-07 00:49:15.838
task460137d1-7daf-419b-b0d5-87f31833176c end:2016-09-07 00:49:17.838
taskce78bffb-8151-46e8-81d9-57b01e9294a2 start:2016-09-07 00:49:17.838
taskce78bffb-8151-46e8-81d9-57b01e9294a2 end:2016-09-07 00:49:19.838
task1fad4b4f-4143-4098-943a-c894ad96ae58 start:2016-09-07 00:49:19.838
task1fad4b4f-4143-4098-943a-c894ad96ae58 end:2016-09-07 00:49:21.838
taskc5de2fab-0688-4410-9408-b0990cc76223 start:2016-09-07 00:49:21.838
taskc5de2fab-0688-4410-9408-b0990cc76223 end:2016-09-07 00:49:23.838
task7dccb95b-6088-4a5d-a2e0-edb4381f7d0c start:2016-09-07 00:49:23.838
task7dccb95b-6088-4a5d-a2e0-edb4381f7d0c end:2016-09-07 00:49:25.838
taskc05908b5-1bb2-496a-9ddc-c3939d783f2c start:2016-09-07 00:49:25.838
taskc05908b5-1bb2-496a-9ddc-c3939d783f2c end:2016-09-07 00:49:27.839
task251c4102-f214-4eb9-9e13-7ca7f2eb3362 start:2016-09-07 00:49:27.839
task251c4102-f214-4eb9-9e13-7ca7f2eb3362 end:2016-09-07 00:49:29.839
task645f6f0f-9d11-4545-be12-1feab67a6b06 start:2016-09-07 00:49:29.839
task645f6f0f-9d11-4545-be12-1feab67a6b06 end:2016-09-07 00:49:31.84
task82da54a5-6620-46f4-a840-10633555d2e8 start:2016-09-07 00:49:31.84
task82da54a5-6620-46f4-a840-10633555d2e8 end:2016-09-07 00:49:33.84
taskb33558c1-cb84-4724-85af-ac8060b169a0 start:2016-09-07 00:49:33.84