【转载】Callable、FutureTask中阻塞超时返回的坑点

本文转载自：http://www.cnblogs.com/starcrm/p/5010863.html

案例1：

package com.net.thread.future;

import java.util.concurrent.Callable;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.FutureTask;

import java.util.concurrent.TimeUnit;

/**

 * @author

 * @Time：2017年8月18日 上午10:49:07

 * @version 1.0

 * @description

 */

  import java.util.concurrent.ExecutionException;

 import java.util.concurrent.ExecutorService;

 import java.util.concurrent.Executors;

 import java.util.concurrent.FutureTask;

 import java.util.concurrent.TimeUnit;

 import java.util.concurrent.TimeoutException;

 public class FutureTaskExample {

     public static void main(String[] args) {

         MyCallable callable1 = new MyCallable(1000);

         MyCallable callable2 = new MyCallable(5000);

         FutureTask<String> futureTask1 = new FutureTask<String>(callable1);

         FutureTask<String> futureTask2 = new FutureTask<String>(callable2);

         ExecutorService executor = Executors.newFixedThreadPool(2);

         executor.execute(futureTask1);

         executor.execute(futureTask2);

         while (true)

         {

             try {

                 if(futureTask1.isDone() && futureTask2.isDone()){

                     System.out.println("Done");

                     //shut down executor service

                     executor.shutdown();

                     return;

                 }

                 if(!futureTask1.isDone()){

                 //阻塞futureTask1

                 System.out.println("FutureTask1 output="+futureTask1.get());

                 }

                 if(!futureTask2.isDone()){

                 //阻塞futureTask2

                 System.out.println("FutureTask2 output="+futureTask2.get(1000,TimeUnit.MILLISECONDS));

                 }

             } catch (InterruptedException | ExecutionException e) {

                 e.printStackTrace();

             }catch(Exception e){

                 //do nothing

             }

         }

     }

     static class MyCallable implements Callable<String> {

         private long waitTime;

         public MyCallable(int timeInMillis){

             this.waitTime=timeInMillis;

         }

         @Override

         public String call() throws Exception {

             Thread.sleep(waitTime);

             return Thread.currentThread().getName();

         }

     }

 }

运行结果很简单，必须是：

FutureTask1 output=pool-1-thread-1
FutureTask2 output=pool-1-thread-2
Done

案例2：

package com.net.thread.future;

import java.util.concurrent.Callable;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

import java.util.concurrent.FutureTask;

import java.util.concurrent.TimeUnit;

/**

 * @author

 * @Time：2017年8月18日 上午10:49:07

 * @version 1.0

 * @description

 */

public class FutureTaskExample2 {

    public static void main(String[] args) {

        MyCallable callable1 = new MyCallable(1000);

        MyCallable callable2 = new MyCallable(5000);

        FutureTask<String> futureTask1 = new FutureTask<String>(callable1);

        FutureTask<String> futureTask2 = new FutureTask<String>(callable2);

        ExecutorService executor = Executors.newFixedThreadPool(2);

        executor.execute(futureTask1);

        executor.execute(futureTask2);

        while (true)

        {

             try {

                 if(futureTask1.isDone() && futureTask2.isDone()){

                     System.out.println("Done");

                     //shut down executor service

                     executor.shutdown();

                     return;

                 }

                 if(!futureTask1.isDone()){

                 //阻塞futureTask1

                 System.out.println("FutureTask1 output="+futureTask1.get());

                 }

                 System.out.println("Waiting for FutureTask2 to complete");

                 String s = futureTask2.get(1000, TimeUnit.MILLISECONDS); //阻塞500毫秒

                 if(s !=null){

                     System.out.println("FutureTask2 output="+s);

                 }

                 else{

                     System.out.println("FutureTask2 output is null");

                 }

             } catch (InterruptedException | ExecutionException e) {

                 e.printStackTrace();

             }catch(Exception e){

                 //do nothing

             }

        }

    }

    static class MyCallable implements Callable<String> {

        private long waitTime;

        public MyCallable(int timeInMillis){

            this.waitTime=timeInMillis;

        }

        @Override

        public String call() throws Exception {

            Thread.sleep(waitTime);

            return Thread.currentThread().getName();

        }

    }

}

运行结果：

FutureTask1 output=pool-1-thread-1
Waiting for FutureTask2 to complete
Waiting for FutureTask2 to complete
Waiting for FutureTask2 to complete
Waiting for FutureTask2 to complete
FutureTask2 output=pool-1-thread-2
Done

说明：

1、get()方法用来获取执行结果，这个方法会产生阻塞，会一直等到任务执行完毕才返回；

2、get(long timeout, TimeUnit unit)用来获取执行结果，如果超过指定时间，直接结束执行下面的代码；如果是在循环中，则跳出本次循环进行下一次轮训(continue功能类似)。

巴特西

【转载】Callable、FutureTask中阻塞超时返回的坑点

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