java 并发之Callable和Future

最新推荐文章于 2024-10-29 21:24:50 发布

Molise-tiansheng

最新推荐文章于 2024-10-29 21:24:50 发布

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分类专栏： java 文章标签： java 线程

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本文介绍了Java中Callable和Future的基本概念及使用方法，并通过两种不同方式展示了如何利用它们来执行并获取异步任务的结果。此外，还讲解了如何利用ExecutorService和CompletionService执行多个带有返回值的任务。

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Callable和Future，一个产生结果，一个拿到结果。

（1）一个返回值。

方式1

package com.thread;


import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;


public class CallableAndFuture {
     
	public static void main(String[] args) {
		//实现 callable 接口
		Callable<Integer> callable = new Callable<Integer>() {


			@Override
			public Integer call() throws Exception {
				// TODO Auto-generated method stub
				return new Random().nextInt(100);
			}
		};
		/* FutureTask 实现Future 和 Runnable 接口
		 * 实现FutureTask 用于接收Callable 返回的值
		 */
         FutureTask<Integer> futureTask = new FutureTask<Integer>(callable);
         new Thread(futureTask).start();
         
         try {
			Thread.sleep(5000);
		
				System.out.println(futureTask.get());
			} catch (ExecutionException e) {
				e.printStackTrace();
			}
		     catch (InterruptedException e) {
			e.printStackTrace();
		}
		
	}
}

方式2

package com.thread;

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;


public class ExecutorServiceAndFuture {
     
	public static void main(String[] args) {
		
		 ExecutorService executorService = Executors.newSingleThreadExecutor();
		 Future<Integer> future = executorService.submit(new Callable<Integer>() {

			@Override
			public Integer call() throws Exception {
				// TODO Auto-generated method stub
				return new Random().nextInt(100);
			}
		});
		 try {
			Thread.sleep(5000);
				System.out.println(future.get());
			} catch (ExecutionException e) {
				e.printStackTrace();
			}
		     catch (InterruptedException e) {
			    e.printStackTrace();
		}
		 
	}
	
}

（2）执行多个带返回值的任务

ExecutorService继承自Executor，它的目的是为我们管理Thread对象，从而简化并发编程，Executor使我们无需显示的去管理线程的生命周期，是JDK 5之后启动任务的首选方式。

package com.thread;

import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ExcutorServiceAndCompletionService {
	
     public static void main(String[] args) {
	      	
    	 ExecutorService executorService =Executors.newCachedThreadPool();
    	 
    	 CompletionService<Integer> cs = new ExecutorCompletionService<Integer>(executorService);
    	 
    	 for(int i=0; i<5;i++){
    		 final int taskID=i;
    		cs.submit(new Callable<Integer>() {
				
				@Override
				public Integer call() throws Exception {
					return taskID;
				}
			});
    		 
    	 }
    	 for(int i=0;i<5;i++){
    		 try {
				System.out.println(cs.take().get());
			} catch (InterruptedException e) {
				e.printStackTrace();
			} catch (ExecutionException e) {
				e.printStackTrace();
			}
    	 }
	}
}