Java多线程之线程并库Callable与Future的应用

示例：

 

package javaplay.thread.test;

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

public class CallableAndFuture {
	public static void main(String[] args) {
		ExecutorService threadPool = Executors.newSingleThreadExecutor();
		// 有返回结果的用submit 无返回结果的用execute
		Future<String> future = threadPool.submit(new Callable<String>() {

			@Override
			public String call() throws Exception {
				Thread.sleep(2000);
				return "hello";
			}

		});
		System.out.println("waiting result");
		try {
			// 超时就会抛异常
			System.out.println("result : " + future.get(1, TimeUnit.SECONDS));
		} catch (Exception e) {
			e.printStackTrace();
		}
		threadPool.shutdown();// 必须关闭 否则就一直在那等待 消耗资源 优良的编码习惯

		// CompletionService用于提交一组Callable任务，其take方法返回已完成的一个Callable任务对应的Future对象
		// 即哪个任务先完成了，就先获得哪个任务的执行结果
		ExecutorService threadPool2 = Executors.newFixedThreadPool(10);
		CompletionService<Integer> completionService = new ExecutorCompletionService<>(threadPool2);
		for (int i = 0; i < 10; i++) {// 提交10个任务
			final int seq = i;
			completionService.submit(new Callable<Integer>() {

				@Override
				public Integer call() throws Exception {
					Thread.sleep(new Random().nextInt(5000));
					return seq;
				}

			});
		}
		// 收获的季节
		for (int i = 0; i < 10; i++) {
			try {
				System.out.println(completionService.take().get());
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		threadPool2.shutdown();// 必须关闭
	}
}

实际应用中，一个Future代表一个任务的运行结果，任务多时可用ArrayList<Future>来代表多个任务的运行结果，再循环获取；