10.Callable与Future的应用

import java.util.Random;
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;
import java.util.concurrent.Future;

/**
 * Callable与Future的应用
 * Future取得的结果类型和Callable返回的结果类型必须一致，这是通过泛型来实现。
 * Callable要采用ExecutorService的submit方法提交，返回的future对象可以取消任务。
 * 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。
 * @author LiTaiQing
 *
 */
public class CallableAndFuture {
    
    public static void main(String[] args) {
        
        ExecutorService threadPool = Executors.newSingleThreadExecutor();
        Future<String> future = 
        //有返回结果时用submit
        threadPool.submit(new Callable<String>(){
            @Override
            public String call() throws Exception {
                return "Hello";
            }
            
        });
        
        System.out.println("等待结果");
        try {
            System.out.println("拿到结果" + future.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        
        ExecutorService threadPool2 = Executors.newFixedThreadPool(10);
        CompletionService<Integer> completionService = new ExecutorCompletionService<Integer>(threadPool2);
        for(int i = 1; i < 10; i++){
            final int seq = i;
            completionService.submit(new Callable<Integer>(){
                @Override
                public Integer call() throws Exception {
                    Thread.sleep(new Random().nextInt(5000));
                    return seq;
                }
                
            });
        }
        
        for(int i = 0 ; i < 10; i++){
            try {
                System.out.println(completionService.take().get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            };
        }
        
    }
    
}