JDK6新特性 ExecutorCompletionSe

Question

Java的并发库 的CompletionService 可以满足这种场景要求。该接口有两个重要方法：submit()和take()。submit用于提交一个runnable或者callable，一般会提交给一个线程池处理；而take就是取出已经执行完毕runnable或者callable实例的Future对象，如果没有满足要求的，就等待了。 CompletionService还有一个对应的方法poll，该方法与take类似，只是不会等待，如果没有满足要求，就返回null对象。package 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;
import java.util.concurrent.Future;public class TestCompletionService
{
    public static void main(String[] args)
        throws InterruptedException, ExecutionException
    {
        ExecutorService exec = Executors.newFixedThreadPool(10);
        CompletionService<String> serv = new ExecutorCompletionService<String>(exec);
        for (int index = 0; index < 5; index++)
        {
            final int NO = index;
            Callable<String> downImg = new Callable<String>()
            {
                public String call()
                    throws Exception
                {
                    Thread.sleep((long)(Math.random() * 10000));
                    return "Downloaded Image " + NO;
                }
            };
            serv.submit(downImg);
        }
        Thread.sleep(1000 * 2);
        
        System.out.println("Show web content");
        
        for (int index = 0; index < 5; index++)
        {
            Future<String> task = serv.take();
            String img = task.get();
            System.out.println(img);
        }
        System.out.println("End");
        // 关闭线程池
        exec.shutdown();
    }
}