CompletionService

 
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();  
      }  
    }