CompletionService

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");
	    //      
	    exec.shutdown();
	  }
	}