Java线程之FutureTask与Future浅析

一、Future使用

        FutureTask是Future和Callable的结合体。传统的代码是这样写的

        Future f = executor.submit(new Callable());

        然后通过Future来取得计算结果。但是,若开启了多个任务,我们无从知晓哪个任务最先结束。因此,若要实现“当某任务结束时,立刻做一些事情,例如记录日志”这一功能,就需要写一些额外的代码。例如一般的Future使用。

多任务:

 1 package zmx.multithread.test.reentrantlock;
 2  
 3  
 4 import java.util.Random;
 5 import java.util.concurrent.Callable;
 6 import java.util.concurrent.ExecutionException;
 7 import java.util.concurrent.ExecutorService;
 8 import java.util.concurrent.Executors;
 9 import java.util.concurrent.Future;
10 import java.util.concurrent.FutureTask;
11 import java.util.concurrent.TimeUnit;
12  
13 public class T1 {
14     public static void main(String[] args) throws InterruptedException, ExecutionException {
15             
16          ExecutorService executor2= Executors.newFixedThreadPool(5);          
17          class Task implements Callable<String>{
18             @Override
19             public String call() throws Exception {
20                 
21                 Random rand = new Random();  
22                 TimeUnit.SECONDS.sleep(rand.nextInt(10));  
23                 return  Thread.currentThread().getName();
24             }             
25          }
26          
27          List<Future<String>> results = new ArrayList<Future<String>>();
28          for(int i=0;i<5;i++){
29              Future<String> f =  executor2.submit(new Task());
30              results.add(f);
31          }
32  
33          boolean flag =true; 
34          while(flag) {
35             
36             for(Iterator<Future<String>> iter  = results.iterator();iter.hasNext();){
37                 Future<String> f =iter.next();
38                 if(f.isDone()){
39                     System.out.println(f.get());
40                     iter.remove();
41                     
42                 }
43             }
44             if(results.size()==0){
45                 flag =false;
46             }
47             
48         }
49         
50         System.out.println("执行完毕");
51          
52         executor2.shutdownNow();
53          
54          
55          
56     }
57  
58 }

执行结果:

pool-1-thread-4
pool-1-thread-2
pool-1-thread-1
pool-1-thread-5
pool-1-thread-3
执行完毕

 

二、FutureTask

      上述使用遍历的方式解决多任务结果,但是不是最优的效果,FutureTask正是为此而存在,它有一个回调函数protected void done(),当任务结束时,该回调函数会被触发。因此,只需重载该函数,即可实现在线程刚结束时就做一些事情。

代码如下:

 1 public class Test {
 2     public static void main(String[] args) {
 3         ExecutorService executor = Executors.newCachedThreadPool();
 4         for(int i=0; i<5; i++) {
 5             Callable<String> c = new Task();
 6             MyFutureTask ft = new MyFutureTask(c);
 7             executor.submit(ft);
 8         }
 9         executor.shutdown();
10     }
11         
12 }
13  
14 class MyFutureTask extends FutureTask<String> {
15  
16     public MyFutureTask(Callable<String> callable) {
17         super(callable);
18     }
19  
20     @Override
21     protected void done() {
22         try {
23             System.out.println(get() + " 线程执行完毕!~");
24         } catch (InterruptedException | ExecutionException e) {
25             // TODO Auto-generated catch block
26             e.printStackTrace();
27         }
28     }
29     
30     
31 }
32  
33 class Task implements Callable<String> {
34  
35     @Override
36     public String call() throws Exception {
37         Random rand = new Random();
38         TimeUnit.SECONDS.sleep(rand.nextInt(12));
39         return Thread.currentThread().getName();
40     }
41 }

结果如下:

pool-1-thread-4 线程执行完毕!
pool-1-thread-3 线程执行完毕!
pool-1-thread-5 线程执行完毕!
pool-1-thread-2 线程执行完毕!
pool-1-thread-1 线程执行完毕!

posted @ 2018-08-21 14:00  浅滩沙洲  阅读(2619)  评论(0编辑  收藏  举报