【JUC】4-FutrueTask结合线程池的应用

1、通过线程池提交FutrueTask异步任务

 1 public static void main(String[] args) throws ExecutionException, InterruptedException, TimeoutException {
 2 
 3         long start = System.currentTimeMillis();
 4         ExecutorService executorService = Executors.newFixedThreadPool(3);
 5 
 6         FutureTask<String> futureTask1 = new FutureTask<>(() -> {
 7             TimeUnit.SECONDS.sleep(3);
 8             return "futureTask1";
 9         });
10 
11         executorService.submit(futureTask1);
12 
13         FutureTask<String> futureTask2 = new FutureTask<>(() -> {
14             TimeUnit.SECONDS.sleep(10);
15             return "futureTask2";
16         });
17         executorService.submit(futureTask2);
18         FutureTask<String> futureTask3 = new FutureTask<>(() -> {
19             TimeUnit.SECONDS.sleep(4);
20             return "futureTask3";
21         });
22         executorService.submit(futureTask3);
23 
24         // 获取结果才是等待线程执行完成，如果不获取结果只是提交了任务
25         System.out.println(futureTask1.get());
26         System.out.println(futureTask2.get());
27         System.out.println(futureTask3.get());
28         // FutrueTask接口一旦调用了get()方法，就会一直等待计算结果，容易造成线程阻塞
29         // get()方法一般放在程序后面
30         // 或者指定等待时间
31         System.out.println(futureTask2.get(3, TimeUnit.SECONDS)); // 会抛出异常
32 
33         executorService.shutdown();
34 
35         long end = System.currentTimeMillis();
36 
37         System.out.println(end - start);
38     }

2、轮询获取FutrueTask的处理结果

要想FutrueTask的任务尽量不阻塞其他线程任务，应该把get()放到后面，并且采用轮询的方法获取计算结果

 1 public static void main(String[] args) {
 2         ExecutorService executorService = Executors.newFixedThreadPool(3);
 3         try {
 4             FutureTask<String> futureTask = new FutureTask<>(() -> {
 5                 TimeUnit.SECONDS.sleep(5);
 6                 return "futureTask";
 7             });
 8 
 9             executorService.submit(futureTask);
10 
11             System.out.println("执行其他任务...");
12 
13             // 轮询耗费资源
14             while (true) {
15                 if (futureTask.isDone()) {
16                     System.out.println(futureTask.get());
17                     break;
18                 } else {
19                     TimeUnit.MILLISECONDS.sleep(500);
20                     System.out.println("程序处理中，勿催");
21                 }
22             }
23 
24         } catch (Exception e) {
25             e.printStackTrace();
26         } finally {
27             executorService.shutdown();
28         }
29     }