【JUC】4-FutrueTask结合线程池的应用

1、通过线程池提交FutrueTask异步任务

public static void main(String[] args) throws ExecutionException, InterruptedException, TimeoutException {

        long start = System.currentTimeMillis();
        ExecutorService executorService = Executors.newFixedThreadPool(3);

        FutureTask<String> futureTask1 = new FutureTask<>(() -> {
            TimeUnit.SECONDS.sleep(3);
            return "futureTask1";
        });

        executorService.submit(futureTask1);

        FutureTask<String> futureTask2 = new FutureTask<>(() -> {
            TimeUnit.SECONDS.sleep(10);
            return "futureTask2";
        });
        executorService.submit(futureTask2);
        FutureTask<String> futureTask3 = new FutureTask<>(() -> {
            TimeUnit.SECONDS.sleep(4);
            return "futureTask3";
        });
        executorService.submit(futureTask3);

        // 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
        System.out.println(futureTask1.get());
        System.out.println(futureTask2.get());
        System.out.println(futureTask3.get());
        // 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
        // get()方法一般放在程序后面
        // 或者指定等待时间
        System.out.println(futureTask2.get(3, TimeUnit.SECONDS)); // 会抛出异常

        executorService.shutdown();

        long end = System.currentTimeMillis();

        System.out.println(end - start);
    }

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

public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(3);
        try {
            FutureTask<String> futureTask = new FutureTask<>(() -> {
                TimeUnit.SECONDS.sleep(5);
                return "futureTask";
            });

            executorService.submit(futureTask);

            System.out.println("执行其他任务...");

            // 轮询耗费资源
            while (true) {
                if (futureTask.isDone()) {
                    System.out.println(futureTask.get());
                    break;
                } else {
                    TimeUnit.MILLISECONDS.sleep(500);
                    System.out.println("程序处理中，勿催");
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            executorService.shutdown();
        }
    }