Java并发编程-Future的使用

Future顾名思义，未来

public class FutureDemo3 implements Callable<Integer> {
    public static void main(String[] args) {
        ExecutorService executorService= Executors.newFixedThreadPool(16);
        Future<Integer>future=executorService.submit(new FutureDemo3());
        try {
            System.out.println(future.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        System.out.println("程序执行结束");
    }

    @Override
    public Integer call() throws Exception {
        Thread.sleep(3000);
        return new Random().nextInt();
    }
}

future还有isDone方法，表示是否做完。

public class FutureDemo3 implements Callable<Integer> {
    public static void main(String[] args) {
        ExecutorService executorService= Executors.newFixedThreadPool(16);
        Future<Integer>future=executorService.submit(new FutureDemo3());
        System.out.println(future.isDone());
        try {
            System.out.println(future.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        System.out.println("程序执行结束");
        System.out.println(future.isDone());
    }
    @Override
    public Integer call() throws Exception {
        Thread.sleep(3000);
        return new Random().nextInt();
    }
}

false
2129310471
程序执行结束
true

线程池执行了callable的对象，后抛出异常，isDone还会不会是true呢

public class FutureExceptionDemo implements Callable<Integer> {
    public static void main(String[] args) {
        ExecutorService executorService= Executors.newFixedThreadPool(16);

        Future<Integer>future=executorService.submit(new FutureExceptionDemo());
            try {
                System.out.println(future.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
            System.out.println("程序执行结束");
            System.out.println(future.isDone());
    }
    @Override
    public Integer call() throws Exception {
        throw new Exception("终止进行");
    }
}

运行结果是：

java.util.concurrent.ExecutionException: java.lang.Exception: 终止进行
at java.util.concurrent.FutureTask.report(FutureTask.java:122)
at java.util.concurrent.FutureTask.get(FutureTask.java:192)
at com.company.FutureDemo.FutureExceptionDemo.main(FutureExceptionDemo.java:12)
Caused by: java.lang.Exception: 终止进行
at com.company.FutureDemo.FutureExceptionDemo.call(FutureExceptionDemo.java:25)
at com.company.FutureDemo.FutureExceptionDemo.call(FutureExceptionDemo.java:6)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
程序执行结束
true

可以看出的是，子线程在抛出异常是，isDone还是判断为True的。

FutureTask的使用

看一个案例

public class FutureTaskDemo2 implements Callable<Integer> {
    public static void main(String[] args) {
        FutureTask<Integer> futureTask = new FutureTask<>(new FutureTaskDemo2());
        new Thread(futureTask).start();
        try {
            System.out.println(futureTask.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
    }

    @Override
    public Integer call() throws Exception {
        System.out.println("子线程正在进行");
        Integer sum = 0;
        for (int i = 0; i < 100; i++) {
            sum += i;
        }
        return sum;
    }
}

这个案例将实现Callable接口的对象传入futureTask中，然后将FutureTask传入新创建的线程中，从FutureTask中取得相加所得到的值。