Future and Callable

• 1. Runnable的缺陷
• 2.Callable接口
• 3. Future类
• 4. 用法1： 线程池的submit方法返回Future对象
• 5. 用法2： 用FutureTask来创建Future
• 6.Future的注意点

1. Runnable的缺陷

1. 不能返回一个返回值
2. 不能抛出异常

2.Callable接口

3. Future类

4. 用法1： 线程池的submit方法返回Future对象

/**
 * @Classname OneFuture
 * @Description 演示一个Future的简单使用方法
 * @Date 2021/3/1 16:52
 * @Created by YoungLiu
 */
public class OneFuture {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService service = Executors.newFixedThreadPool(10);
        Future<Integer> future = service.submit(new CallableTask());
        System.out.println(future.get());
    }

    static class CallableTask implements Callable<Integer>{

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

}

/**
 * @Classname OneFuture
 * @Description 演示一个Future的简单使用方法,Lambda
 * @Date 2021/3/1 16:52
 * @Created by YoungLiu
 */
public class OneFutureLambda {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService service = Executors.newFixedThreadPool(10);
        Callable<Integer> callable = ()->{
            Thread.sleep(3000);
            return new Random().nextInt();
        };
        Future<Integer> future = service.submit(callable);
        System.out.println(future.get());
    }

}

/**
 * @Classname MultiFutures
 * @Description 演示批量提交任务时，用List来批量接收任务
 * @Date 2021/3/1 17:02
 * @Created by YoungLiu
 */
public class MultiFutures {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService service = Executors.newFixedThreadPool(2);
        ArrayList<Future> futures = new ArrayList<>();
        for (int i = 0; i < 20; i++) {
            Future<Integer> future = service.submit(new CallableTask());
            futures.add(future);
        }
        Thread.sleep(5000);
        for (int i = 0; i < 20; i++) {
            Future<Integer> future = futures.get(i);
            Integer j =(Integer) future.get();
            System.out.println(j);
        }
    }
    static class CallableTask implements Callable<Integer>{

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

/**
 * @Classname Timeout
 * @Description 演示get的超时方法，需要注意超时后处理，调用future.cancel()。
 * 演示cancel传入true和false的区别，代表是否中断正在执行的任务。
 * @Date 2021/3/1 17:35
 * @Created by YoungLiu
 */
public class Timeout {
    private static final Ad DEFAULT_AD = new Ad("无网络时候的默认公司");
    private static final ExecutorService service = Executors.newFixedThreadPool(10);


    static class Ad {
        String name;

        public Ad(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return "Ad{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }

    static class FetchAdTask implements Callable<Ad> {

        @Override
        public Ad call() throws Exception {
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                System.out.println("sleep期间被中断");

                return new Ad("被中断时候的默认广州");
            }

            return new Ad("旅游订票哪家强？找xx");
        }
    }

    public void printAd() {
        Future<Ad> f = service.submit(new FetchAdTask());
        Ad ad;
        try {
            ad = (Ad) f.get(2000, TimeUnit.MILLISECONDS);
        } catch (InterruptedException e) {
            ad = new Ad("被中断时候的默认广告");
            e.printStackTrace();
        } catch (ExecutionException e) {
            ad = new Ad("异常时候的默认广州");
            e.printStackTrace();
        } catch (TimeoutException e) {
            ad = new Ad("超时时候的默认广告");
            System.out.println("超时，为了获取到广告");
            //取消成功 返回true 取消失败 false
            boolean cancel = f.cancel(false);//如果参数是true，会把线程中断
            System.out.println("cancel的结果" + cancel);
        }
        service.shutdown();
        System.out.println(ad);
    }


    public static void main(String[] args) {
        Timeout timeout = new Timeout();
        timeout.printAd();
    }
}

5. 用法2： 用FutureTask来创建Future

/**
 * @Classname FutureTaskDemo
 * @Description 演示FutureTask的用法
 * @Date 2021/3/1 18:08
 * @Created by YoungLiu
 */
public class FutureTaskDemo {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Task task = new Task();
        FutureTask<Integer> integerFutureTask = new FutureTask<>(task);
//        new Thread(integerFutureTask).start();
        ExecutorService service = Executors.newFixedThreadPool(10);
        service.submit(integerFutureTask);

        Integer integer = integerFutureTask.get();
        System.out.println("futuretask运行结果"+integer);
    }

    static class Task implements Callable<Integer>{

        @Override
        public Integer call() throws Exception {
            System.out.println("子线程正在计算");
            Thread.sleep(3000);
            int sum=0;
            for (int i = 0; i < 100; i++) {
                sum+=i;
            }
            return sum;
        }
    }
}

6.Future的注意点