Future设计模式

 Future设计模式把同步调用变成异步调用

//表示一个可能还没有完成的异步任务的结果，直接返回给调用者
public interface Future<T> {

    T get() throws InterruptedException;

}

//Future具体的实现
public class AsynFuture<T> implements Future<T> {

    private volatile boolean done = false;

    private T result;

    public void done(T result) {
        synchronized (this) {
            this.result = result;
            this.done = true;
            this.notifyAll();
        }
    }

    @Override
    public T get() throws InterruptedException {
        synchronized (this) {
            while (!done) {
                this.wait();
            }
        }
        return result;
    }
}

//要提交的异步任务，执行逻辑由子类覆写call方法
public interface FutureTask<T> {

    T call();
}

//桥接Future和FutureTask
public class FutureService {

    //调用者通过Future来获取结果
    public <T> Future<T> submit(final FutureTask<T> task) {
        AsynFuture<T> asynFuture = new AsynFuture<>();
        new Thread(() -> {
            T result = task.call();
            asynFuture.done(result);
        }).start();
        return asynFuture;
    }

  //调用者通过Future来获取结果或者由回调函数来处理
    public <T> Future<T> submit(final FutureTask<T> task, final Consumer<T> consumer) {
        AsynFuture<T> asynFuture = new AsynFuture<>();
        new Thread(() -> {
            T result = task.call();
            asynFuture.done(result);
            consumer.accept(result);
        }).start();
        return asynFuture;
    }
}

public class Client {

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

        FutureService futureService = new FutureService();
        //通过回调函数通知调用者
//        futureService.submit(() -> {
//            try {
//                Thread.sleep(10000L);
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
//            return "FINISH";
//        }, System.out::println);

        //调用者主动获取结果，可能会发生阻塞
        Future<String> future = futureService.submit(()->{
            try {
                Thread.sleep(5000L);
            }catch(Exception e) {
                e.printStackTrace();
            }
            return "ABC";
        });
        
        System.out.println("===========");
        Thread.sleep(2000);
        System.out.println("######## "+future.get());
    }
}