异步回调

雨点打透心脏的1/2处 2021-10-23 16:34 327阅读 0赞

# 异步回调 #

2019-08-14

**目录**

1 回调  
2 使用wait和notify方法实现异步回调  
3 使用CountDownLatch实现异步回调

### 1 回调 ###

--------------------

回调的思想是：

*  **类A的a()方法调用类B的b()方法**
 *  **类B的b()方法执行完毕主动调用类A的callback()方法**

**![484791-20190814140926356-1999340331.png][]**

### 2 使用wait和notify方法实现异步回调 ###

--------------------

ICallback代码：

public interface ICallback {
        void callback(long response);
    }

AsyncCallee代码：

import java.util.Random;
    
    public class AsyncCallee {
        private Random random = new Random(System.currentTimeMillis());
    
        public void doSomething(ICallback iCallback){
            new Thread(()->{
                long res = random.nextInt(4);
    
                try {
                    Thread.sleep(res*1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
    
                iCallback.callback(res);
            }).start();
        }
    }

Caller1代码：

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][]

public class Caller1 implements ICallback{
        private final Object lock = new Object();
        AsyncCallee callee;
        public Caller1(AsyncCallee asyncCallee){
            callee=asyncCallee;
        }
    
        public void callback(long response) {
            System.out.println("得到结果");
            System.out.println(response);
            System.out.println("调用结束");
    
            synchronized (lock) {
                lock.notifyAll();
            }
        }
    
        public void call(){
            System.out.println("发起调用");
            callee.doSomething(this);
            System.out.println("调用返回");
        }
    
        public static void main(String[] args) {
            AsyncCallee asyncCallee=new AsyncCallee();
            Caller1 demo1 = new Caller1(asyncCallee);
            demo1.call();
    
            synchronized (demo1.lock){
                try {
                    demo1.lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
    
            System.out.println("主线程内容");
        }
    }

### 3 使用CountDownLatch实现异步回调 ###

--------------------

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][]

import java.util.concurrent.CountDownLatch;
    
    public class Caller2 implements ICallback{
        private final CountDownLatch countDownLatch = new CountDownLatch(1);
        AsyncCallee callee;
        public Caller2(AsyncCallee asyncCallee){
            callee=asyncCallee;
        }
    
        @Override
        public void callback(long response) {
            System.out.println("得到结果");
            System.out.println(response);
            System.out.println("调用结束");
    
            countDownLatch.countDown();
        }
    
        public void call(){
            System.out.println("发起调用");
            callee.doSomething(this);
            System.out.println("调用返回");
        }
    
    
        public static void main(String[] args) {
            AsyncCallee asyncCallee=new AsyncCallee();
            Caller2 demo4 = new Caller2(asyncCallee);
            demo4.call();
    
            try {
                demo4.countDownLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
    
            System.out.println("主线程内容");
        }
    }

转载于:https://www.cnblogs.com/Ming8006/p/11351647.html

[484791-20190814140926356-1999340331.png]: /images/20211023/4a2d54ce7bb940cfb68a49baa0fe58dd.png
[ContractedBlock.gif]: https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif
[ExpandedBlockStart.gif]: /images/20211023/fc5ea1f4b700499fa1721ff0f146e8bd.png