回调机制

回调机制运用什么场景?

1、当你正在做事，但有个信息需要别人通知你，那个人很忙说你留个电话我，有消息我就通知你，你继续干你的事，两不误。可以解决阻塞问题。

 

2、在某个条件满足后去执行未知的逻辑，因为未知，所以预留接口待外界传入类，有点模板方法的意思。这个可以解耦。

 

写一个例子：

 

场景：某员工正在拍卖现场出价，老板说：你按我的指示出价，如果我有变动会通知你，你再改变出价。

分析：员工要不停的出价，不能因为等待老板的电话而停止出价。我们将员工实现callback接口，注入另外个线程，当老板有电话时将信息传入员工，这样不会影响员工工作。

 

代码：

package my.test.callback;

/**
 * 
 * 描述 回调接口
 *
 * @author 锅巴
 * @version 1.0 2010-10-15
 */
public interface IMessageCallBack {

    void receiveMessage(String message);
}

 

 

package my.test.callback;

/**
 * 
 * 描述 员工并实现回调接口
 *
 * @author 锅巴
 * @version 1.0 2010-10-15
 */
public class Employee implements IMessageCallBack{
    
    private int value = 8888;
    
    /**
     * 不断的出价
     */
    public void doWork(){  
        while(true){
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("value:" + value);
        }
    }
    
    
    

    /**
     * 回调方法,接收老板指令
     */
    public void receiveMessage(String message) {
        // TODO Auto-generated method stub
        value = Integer.parseInt(message);
    }
}

 

package my.test.callback;

import java.util.Random;

import org.springframework.beans.factory.InitializingBean;


/**
 * 
 * 消息监听器
 *
 * @author 锅巴
 * @version 1.0 2010-10-15
 */
public class Messagelisten implements InitializingBean{

    private IMessageCallBack messageCallBack;
    
    public void init(){
          (new Thread(new MessageCreate(messageCallBack))).start();
    }

    public void setMessageCallBack(IMessageCallBack messageCallBack) {
        this.messageCallBack = messageCallBack;
    }

    public void afterPropertiesSet() throws Exception {
        // TODO Auto-generated method stub
        if(messageCallBack == null){
            throw new IllegalAccessException("error: messageCallBack is null");
        }
    }  
}


class MessageCreate implements Runnable{

    
    private IMessageCallBack messageCallBack;
    
    public MessageCreate(IMessageCallBack messageCallBack){
        this.messageCallBack = messageCallBack;
    }
    
    public void run() {
        // TODO Auto-generated method stub
        String message = null;
        while((message = listen()) != null){
            messageCallBack.receiveMessage(message);
            
        }
    }
    
    private String listen(){
        
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("---------- listen -----------");
        Random random = new Random();
        if(random.nextInt(10) > 5){
            return String.valueOf(random.nextInt(10000));
        }
        return null;
    }
    
}

 

配置文件

<bean id="employee" class="my.test.callback.Employee"/>
	
<bean id="messagelisten" class="my.test.callback.Messagelisten" init-method="init">
	<property name="messageCallBack" ref="employee"/>
</bean>

 

Test

  

package my.test.user.api;

import my.test.callback.Employee;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class CallBackTest {

    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("callback.context.xml");
        Employee employee = (Employee)context.getBean("employee");
        employee.doWork();
    }
}