设计模式--发布者与订阅者

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Spring实现的发布者与订阅者  是观察者设计模式的一个扩展。

观察者设计模式

 

           目标

          观察者

          事件

三者之间是耦合在一起的，目标里面包含观察者的集合，观察者需要自己注入到目标中，当目标发生变化的时候，则会通知观察者集合，完成不同观察者的操作

 

 

发布者与订阅者的设计模式

 

发布者  订阅者  事件 事件通道

使用事件通道进行解决耦合的问题

Spring默认带有这个发布者关系

发布者 ApplicationContext

订阅者：@EventListener  ApplicationEventListener

事件：ApplicationEvent

通道：ApplicationEventMulticaster

一个使用Spring的demo

package designpattern.publisherandsubscribe;import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;@ComponentScan
public class Test {public static void main(String[] args){ApplicationContext context=new AnnotationConfigApplicationContext(Test.class);Test app=context.getBean(Test.class);RegisterService registerService=(RegisterService)context.getBean(RegisterService.class);registerService.regiesterUser();}
}

package designpattern.publisherandsubscribe;import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.core.task.SimpleAsyncTaskExecutor;@Configuration
public class AsyncEventConfig {@Bean(name = "applicationEventMulticaster")public ApplicationEventMulticaster simpleApplicationEventMulticaster() {SimpleApplicationEventMulticaster eventMulticaster= new SimpleApplicationEventMulticaster();eventMulticaster.setTaskExecutor(new SimpleAsyncTaskExecutor());return eventMulticaster;}
}

package designpattern.publisherandsubscribe;public interface EmailService {void sendEmail();
}

package designpattern.publisherandsubscribe;import org.springframework.context.event.EventListener;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Service;@Service
public class EmailServiceImpl implements EmailService {@Overridepublic void sendEmail() {System.out.println("send email");}@EventListenerpublic void receiveTradeEvent(TradeEvent<OrderModel> tradeEvent){OrderModel orderModel=tradeEvent.getEventData();System.out.println(orderModel.getOrderId()+"--"+orderModel.getCreateTime());System.out.println(Thread.currentThread().getId()+"--"+Thread.currentThread().getName());this.sendEmail();}}

package designpattern.publisherandsubscribe;public interface MobileService {String sendTelephone();
}

package designpattern.publisherandsubscribe;import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Service;@Service
public class MobileServiceImpl implements MobileService {@Overridepublic String sendTelephone() {System.out.println("发短信");return null;}@EventListenerpublic void receiveTradeEvent(TradeEvent<OrderModel> tradeEvent){OrderModel orderModel=tradeEvent.getEventData();System.out.println(orderModel.getOrderId()+"--"+orderModel.getCreateTime());System.out.println(Thread.currentThread().getId()+"--"+Thread.currentThread().getName());this.sendTelephone();}
}

package designpattern.publisherandsubscribe;import java.util.Date;public class OrderModel {private String orderId;private Date createTime;public String getOrderId() {return orderId;}public void setOrderId(String orderId) {this.orderId = orderId;}public Date getCreateTime() {return createTime;}public void setCreateTime(Date createTime) {this.createTime = createTime;}
}

package designpattern.publisherandsubscribe;public interface RegisterService {public void regiesterUser();
}

package designpattern.publisherandsubscribe;import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;import java.util.Date;@Service
public class RegisterServiceImpl implements RegisterService, ApplicationContextAware {private ApplicationContext applicationContext;@Override@Transactionalpublic void regiesterUser() {System.out.println("register user info to DB");OrderModel orderModel=new OrderModel();orderModel.setOrderId("111");orderModel.setCreateTime(new Date());applicationContext.publishEvent(new TradeEvent<OrderModel>(orderModel));System.out.println(Thread.currentThread().getId()+"--"+Thread.currentThread().getName());}@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {this.applicationContext=applicationContext;}
}

package designpattern.publisherandsubscribe;import org.springframework.context.ApplicationEvent;public class TradeEvent<T> extends ApplicationEvent {private T eventData;public TradeEvent(T source) {super(source);this.eventData=source;}public T getEventData() {return eventData;}public void setEventData(T eventData) {this.eventData = eventData;}
}

第二种发布者与订阅者的实现：分布式环境下的  消息中间件的使用，可以完成发布者和订阅者之间的关系，开源的产品notify，metaq，rocketmq，kafka。这些中间件还有一些其它的能力，比如发送消息和订阅消息，削峰填谷的能力，队列

 

第三种就是zookeeper的能力，也有发布订阅的能力。一个简单的case就是 如何实现DB热替换ip不宕机的需求

那就需要把配置文件的信息存储到 zookeeper的集群中，然后应用读取配置文件从zookeeper中读取，然后访问DB。应用程序需要启动zooker的客户端，连接zookeeper的服务端。

zookeeper还可以完成分布式锁，发布者和订阅者，领导选举等一些分布式的特性

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