【保姆级示例向】观察者模式
案例来自《重学Java设计模式》
案例场景
本案例是模拟每次小客车摇号通知的场景，如下图（截自《重学Java设计模式》）
文件结构
完整代码
EventListener.java
这个接口定义了监听事件要执行的方法，后面创建的监听器都会实现这个接口并重写该方法
public interface EventListener < T > {
/**
* observed do
* @param type
*/
void doEvent ( T type ) ;
}
MessageEventListener.java
消息监听器，用于监听摇号结果并给用户发送通知结果的消息（此处用日志模拟发送短信）
public class MessageEventListener implements EventListener < LotteryResult > {
public static Logger logger = LoggerFactory.getLogger( MessageEventListener.class ) ;
@Override
public void doEvent ( LotteryResult lotteryResult ) {
logger.info ( "给用户 {} 发送通知：{}",lotteryResult.getUid () ,lotteryResult.getMessage ()) ;
}
}
MQEventListener.java
消息队列监听器，用于监听摇号结果并记录结果（此处用日志模拟发送短信）
public class MQEventListener implements EventListener < LotteryResult > {
public static Logger logger = LoggerFactory.getLogger( MQEventListener.class ) ;
@Override
public void doEvent ( LotteryResult lotteryResult ) {
logger.info ( "记录用户 {} 摇号结果：{}",lotteryResult.getUid () ,lotteryResult.getMessage ()) ;
}
}
EventManager.java
这里定义了一个存储监听器的集合listeners以及监听类型的枚举类EventType，并封装了操作监听器的方法：
-
订阅方法：
subscribe() -
取消订阅方法：
unsubscribe() -
通知方法：
notify()
public class EventManager {
Map < Enum < EventType > , List < EventListener >> listeners = new HashMap <>() ;
public EventManager ( Enum < EventType > ... operations ) {
for ( Enum < EventType > operation : operations ) {
this.listeners.put ( operation, new ArrayList <>()) ;
}
}
/**
* 事件类型枚举类
*/
public enum EventType {
MQ, Message
}
/**
* 订阅
*
* @param eventType 事件类型
* @param listener 监听
*/
public void subscribe ( Enum < EventType > eventType, EventListener listener ) {
/**
* 将新订阅的监听器添加进存储不同监听器的map中
*/
List < EventListener > users = listeners.get ( eventType ) ;
users.add ( listener ) ;
}
/**
* 取消订阅
*
* @param eventType 事件类型
* @param listener 监听
*/
public void unsubscribe ( Enum < EventType > eventType, EventListener listener ) {
List < EventListener > users = listeners.get ( eventType ) ;
users.remove ( listener ) ;
}
/**
* 通知
*
* @param eventType 事件类型
* @param lotteryResult 通知结果
*/
public void notify ( Enum < EventType > eventType, LotteryResult lotteryResult ) {
List < EventListener > users = listeners.get ( eventType ) ;
for ( EventListener user : users ) {
user.doEvent ( lotteryResult ) ;
}
}
}
LotteryResult.java
这个对象封装了返回所需要的信息
@Data
public class LotteryResult {
String uid;
String message;
Date time;
public LotteryResult ( String uid, String message, Date time ) {
this.uid = uid;
this.message = message;
this.time = time;
}
}
LotteryService.java
这里依赖了EventManager这个操作监听器的方法类
-
构造函数中执行了监听器订阅操作
-
在调用
draw()方法中执行了监听器的通知操作（针对此示例可以理解为监听器的监听对象执行事件draw()时，会通知监听器(MessageEventListener和MQEventListener)，此时监听器会遍历执行监听器中定义的doEvent()方法） -
定义了一个实际处理主线业务逻辑的
doDraw()方法交由子类去实现
public abstract class LotteryService {
private EventManager eventManager;
public LotteryService () {
eventManager = new EventManager ( EventManager.EventType.MQ, EventManager.EventType.Message) ;
eventManager.subscribe ( EventManager.EventType.MQ, new MQEventListener ()) ;
eventManager.subscribe ( EventManager.EventType.Message, new MessageEventListener ()) ;
}
public LotteryResult draw ( String uid ) {
LotteryResult lotteryResult = doDraw ( uid ) ;
eventManager.notify ( EventManager.EventType.MQ, lotteryResult ) ;
eventManager.notify ( EventManager.EventType.Message, lotteryResult ) ;
return lotteryResult;
}
protected abstract LotteryResult doDraw ( String uid ) ;
}
LotteryServiceImpl.java
调用当前案例的主线业务逻辑：小客车摇号
package com.aqin.listenerpattern;
import java.util.Date;
/**
* @Description
* @Author aqin1012 AQin.
* @Date 2022/8/2 1:31 PM
* @Version 1.0
*/
public class LotteryServiceImpl extends LotteryService {
MinibusTargetService minibusTargetService = new MinibusTargetService () ;
@Override
protected LotteryResult doDraw ( String uid ) {
String lottery = minibusTargetService.lottery ( uid ) ;
return new LotteryResult ( uid, lottery, new Date ()) ;
}
}
MinibusTargetService.java
封装了小客车的相关操作
-
目前只有一个摇号服务，后续如有业务扩展，直接在此类中添加
-
如果有别的车型则新建该车型的类即可
package com.aqin.listenerpattern;
/**
* @Description
* @Author aqin1012 AQin.
* @Date 2022/8/2 3:55 PM
* @Version 1.0
*/
public class MinibusTargetService {
/**
* mock lottery
*
* @param uid
* @return
*/
public String lottery ( String uid ) {
return Math.abs( uid.hashCode () % 2 ) == 0 ? "中签" : "未中签";
}
}
pom.xml
这个示例项目需要添加下依赖
< project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" >
< modelVersion > 4.0.0
< groupId > org.example
< artifactId > Desigins
< version > 1.0-SNAPSHOT
< properties >
< maven.compiler.source > 8
< maven.compiler.target > 8
< dependencies >
< dependency >
< groupId > org.projectlombok
< artifactId > lombok
< version > 1.18.0
< dependency >
< groupId > org.slf4j
< artifactId > slf4j-api
< version > 1.7.25
< dependency >
< groupId > ch.qos.logback
< artifactId > logback-classic
< version > 1.2.3
< dependency >
< groupId > org.junit.jupiter
< artifactId > junit-jupiter-api
< version > 5.2.0
< scope > test
测试
测试代码
package com.aqin.listenerpattern;
import lombok.extern.slf4j.Slf4j;
/**
* @Description
* @Author aqin1012 AQin.
* @Date 2022/8/2 4:09 PM
* @Version 1.0
*/
@Slf4j
public class Test {
@org.junit.jupiter.api.Test
public void test_draw () {
LotteryService lotteryService = new LotteryServiceImpl () ;
LotteryResult result = lotteryService.draw ( "233444449484441" ) ;
System.out.println ( result ) ;
}
}