事件驱动模式

举个例子🌰

大部分软件或者APP都有会有会员系统，当我们注册为会员时，商家一般会把我们拉入会员群、给我们发优惠券、推送欢迎语什么的。

值得注意的是：

1. 注册成功后才会产生后面的这些动作；
2. 注册成功后的这些动作没有先后执行顺序之分；
3. 注册成功后的这些动作的执行结果不能互相影响；

传统写法

public Boolean doRegisterVip(){//1、注册会员registerVip();//2、入会员群joinMembershipGroup();//3、发优惠券issueCoupons();//4、推送消息sendWelcomeMsg();
}

这样的写法将所有的动作都耦合在doRegisterVip方法中，首先执行效率低下，其次耦合度太高，最后不好扩展。那么如何优化这种逻辑呢？

事件驱动模式原理介绍🍓

Spring的事件驱动模型由三部分组成：

事件：用户可自定义事件类和相关属性及行为来表述事件特征，Spring4.2之后定义事件不需要再显式继承ApplicationEvent类，直接定义一个bean即可，Spring会自动通过PayloadApplicationEvent来包装事件。

事件发布者：在Spring中可通过ApplicationEventPublisher把事件发布出去，这样事件内容就可以被监听者消费处理。

事件监听者：ApplicationListener，监听发布事件，处理事件发生之后的后续操作。

原理图如下：

代码实现

1. 定义基本元素

事件发布者：EventEngine.java、EventEngineImpl.java

package com.example.event.config;/*** 事件引擎*/
public interface EventEngine {/*** 发送事件** @param event 事件*/void publishEvent(BizEvent event);
}

package com.example.event.config;import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Executor;import org.springframework.util.CollectionUtils;/*** 事件引擎实现类*/
public class EventEngineImpl implements EventEngine {/*** 异步执行器。也系统需要自行定义线程池*/private Executor bizListenerExecutor;/*** 是否异步，默认为false*/private boolean async;/*** 订阅端 KEY是TOPIC，VALUES是监听器集合*/private Map> bizSubscribers = new HashMap<>(16);@Overridepublic void publishEvent(BizEvent event) {List listeners = bizSubscribers.get(event.getTopic());if (CollectionUtils.isEmpty(listeners)) {return;}for (BizEventListener bizEventListener : listeners) {if (bizEventListener.decide(event)) {//异步执行的话，放入线程池if (async) {bizListenerExecutor.execute(new EventSubscriber(bizEventListener, event));} else {bizEventListener.onEvent(event);}}}}/*** Setter method for property bizListenerExecutor.** @param bizListenerExecutor value to be assigned to property bizListenerExecutor*/public void setBizListenerExecutor(Executor bizListenerExecutor) {this.bizListenerExecutor = bizListenerExecutor;}/*** Setter method for property bizSubscribers.** @param bizSubscribers value to be assigned to property bizSubscribers*/public void setBizSubscribers(Map> bizSubscribers) {this.bizSubscribers = bizSubscribers;}/*** Setter method for property async.** @param async value to be assigned to property async*/public void setAsync(boolean async) {this.async = async;}
}

事件：BizEvent.java

package com.example.event.config;import java.util.EventObject;/*** 业务事件*/
public class BizEvent extends EventObject {/*** Topic*/private final String topic;/*** 业务id*/private final String bizId;/*** 数据*/private final Object data;/*** @param topic 事件topic，用于区分事件类型* @param bizId 业务ID，标识这一次的调用* @param data  事件传输对象*/public BizEvent(String topic, String bizId, Object data) {super(data);this.topic = topic;this.bizId = bizId;this.data = data;}/*** Getter method for property topic.** @return property value of topic*/public String getTopic() {return topic;}/*** Getter method for property id.** @return property value of id*/public String getBizId() {return bizId;}/*** Getter method for property data.** @return property value of data*/public Object getData() {return data;}
}

事件监听者：EventSubscriber.java

package com.example.event.config;/*** 事件监听者。注意：此时已经没有线程上下文，如果需要请修改构造函数，显示复制上下文信息*/
public class EventSubscriber implements Runnable {/*** 业务监听器**/private BizEventListener bizEventListener;/*** 业务事件*/private BizEvent bizEvent;/*** @param bizEventListener 事件监听者* @param bizEvent         事件*/public EventSubscriber(BizEventListener bizEventListener, BizEvent bizEvent) {super();this.bizEventListener = bizEventListener;this.bizEvent = bizEvent;}@Overridepublic void run() {bizEventListener.onEvent(bizEvent);}
}

2. 其他组件

业务事件监听器：BizEventListener.java

package com.example.event.config;import java.util.EventListener;/*** 业务事件监听器**/
public interface BizEventListener extends EventListener {/*** 是否执行事件** @param event 事件* @return*/public boolean decide(BizEvent event);/*** 执行事件** @param event 事件*/public void onEvent(BizEvent event);
}

事件引擎topic：EventEngineTopic.java

package com.example.event.config;/*** 事件引擎topic，用于区分事件类型*/
public class EventEngineTopic {/*** 入会员群*/public static final String JOIN_MEMBERSHIP_GROUP = "joinMembershipGroup";/*** 发优惠券*/public static final String ISSUE_COUPONS = "issueCoupons";/*** 推送消息*/public static final String SEND_WELCOME_MSG = "sendWelcomeMsg";}

3. 监听器实现

优惠券处理器：CouponsHandlerListener.java

package com.example.event.listener;import com.example.event.config.BizEvent;
import com.example.event.config.BizEventListener;
import org.springframework.stereotype.Component;/*** 优惠券处理器*/
@Component
public class CouponsHandlerListener implements BizEventListener {@Overridepublic boolean decide(BizEvent event) {return true;}@Overridepublic void onEvent(BizEvent event) {System.out.println("优惠券处理器:十折优惠券已发放");}
}

会员群处理器：MembershipHandlerListener.java

package com.example.event.listener;import com.example.event.config.BizEvent;
import com.example.event.config.BizEventListener;
import org.springframework.stereotype.Component;/*** 会员群处理器*/
@Component
public class MembershipHandlerListener implements BizEventListener {@Overridepublic boolean decide(BizEvent event) {return true;}@Overridepublic void onEvent(BizEvent event) {System.out.println("会员群处理器:您已成功加入会员群");}
}

消息推送处理器：MsgHandlerListener.java

package com.example.event.listener;import com.example.event.config.BizEvent;
import com.example.event.config.BizEventListener;
import org.springframework.stereotype.Component;/*** 消息推送处理器*/
@Component
public class MsgHandlerListener implements BizEventListener {@Overridepublic boolean decide(BizEvent event) {return true;}@Overridepublic void onEvent(BizEvent event) {System.out.println("消息推送处理器:欢迎成为会员！！！");}
}

事件驱动引擎配置：EventEngineConfig.java

package com.example.event.listener;import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Executor;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;import com.example.event.config.BizEventListener;
import com.example.event.config.EventEngine;
import com.example.event.config.EventEngineImpl;
import com.example.event.config.EventEngineTopic;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.concurrent.CustomizableThreadFactory;/*** 事件驱动引擎配置*/
@Configuration
public class EventEngineConfig {/*** 线程池异步处理事件*/private static final Executor EXECUTOR = new ThreadPoolExecutor(20, 50, 10, TimeUnit.MINUTES,new LinkedBlockingQueue(500), new CustomizableThreadFactory("EVENT_ENGINE_POOL"));@Bean("eventEngineJob")public EventEngine initJobEngine(CouponsHandlerListener couponsHandlerListener,MembershipHandlerListener membershipHandlerListener,MsgHandlerListener msgHandlerListener) {Map> bizEvenListenerMap = new HashMap<>();//注册优惠券事件bizEvenListenerMap.put(EventEngineTopic.ISSUE_COUPONS, Arrays.asList(couponsHandlerListener));//注册会员群事件bizEvenListenerMap.put(EventEngineTopic.JOIN_MEMBERSHIP_GROUP, Arrays.asList(membershipHandlerListener));//注册消息推送事件bizEvenListenerMap.put(EventEngineTopic.SEND_WELCOME_MSG, Arrays.asList(msgHandlerListener));EventEngineImpl eventEngine = new EventEngineImpl();eventEngine.setBizSubscribers(bizEvenListenerMap);eventEngine.setAsync(true);eventEngine.setBizListenerExecutor(EXECUTOR);return eventEngine;}
}

4. 测试类

TestController.java

package com.example.event.controller;import java.util.HashMap;
import java.util.Map;
import java.util.UUID;import javax.annotation.Resource;import com.example.event.config.BizEvent;
import com.example.event.config.EventEngine;
import com.example.event.config.EventEngineTopic;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;/*** 测试*/
@RestController
@RequestMapping("/test")
public class TestController {@Resource(name = "eventEngineJob")private EventEngine eventEngine;@GetMapping("/doRegisterVip")public String doRegisterVip(@RequestParam(required = true) String userName,@RequestParam(required = true) Integer age) {Map paramMap = new HashMap<>(16);paramMap.put("userName", userName);paramMap.put("age", age);//1、注册会员，这里不实现了System.out.println("注册会员成功");//2、入会员群eventEngine.publishEvent(new BizEvent(EventEngineTopic.JOIN_MEMBERSHIP_GROUP, UUID.randomUUID().toString(), paramMap));//3、发优惠券eventEngine.publishEvent(new BizEvent(EventEngineTopic.ISSUE_COUPONS, UUID.randomUUID().toString(), paramMap));//4、推送消息eventEngine.publishEvent(new BizEvent(EventEngineTopic.SEND_WELCOME_MSG, UUID.randomUUID().toString(), paramMap));return "注册会员成功";}
}

项目代码结构

调用接口

http://localhost:8080/test/doRegisterVip?userName=zhangsan&age=28