基于Spring事件驱动模式实现业务解耦

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<String, List<BizEventListener>> bizSubscribers = new HashMap<>(16);

    @Override
    public void publishEvent(BizEvent event) {
        List<BizEventListener> 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 <tt>bizListenerExecutor</tt>.
     *
     * @param bizListenerExecutor value to be assigned to property bizListenerExecutor
     */
    public void setBizListenerExecutor(Executor bizListenerExecutor) {
        this.bizListenerExecutor = bizListenerExecutor;
    }

    /**
     * Setter method for property <tt>bizSubscribers</tt>.
     *
     * @param bizSubscribers value to be assigned to property bizSubscribers
     */
    public void setBizSubscribers(Map<String, List<BizEventListener>> bizSubscribers) {
        this.bizSubscribers = bizSubscribers;
    }

    /**
     * Setter method for property <tt>async</tt>.
     *
     * @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 <tt>topic</tt>.
     *
     * @return property value of topic
     */
    public String getTopic() {
        return topic;
    }

    /**
     * Getter method for property <tt>id</tt>.
     *
     * @return property value of id
     */
    public String getBizId() {
        return bizId;
    }

    /**
     * Getter method for property <tt>data</tt>.
     *
     * @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;
    }

    @Override
    public 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 {

    @Override
    public boolean decide(BizEvent event) {
        return true;
    }

    @Override
    public 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 {
    @Override
    public boolean decide(BizEvent event) {
        return true;
    }

    @Override
    public 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 {

    @Override
    public boolean decide(BizEvent event) {
        return true;
    }

    @Override
    public 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<String, List<BizEventListener>> 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<String, Object> 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