观察者模式实际应用场景-----Spring事件机制

以下伪代码是一个保存订单的功能，并会发送短信消息：

/**
* Author heling on 2019/1/9
*/
@Service
public class OrderServiceImpl implements OrderService {

    @Override
    public void saveOrder() {
        //1.创建订单
        System.out.println("订单创建成功");
        //2.发送短信
        System.out.println("恭喜您订单创建成功！----by sms");
    }
}

现有新需求：需要加一个微信通知的功能，代码如下：

/**
* Author heling on 2019/1/9
*/
@Service
public class OrderServiceImpl implements OrderService {

    @Override
    public void saveOrder() {
        //1.创建订单
        System.out.println("订单创建成功");
        //2.发送短信
        System.out.println("恭喜您订单创建成功！----by sms");
        //新需求：微信通知
        // 3.发送微信
        System.out.println("恭喜您订单创建成功！----by wechat");
    }
}

存在问题：每次创建订单需要加新功能（如新的通知方式），则要修改原有的类，难以维护。

违背设计模式的原则

1.单一职责：订单保存功能，杂糅了消息通知这些功能

2.开闭原则：对拓展开放，对修改关闭

优化方案：使用观察者模式，使创建订单和消息通知进行分离，低耦合。可以选择消息队列，spring事件机制等，本文选择Spring事件机制。

改造开始：

1.创建事件

package com.pengshu.magicwallet.admin.test;

import org.springframework.context.ApplicationEvent;

import java.util.List;

/**
* Author heling on 2019/1/9
* 订单创建活动事件
*/
public class OrderCreateEvent extends ApplicationEvent {

    private String name;

    //消息参数
    private List<String> contentList;

    public OrderCreateEvent(Object source, String name, List<String> contentList) {
        super(source);
        this.name = name;
        this.contentList = contentList;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public List<String> getContentList() {
        return contentList;
    }
    public void setContentList(List<String> contentList) {
        this.contentList = contentList;
    }
}

2.监听器

package com.pengshu.magicwallet.admin.test;

import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

/**
* Author heling on 2019/1/9
* 短信监听器
* ApplicationListener是无序的
*/
@Component
public class SmsListener implements ApplicationListener<OrderCreateEvent> {

    @Override
    public void onApplicationEvent(OrderCreateEvent event) {
        //发送短信
        System.out.println(event.getContentList().get(0) + ",您的订单:" + event.getContentList().get(1) + "创建成功! ----by sms");

    }
}

package com.pengshu.magicwallet.admin.test;

import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

/**
* Author heling on 2019/1/9
* 微信监听器
*/
@Component
public class WechatListener implements ApplicationListener<OrderCreateEvent> {

    @Override
    public void onApplicationEvent(OrderCreateEvent event) {
        //发送微信
        System.out.println(event.getContentList().get(0) + ",您的订单:" + event.getContentList().get(1) + "创建成功! ----by wechat");

    }
}

3.事件发布

package com.pengshu.magicwallet.admin.test;

import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;
import java.util.ArrayList;

/**
* Author heling on 2019/1/9
*/
@Service
public class OrderServiceImpl implements OrderService {

    @Resource
    private ApplicationContext applicationContext;

    @Autowired
    private ApplicationEventPublisher applicationEventPublisher;

    @Override
    public void saveOrder() {
        //1.创建订单
        System.out.println("订单创建成功");
        //2.发布事件
        ArrayList<String> contentList = new ArrayList<>();
        contentList.add("heling");
        contentList.add("123456789");
        OrderCreateEvent orderCreateEvent = new OrderCreateEvent(this, "订单创建", contentList);
        applicationContext.publishEvent(orderCreateEvent);//ApplicationContext是我们的事件容器上层，我们发布事件，也可以通过此容器完成发布
        //applicationEventPublisher.publishEvent(orderCreateEvent);//也可以
        System.out.println("finished!");
    }
}

打印结果：

订单创建成功

heling,您的订单:123456789创建成功! ----by sms

heling,您的订单:123456789创建成功! ----by wechat

finished!

如何异步执行监听器？

1.springboot开启事件异步设置

package com.pengshu.magicwallet;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.PropertySource;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@SpringBootApplication
@MapperScan("com.pengshu.magicwallet.mapper")
@PropertySource("classpath:authority.properties")
@EnableTransactionManagement
@EnableAsync //开启spring事件异步设置，加@Async注解
public class MagicWalletAdminApplication {
    public static void main(String[] args) {
        SpringApplication.run(MagicWalletAdminApplication.class, args);
    }
}

2.监听器类或方法添加@Async注解

打印结果：

订单创建成功

finished!

heling,您的订单:123456789创建成功! ----by sms

heling,您的订单:123456789创建成功! ----by wechat

如何制定监听器执行顺序？

package com.pengshu.magicwallet.admin.test;

import org.springframework.context.ApplicationEvent;
import org.springframework.context.event.SmartApplicationListener;
import org.springframework.stereotype.Component;

/**
* Author heling on 2019/1/9
* 微信监听器
* SmartApplicationListener可以设置顺序等
*/
@Component
public class WechatListener implements SmartApplicationListener {

    //设置监听优先级
    @Override
    public int getOrder() {
        return 1;
    }

    //监听器智能所在之一，能够根据事件类型动态监听
    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> aClass) {
        return aClass == OrderCreateEvent.class;
    }

    //监听器智能所在之二，能够根据事件发布者类型动态监听
    @Override
    public boolean supportsSourceType(Class<?> aClass) {
        return aClass == OrderServiceImpl.class;
    }

    @Override
    public void onApplicationEvent(ApplicationEvent applicationEvent) {
        OrderCreateEvent event = (OrderCreateEvent) applicationEvent;
        //发送微信
        System.out.println(event.getContentList().get(0) + ",您的订单:" + event.getContentList().get(1) + "创建成功! ----by wechat");

    }

//    @Override
//    @Async
//    public void onApplicationEvent(OrderCreateEvent event) {
//
//        //发送微信
//        System.out.println(event.getContentList().get(0) + ",您的订单:" + event.getContentList().get(1) + "创建成功! ----by wechat");
//
//    }
}

package com.pengshu.magicwallet.admin.test;

import org.springframework.context.ApplicationEvent;
import org.springframework.context.event.SmartApplicationListener;
import org.springframework.stereotype.Component;

/**
* Author heling on 2019/1/9
* 短信监听器
*/
@Component
public class SmsListener implements SmartApplicationListener {

    @Override
    public int getOrder() {
        return 2;
    }

    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> aClass) {
        return aClass == OrderCreateEvent.class;
    }

    @Override
    public boolean supportsSourceType(Class<?> aClass) {
        return aClass == OrderServiceImpl.class;
    }

    @Override
    public void onApplicationEvent(ApplicationEvent applicationEvent) {
        OrderCreateEvent event = (OrderCreateEvent) applicationEvent;
        //发送短信
        System.out.println(event.getContentList().get(0) + ",您的订单:" + event.getContentList().get(1) + "创建成功! ----by sms");

    }

//    @Override
//    @Async
//    public void onApplicationEvent(OrderCreateEvent event) {
//
//        //发送短信
//        System.out.println(event.getContentList().get(0) + ",您的订单:" + event.getContentList().get(1) + "创建成功! ----by sms");
//
//    }
}

打印结果：

订单创建成功

heling,您的订单:123456789创建成功! ----by wechat

heling,您的订单:123456789创建成功! ----by sms

finished!

在实现了SmartApplicationListener的监听器中，我们通过重写GetOrder方法来修改不同监听器的顺序，优先级越小，则越先被调用。通过配置不同的优先级，且让监听器之间阻塞调用。我们就能实现流水线式的有序事件调用，这在实际应用场景中还是蛮有意义的