springboot事件监听器怎么使用

引导案例

下面看一个简单的案例，

@Configuration
public class SelfBusiness {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SelfBusiness.class);
        context.getBean(MyService.class).doBusiness();
        context.close();
    }
    @Component
    static class MyService {
        private static final Logger logger = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher;
        public void doBusiness (){
            logger.debug("主线业务");
            logger.debug("发送短信");
            logger.debug("发送邮件");
        }
    }

运行上面的代码，观察效果

结合输出结果，这这段代码要实现的逻辑是，在主线业务执行完成后，需要执行发短信，发邮件等操作，这样写也没毛病，但不够优雅，从后续的业务可扩展性上来讲，不够友好，如果后续主线业务执行完毕，还需再增加一个其他的审计操作，则需要新增代码逻辑，这就将主线业务和支线逻辑紧密的耦合了起来；

就是说，我们期待的效果是，主线业务根本不关心其他的业务操作，只需要完成自身的逻辑就ok了，这就需要使用到spring提供的事件监听器功能；

使用事件监听器改造过程

springboot（spring）的事件监听器使用主要有两种方式，通过实现ApplicationListener接口，另一个就是在类上添加 @EventListener 注解来实现，接下来将对这两种方式逐一说明；

一、通过实现ApplicationListener接口实现步骤

1、自定义一个事件类（对象），继承ApplicationEvent

 static class MyEvent extends ApplicationEvent {
        public MyEvent(Object source) {
            super(source);
        }
    }

可以这么理解，在代码中，可能有很多种类型的事件，不同的业务对应着不同的事件，对于某个具体的监听器来说，它只想监听A这种类型的事件；

2、自定义业务类实现ApplicationListener 接口

  
	@Data
    static class Params {
        private String id ;
        private String name;
        private String phone;
    }
	@Component
    static class SmsApplicationListener implements ApplicationListener<MyEvent> {
        private static final Logger logger = LoggerFactory.getLogger(SmsApplicationListener.class);
        @Override
        public void onApplicationEvent(MyEvent myEvent) {
            Object source = myEvent.getSource();
            try {
                Params params = objectMapper.readValue(source.toString(), Params.class);
                logger.debug("userId : {}",params.getId());
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            logger.debug("执行 sms 发短信业务");
        }
    }
    @Component
    static class EmailApplicationListener implements ApplicationListener<MyEvent> {
        private static final Logger logger = LoggerFactory.getLogger(SmsApplicationListener.class);
        @Override
        public void onApplicationEvent(MyEvent myEvent) {
            Object source = myEvent.getSource();
            logger.debug("执行 email 发邮件业务");
        }
    }

显然，这里的监听器要监听的事件类型，正是上面我们定义的MyEvent ，这样，当业务被触发的时候，就可以在onApplicationEvent中拿到传递过来的参数，从而执行发短信（发邮件）业务操作了

3、主线业务发布事件

@Component
    static class MyService {
        private static final Logger logger = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher;
        public void doBusiness (){
            Params params = new Params();
            params.setId("001");
            params.setName("xiaoma");
            params.setPhone("133******");
            logger.debug("主线业务");
            try {
                publisher.publishEvent(new MyEvent(objectMapper.writeValueAsString(params)));
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            //publisher.publishEvent(new MyEvent("MyService doBusiness()"));
            //logger.debug("发送短信");
            //logger.debug("发送邮件");
        }
    }

对主线业务来说，这时候就不再需要写发送短信或邮件逻辑了，只需要一个publisher将事件发布出去即可，如果需要传递参数，将参数一起传递过去

完整的代码

@Configuration
public class SelfBusiness {
    private static ObjectMapper objectMapper = new ObjectMapper();
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SelfBusiness.class);
        context.getBean(MyService.class).doBusiness();
        context.close();
    }
    @Data
    static class Params {
        private String id ;
        private String name;
        private String phone;
    }
    /**
     * 自定义事件对象
     */
    static class MyEvent extends ApplicationEvent {
        public MyEvent(Object source) {
            super(source);
        }
    }
    @Component
    static class MyService {
        private static final Logger logger = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher;
        public void doBusiness (){
            Params params = new Params();
            params.setId("001");
            params.setName("xiaoma");
            params.setPhone("133******");
            logger.debug("主线业务");
            try {
                publisher.publishEvent(new MyEvent(objectMapper.writeValueAsString(params)));
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            //publisher.publishEvent(new MyEvent("MyService doBusiness()"));
            //logger.debug("发送短信");
            //logger.debug("发送邮件");
        }
    }
    /**
     * 监听事件触发后要执行的业务
     */
    @Component
    static class SmsApplicationListener implements ApplicationListener {
        private static final Logger logger = LoggerFactory.getLogger(SmsApplicationListener.class);
        @Override
        public void onApplicationEvent(MyEvent myEvent) {
            Object source = myEvent.getSource();
            try {
                Params params = objectMapper.readValue(source.toString(), Params.class);
                logger.debug("userId : {}",params.getId());
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            logger.debug("执行 sms 发短信业务");
        }
    }
    @Component
    static class EmailApplicationListener implements ApplicationListener {
        private static final Logger logger = LoggerFactory.getLogger(SmsApplicationListener.class);
        @Override
        public void onApplicationEvent(MyEvent myEvent) {
            Object source = myEvent.getSource();
            logger.debug("执行 email 发邮件业务");
        }
    }
}

再次运行上面的代码，观察效果，可以看到，仍然能满足预期的效果

二、通过添加 @EventListener 注解来实现

这种方式不再需要实现ApplicationListener 接口，而是直接在监听类的方法上面添加 @EventListener注解即可，相对要简化了一些，下面直接贴出完整的代码

package com.congge.config;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.Data;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;
@Configuration
public class SelfBusiness2 {
    private static ObjectMapper objectMapper = new ObjectMapper();
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SelfBusiness2.class);
        context.getBean(MyService.class).doBusiness();
        context.close();
    }
    @Data
    static class Params {
        private String id ;
        private String name;
        private String phone;
    }
    /**
     * 自定义事件对象
     */
    static class MyEvent extends ApplicationEvent {
        public MyEvent(Object source) {
            super(source);
        }
    }
    @Component
    static class MyService {
        private static final Logger logger = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher;
        public void doBusiness (){
            Params params = new Params();
            params.setId("001");
            params.setName("xiaoma");
            params.setPhone("133******");
            logger.debug("主线业务");
            try {
                publisher.publishEvent(new MyEvent(objectMapper.writeValueAsString(params)));
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
        }
    }
    @Component
    static class SmsListenerService {
        private static final Logger logger = LoggerFactory.getLogger(SmsListenerService.class);
        @EventListener
        public void smsListener(MyEvent myEvent){
            Object source = myEvent.getSource();
            try {
                SelfBusiness2.Params params = objectMapper.readValue(source.toString(), SelfBusiness2.Params.class);
                logger.debug("userId : {}",params.getId());
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            logger.debug("执行 sms 发短信业务");
        }
    }
    @Component
    static class EmailListenerService {
        private static final Logger logger = LoggerFactory.getLogger(EmailListenerService.class);
        @EventListener
        public void emailListener(MyEvent myEvent){
            Object source = myEvent.getSource();
            try {
                SelfBusiness2.Params params = objectMapper.readValue(source.toString(), SelfBusiness2.Params.class);
                logger.debug("userId : {}",params.getId());
            } catch (JsonProcessingException e) {
                e.printStackTrace();
            }
            logger.debug("执行 email 发邮件业务");
        }
    }
}

运行上面的代码，观察效果，同样可以达到预期的效果

三、使用异步

更进一步来说，为了提升主线业务的逻辑执行效率，我们希望发布事件的业务逻辑异步执行，这个该如何做呢?

翻阅源码可以知道，ApplicationEventPublisher 默认发布事件时候采用单线程同步发送，如果需要使用异步，需要自定义 ThreadPoolTaskExecutor ，以及SimpleApplicationEventMulticaster ，因此我们只需要覆盖一下这两个组件的bean即可，在上面的业务类中将下面的这两个bean添加进去；

@Bean
    public ThreadPoolTaskExecutor executor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(100);
        return executor;
    }
    @Bean
    public SimpleApplicationEventMulticaster applicationEventMulticaster(ThreadPoolTaskExecutor executor) {
        SimpleApplicationEventMulticaster eventMulticaster = new SimpleApplicationEventMulticaster();
        eventMulticaster.setTaskExecutor(executor);
        return eventMulticaster;
    }

这时候再次运行代码，反复运行多次，就可以看到效果

对比下上面单线程效果

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