Spring Boot的消息事件机制

Spring Boot自带了消息机制，能够让咱们在一个地方发布消息，多个地方同时接收消息并处理消息，固然这是在同一个JVM内存下进行的，不一样的进程还须要使用MQ来实现。我以为该消息模式跟观察者模式有必定的区别，观察者模式通常观察的是一个对象内部属性发生变化的时候使用。而该消息机制能够在任意地方使用。

消息事件自己是一个对象，继承于ApplicationEvent

@Data
public class DemoEvent extends ApplicationEvent {
    private String type;
    private List<Map> msg;

    public DemoEvent(Object source,String type,List<Map> msg) {
        super(source);
        this.type = type;
        this.msg = msg;
    }
}

还须要有一个消息事件发布者，将这个消息事件给发布出去

@Component
public class DemoPublisher {
    @Autowired
    ApplicationContext applicationContext;

    public void publish(DemoEvent demoEvent) {
        applicationContext.publishEvent(demoEvent);
    }
}

而后就是咱们的侦听者，侦听者能够有任意个根据业务不一样作不一样的处理，他的写法分两种，一个是实现了ApplicationListener接口，一个是在方法上打上@EventListener标签

@Component
@Slf4j
public class DemoListener implements ApplicationListener<DemoEvent> {
    @Override
    @Async
    public void onApplicationEvent(DemoEvent demoEvent) {
        log.info("接收到publisher发送到消息，时间" + Time.getTime());
        List<Map> msg = demoEvent.getMsg();
        String type = demoEvent.getType();
        try {
            Thread.sleep(3000);
        }catch (Exception e) {
            e.printStackTrace();
        }
        log.info("类型" + type + ",消息内容:" + msg);
    }
}

@Component
@Slf4j
public class DemoListener1 {
    @EventListener
    public void onDemoEvent(DemoEvent demoEvent) {
        log.info("listener1经过注解接收到了publisher发送的消息，时间" + Time.getTime());
        String type = demoEvent.getType();
        List<Map> msg = demoEvent.getMsg();
        try {
            Thread.sleep(2000);
        }catch (Exception e) {
            e.printStackTrace();
        }
        log.info("listener1:类型" + type + ",消息内容：" + msg);
    }
}

可是咱们须要知道的是，多个消息监听是同步执行的，他们会发生阻塞，因此咱们须要进行异步监听，实现异步监听只须要在方法上打上@Async标签，同时在Springboot主程序中开启容许异步

@EnableAsync
@SpringBootApplication
public class LanmdaApplication {

   public static void main(String[] args) {
      SpringApplication.run(LanmdaApplication.class, args);
   }

}

最后写一个测试的Controller

@Slf4j
@RestController
public class TestController {
    @Autowired
    private DemoPublisher publisher;

    @GetMapping("/test")
    public String testListener() {
        List<Map> list = new ArrayList<>();
        Map<String,String> m1 = new HashMap<>();
        m1.put("1","2");
        Map<String,String> m2 = new HashMap<>();
        m2.put("3","4");
        Map<String,String> m3 = new HashMap<>();
        m3.put("5","6");
        list.add(m1);
        list.add(m2);
        list.add(m3);
        log.info("开始发布消息:" + Time.getTime());
        publisher.publish(new DemoEvent(this,"测试消息",list));
        log.info("消息发布结束:" + Time.getTime());
        return "消息发布成功";
    }
}

执行后，日志以下

2019-07-21 10:42:39.686  INFO 1756 --- [nio-8080-exec-1] c.g.lanmda.controller.TestController     : 开始发布消息:10:42:39
2019-07-21 10:42:39.687  INFO 1756 --- [nio-8080-exec-1] com.guanjian.lanmda.event.DemoListener1  : listener1经过注解接收到了publisher发送的消息，时间10:42:39
2019-07-21 10:42:41.690  INFO 1756 --- [nio-8080-exec-1] com.guanjian.lanmda.event.DemoListener1  : listener1:类型测试消息,消息内容：[{1=2}, {3=4}, {5=6}]
2019-07-21 10:42:41.695  INFO 1756 --- [nio-8080-exec-1] .s.a.AnnotationAsyncExecutionInterceptor : No task executor bean found for async processing: no bean of type TaskExecutor and no bean named 'taskExecutor' either
2019-07-21 10:42:41.697  INFO 1756 --- [nio-8080-exec-1] c.g.lanmda.controller.TestController     : 消息发布结束:10:42:41
2019-07-21 10:42:41.697  INFO 1756 --- [cTaskExecutor-1] com.guanjian.lanmda.event.DemoListener   : 接收到publisher发送到消息，时间10:42:41
2019-07-21 10:42:44.701  INFO 1756 --- [cTaskExecutor-1] com.guanjian.lanmda.event.DemoListener   : 类型测试消息,消息内容:[{1=2}, {3=4}, {5=6}]