applicationListener

https://blog.csdn.net/ilovejava_2010/article/details/7953419

1.自定义类继承ApplicationEvent,给自定义事件加上相应的操作，

2.然后ApplicationContext对象观察到事件后，context.publishEvent(event);传递给实现该事件的监听器类，implements ApplicationListener .

二次调用问题

https://blog.csdn.net/wo541075754/article/details/71720984/

https://blog.csdn.net/wangyang1354/article/details/50759778  重复调用问题

if(contextRefreshedEvent.getApplicationContext().getParent() != null){
            return;
}

1. if(event instanceof MessageEvent){

2. MessageEvent messageEvent = (MessageEvent) event;

3. System.out.println("信息内容是:" + messageEvent.getMessageContent());

4. }