执行发布ApplicationEvent事件启动自定义异步线程池

1. 自定义线程池
   @Bean
   public ThreadPoolTaskExecutor taskExecutor() {
   ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
   taskExecutor.setAllowCoreThreadTimeOut(true);
   taskExecutor.setCorePoolSize(2);
   taskExecutor.setMaxPoolSize(20);
   taskExecutor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardOldestPolicy());
   taskExecutor.setThreadFactory(new CustomizableThreadFactory("test--springThread-pool-"));
   return taskExecutor;
   }

自定义spring只默认执行ApplicationEvent的执行器
@Bean
public SimpleApplicationEventMulticaster applicationEventMulticaster(ConfigurableListableBeanFactory beanFactory,
ThreadPoolTaskExecutor taskExecutor) {
SimpleApplicationEventMulticaster multicaster = new SimpleApplicationEventMulticaster(beanFactory);
multicaster.setTaskExecutor(taskExecutor);
return multicaster;
}

2.原理:
spring启动中，AbstractApplicationContext#refresh()中，initApplicationEventMulticaster()会初始化一个ApplicationEventMulticaster实例，如果beanFactory容器中能containLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME )
public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";
就是自定义了ApplicationEventMulticaster，那就用这个 ；如果没有，就spring自己new一个ApplicationEventMulticaster实例this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);，并把单例放到容器中。

3.执行代码的地方
applicationContext.publishEvent(event)-->abstractApplicationContext.publisEvent(event)--->getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);---->Executor executor = getTaskExecutor();,这个就是自定义的线程池