code: public static void initApplicationEventMulticaster(GenericApplicationContext context) {
          ApplicationEventMulticaster multicaster;
          ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
          if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
              multicaster =
                      beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
          } else {
              multicaster = new SmartApplicationEventMulticaster(beanFactory);
              beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, multicaster);
          }
          setApplicationEventMulticaster(context, multicaster);
  
      }
docs: 修改特定上下文的Event Multicaster的默认实现
  
  @param context 被修改的上下文