Spring Framework Event Handling

External

• https://www.baeldung.com/spring-events

Internal

• Spring Framework
• Spring Dependency Injection and Inversion of Control Container Concepts

TO PROCESS

• https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-spring-application.html#boot-features-application-events-and-listeners

Overview

One of application context's capabilities is to handle events. The events are by default synchronous, which has a few advantages, one of them being the fact that the listener is able to participated in the publisher's transaction context.

Threading Consideration

Spring event handling is single threaded and synchronous in nature. If an event is published, until and unless all receivers get the message, the processes are blocked and the flow will not continue.

Event

Events are instances extending ApplicationEvent.

Standard Events

• ContextStartedEvent
• ContextStoppedEvent

Publisher

Events can be published using publishers. Any custom publisher should inject an ApplicationEventPublisher object.

package org.springframework.context;

@FunctionalInterface
public interface ApplicationEventPublisher {
  default void publishEvent(ApplicationEvent event) {
    publishEvent((Object) event);
  }
  void publishEvent(Object event);
}

Events can be published directly in the application context:

Application Event Listener

Listeners should implement the ApplicationListener interface.

Adding Application Listeners

applicationContext.addApplicationListener(...);