ApplicationEventPublisher event what does it do?

It allows you to publish events that can be received by listenersconfigured for it.

You can use the events published by the framework or custom, to launch your own events you need 4 parts:

Setting

Declare the publisher in the web.xml so that it can publish events in the context of the application.

<listener>
    <listener-class>org.springframework.security.web.session.HttpSessionEventPublisher</listener-class>
</listener>

Event

Class to inherit from ApplicationEvent, in your case CreateParticipantEvent. For example:

public class CreateParticipantEvent extends ApplicationEvent {

  private Object conversation;
  private Object participant;

  public CreateParticipantEventextends (Object conversation, Object participant) {

    super();
    this.conversation = conversation;
    this.participant= participant;
  }

  //GETTERS, TOSTRING...

}

You can also use existing events, such as HttpSessionDestroyedEvent.

publisher

The one in charge of "firing" those events, in this case the origin of your question. For example:

public class CreateParticipantEventPublisher {

  @Autowired
  private ApplicationEventPublisher publisher;

  public Notify(Object conversation, Object participant) {

    eventPublisher.publish(new CreateParticipantEvent(conversation, participant));

  }

}

listening

The one in charge of listening to certain events. For example,

public class CreateParticipantEventListener implements ApplicationListener<CreateParticipantEvent > {


  @Override
  public void onApplicationEvent(CreateParticipantEvent event) {

    System.out.println("Fired event: " + event);

  }

}

To use the existing ones, you simply have to create a listenerfor them.

As additional information, here is a resource (in English) with a guide to good practices for publishing events.