Spring refresh: Custom Event listeners

You can also create your own listeners in Spring. For example whenever a new role is added to the system, you would want to publish a custom event and have a custom listener listent to this and say log them (or) send an email.

Steps to do this.
1. Create a custom event.
2. Create a custom  event listener handling that event.
3. Trigger (or) publish the event when something happens.


1. Create a custom event.

public class UserEvent extends ApplicationEvent {

    private AppRole appRole;

    public UserEvent(Object source, AppRole appRole) {
        super(source);
        this.appRole = appRole;
    }

    public AppRole getAppRole() {
        return appRole;
    }
}

2. Create a custom  event listener handling that event.

@Componentpublic class UserEventListener {
    Logger logger = Logger.getLogger(UserEventListener.class);

    @EventListener    public void handleAppRoleListener(UserEvent userEvent) {
        logger.info("User event listener: " + userEvent.getAppRole().getName());
    }
}

3. Trigger (or) publish the event when something happens.

@Autowiredprivate ApplicationEventPublisher applicationEventPublisher;

@Transactionalpublic AppRole save(@RequestBody AppRole appAppRole) {
    roleRepository.save(appAppRole);
    logger.info("App role info modified : " + appAppRole);    applicationEventPublisher.publishEvent(new UserEvent(this, appAppRole));    return appAppRole;
}

Thats it. Now whenever a new role is added, you will get a message in the console as below.

2018-02-24 01:11:54.375  INFO 51885 --- [nio-8080-exec-1] cs.trk.user.util.UserEventListener       : User event listener: User

2018-02-24 01:11:54.433  INFO 51885 --- [nio-8080-exec-1] cs.trk.user.util.AppListener             : -- Request Handled at : Sat Feb 24 01:11:54 CST 2018

Create a custom event :-)