Spring @EventListener support in component

[denis-anisimov]

@heruan commented on Wed Jan 03 2018

When building a PWA with Flow and Spring, I'd like my components able to react on server events using Spring's @EventListener and @TransactionalEventListener. For example:

@Route("users")
public class UserList extends Grid<User> {

    // ...

    @EventListener
    public void onNewUser(NewUserEvent event) {
        UI.getCurrent().access(getDataProvider()::refreshAll);
    }

}

At the moment it seems like @EventListener-annotated methods in @Route-annotated components are not invoked when the observed event is published.

[zach-herridge]

Is there a work around to make this work currently?

[heruan]

The problem here is that component instances are created at each page load, while event listeners are singletons. I still can't imagine how components might be also event listeners, and now I feel it could be an anti-pattern.

More than a workaround, I think it would be more correct to delegate the listener method to a singleton service (i.e. a Spring @Service bean) and "subscribe" the component to the service.

I've currently implemented this using the Java Flow (not Vaadin's Flow 🙂) API, i.e. java.util.concurrent.Flow.Publisher and java.util.concurrent.Flow.Subscriber.

[d2k2-git]

The problem here is that component instances are created at each page load, while event listeners are singletons. I still can't imagine how components might be also event listeners, and now I feel it could be an anti-pattern.

More than a workaround, I think it would be more correct to delegate the listener method to a singleton service (i.e. a Spring @Service bean) and "subscribe" the component to the service.

I've currently implemented this using the Java Flow (not Vaadin's Flow 🙂) API, i.e. java.util.concurrent.Flow.Publisher and java.util.concurrent.Flow.Subscriber.

i am currently using googles EventBus, which does the job. But it's not recommended to use by the google devs. so i was looking for a simple alternative. do you have some code examples how to implement the "Flow.Subscriber" in a vaadin route?

[petersj-ess]

Is there actually a workaround for this? It's still an issue today, what's the best practice for sending events to a view?

Seems like the Spring event listeners would be perfect to use with Vaadin

[TatuLund]

The problem here is that component instances are created at each page load, while event listeners are singletons.

@petersj-ess I think the ticket should be closed, as this is fundamentally just how Spring works. The solution is to use some EventBus instead of Spring events. Naturally use that EventBus as a proxy. I.e. listen Spring events elsewhere, and post another event to EventBus there and listen to EventBus in the view.