EventListener使Spring创建所有作用域bean

Question

I have session scoped beans and want them to listen to events. For example

@Component
@VaadinSessionScope
public class MyView {

    @EventListener
    public void onSearch(SearchEvent event) {
    }
}

The problem is if I add the @EventListener annotation all session scoped beans that are event listeners are created.

Is there a way to prevent creating beans and only send the event to already exisiting beans or can I register event handlers programmatically?

Answer 1

I decided to go for a programmatic event handler registration.

You need the ApplicationEventMulticaster that you can inject:

@Autowired 
ApplicationEventMulticaster applicationEventMulticaster;

Then I hold a reference to a dynamically created EventListener :

private ApplicationListener<ApplicationEvent> applicationEventApplicationListener;

It's important to note that the class must not implement the ApplicationListener interface. That's the same as annotating a method with @EventListener and will leed to the unwanted bean creation.

private ApplicationListener<ApplicationEvent> createApplicationEventApplicationListener() {
     return event -> onApplicationEvent(event);
}

In my case when the component becomes visible I add the listener and when it's not visible I remove the listener:

if (visible) {
    if (applicationEventApplicationListener == null) {
        applicationEventApplicationListener = createApplicationEventApplicationListener();
    }
    applicationEventMulticaster.addApplicationListener(applicationEventApplicationListener);
} else {
    if (applicationEventApplicationListener != null) {
           applicationEventMulticaster.removeApplicationListener(applicationEventApplicationListener);
    }
}

That finally worked for me.