Scoped Spring events possible?

Question

The Spring event mechanism supports publishing application events and listening to these events within Spring components via the @EventListener annotation. However, I cannot find anything about sending events within a specific scope in the documentation. My specific need for Vaadin is:

• in context of a user interaction, send an event (e.g. logged-in event)
• this event should only be consumed by beans in same @UIScope, i.e. other user UIs shouldn't be effected

Is that possible? NOTE: This is not really specific to Vaadin. I could also ask how it would be done with Spring web mvc request scope.

Answer 1

TL;DR : I think it already works as you wanted it

Long version :

The documentation is somewhat unclear about this, but having tried a simple test :

A controller that publishes events :

@Controller
public class FooController {
    @Autowired
    private ApplicationEventPublisher publisher;

    @GetMapping("/fireEvent")
    public void fireEvent() {
        publisher.publishEvent(new FooEvent(this));
    }
}

And a scoped bean that listens :

@Scope(value = WebApplicationContext.SCOPE_REQUEST)
@Component
public class FooListener {
    @EventListener(FooEvent.class)
    public void listen() {
         System.out.println("I'm listening. PS : I am "+this.toString());
    }
}

And when running two concurrent requests, only the listener scoped to the the same httprequest gets the event.

---

My interpretation (without having looked at it really deeply, so take it with a grain of salt) :

It seems to me that the ApplicationEventMulticaster's ListenerRetriever uses the BeanFactory to get the beans that were previously registered as listeners (by their names). And obviously, the factory will return a bean in the current scope.

Answer 2

Please see if this is what you are looking for:

Main application :

   package com.fg7.evision.EventList;

    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    import org.springframework.context.annotation.ComponentScan;

    @ComponentScan(basePackages = "com.fg7.evision.EventList")
    public class EventApplication {


        public static void main(String[] args) {
           MyScopedEvent event = new MyScopedEvent("hello world");
           AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(EventApplication.class);
            ctx.publishEvent(event);
        }

    }

Event :

 package com.fg7.evision.EventList;

    public class MyScopedEvent  {

        private String message;

        public MyScopedEvent( String message) {
            this.message = message;
        }

        public String getMessage() {
            return message;
        }
    }

Event listener scoped to Singleton scope only.

package com.fg7.evision.EventList;

import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component(value = "listener")
public class ScopedEventListener implements BeanNameAware {

    @Autowired
    ConfigurableApplicationContext context;

    String beanName;

    @Override
    public void setBeanName(String name) {
        this.beanName = name;
    }

    @EventListener(condition = "@listener.getScope() == 'singleton'")
    public void handleEvent(MyScopedEvent myScopedEvent) {
        System.out.println(myScopedEvent.getMessage());

    }

    public String getScope(){
        return this.context.getBeanFactory().getBeanDefinition(this.beanName).getScope();
    }


}