java listen to ContextRefreshedEvent

Question

I have a classX in my spring application in which I want to be able to find out if all spring beans have been initialized. To do this, I am trying to listen ContextRefreshedEvent.

So far I have the following code but I am not sure if this is enough.

import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;

public classX implements ApplicationListener<ContextRefreshedEvent> {
    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
       //do something if all apps have initialised
    }
}

1. Is this approach correct to find out if all beans have initialsed?
2. What else do I need to do to be able to listen to the ContextRefreshedEvent ? DO I need to register classX somewhere in xml files ?

Answer 1

Spring >= 4.2

You can use annotation-driven event listener as below :

@Component
public class classX  {

    @EventListener
    public void handleContextRefresh(ContextRefreshedEvent event) {

    }
}

the ApplicationListener you want to register is defined in the signature of the method.

Answer 2

A ContextRefreshEvent occurs

when an ApplicationContext gets initialized or refreshed.

so you are on the right track.

What you need to do is declare a bean definition for classX.

Either with @Component and a component scan over the package it's in

@Component
public class X implements ApplicationListener<ContextRefreshedEvent> {
    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
       //do something if all apps have initialised
    }
}

or with a <bean> declaration

<bean class="some.pack.X"></bean>

Spring will detect that the bean is of type ApplicationListener and register it without any further configuration.

Later Spring version support annotation-based event listeners. The documentation states

As of Spring 4.2, you can register an event listener on any public method of a managed bean by using the @EventListener annotation.

Within the X class above, you could declare an annotated method like

@EventListener
public void onEventWithArg(ContextRefreshedEvent event) {
}

or even

@EventListener(ContextRefreshedEvent.class)
public void onEventWithout() {

}

The context will detect this method and register it as a listener for the specified event type.

The documentation goes into way more detail about the full feature set: conditional processing with SpEL expression, async listeners, etc.

---

Just FYI, Java has naming conventions for types, variables, etc. For classes, the convention is to have their names start with an uppercase alphabetic character.

Answer 3

I will prefer ApplicationReadyEvent. I found ContextRefreshedEvent is called before my http server is started. ApplicationReadyEvent will make sure your application is ready to take request.

    @EventListener(ApplicationReadyEvent.class)
    public void startApp() {
        LOGGER.info("Application is now ready!");
    }