Are CDI event observer methods compatible with EJBs?

Question

I have a Singleton EJB (javax.ejb.Singleton version. sigh.) which has a CDI observer method on it. When I try to deploy this to glassfish 3.1 the server fails to deploy the EAR file without any real explanation - simply saying there was an exception during deployment without any more details.

SEVERE: Exception while loading the app
SEVERE: Exception while shutting down application container
....
SEVERE: Exception while shutting down application container : java.lang.NullPointerException

This is the CDI event listener :

public void updateFromGranule(@Observes @CloudMask GranuleAvailableEvent granuleEvent) {
    LOG.info("updating cloud map");
    update(granuleEvent.getGranule(), CloudMask.class);
    fireUpdate();
}

If I change the Singleton bean to just be an @ApplicationScoped bean the app deploys fine. Similarly, if I remove the CDI event observer method the application deploys fine. I actually need the class to be an EJB singleton because I want the transaction, thread safety etc. of EJBs, so just leaving this as a @ApplicationScoped POJO isn't much use to me. The problem doesn't seem to be limited to Singleton beans though - I've experimented by changing the annotation to @Stateless and @Stateful and I get the same issue.

It seems to me that this might be a bug in Weld, perhaps Weld and EJB are fighting about how they proxy that method - presumably EJB needs to add an interceptor class and wrap that method to ensure thread safety, and Weld is trying to do something else to make the event listener work?

Am I misunderstanding something here, and should CDI event handlers simply not be used on EJBs (in which case there should be better error messages from glassfish) - or is this actually just a bug in the CDI or EJB implementation?

jportway jportway · Accepted Answer · 2011-05-15T21:07:44

I think this is the answer :

CDI observer methods must apparently either be static or declared in the local interface of an EJB if the EJB declares a local interface. Normally if you try to declare an observer method that isn't in the local interface you get an exception from Weld like this :

org.jboss.weld.exceptions.DefinitionException: WELD-000088 Observer method must be static or local business method:  [method] public org.stain.ObserverBean.testMethod(EventClass) on public@Singleton class org.stain.ObserverBean

For some reason glassfish does not report this exception properly when loading my EAR file and simply says Exception while loading the app.

Adding the method to the local interface (or removing the interface declaration on the class) fixes the problem and allows the application to load normally.

Are CDI event observer methods compatible with EJBs?

2 Answers