Execution Order of @PostConstruct

Question

I have 2 singletons in my JEE application that I want to initialize at start up. Something like this:

@Singleton
@Startup
public class ServiceB {

    @EJB
    private ServiceA a;

    @PostConstruct
    private void init() {
        ....
    }
}

ServiceB doesn't really need ServiceA, I just added the dependency to make sure that ServiceA is fully initialized (read: @PostConstruct-method finished) before ServiceB's init() -Method starts.

But it doesn't wait. ServiceB actually starts before ServiceA.

Is there any way to ensure that one Bean's @PostConstruct- method waits for another Bean's @PostConstruct-method to finish?

I know I could just remove the @PostConstruct Annotation in ServiceA and call it directly from ServiceB

    @PostConstruct init() {
        a.init();
    }

but I have deployments where there is no ServiceB. So I can't rely on ServiceB to init ServiceA. ServiceA has to do that itself. And ServiceB must wait for ServiceA to be done with it.

Answer 1

Use the @DependsOn annotation to declare an initialization dependency on startup beans.

Example:

@Singleton
@Startup
public class ServiceA {
    @PostConstruct
    public void init() { ... }
}

@Singleton
@Startup
@DependsOn("ServiceA")
public class ServiceB {
    @EJB
    ServiceA a;

    @PostConstruct
    public void init() { ... } // will be called after a is initialized
}