CDI: 2 Producers with different qualifiers

Question

I have 2 producer-methods, one has only 1 qualifier and one has 2 qualifiers, the one from the first producer and an additional one:

@ApplicationScoped
public class MyProducer {

  @Produces
  @Qualifier1
  MyBean produce1(InjectionPoint injectionPoint) {
    ...
  }

  @Produces
  @Qualifier1
  @Qualifier2
  MyBean produce2(InjectionPoint injectionPoint) {
    ...
  }
}

If I try to @Inject MyBean with both qualifiers, everything works fine, produce2 is called. But when injecting MyBean with only @Qualifier1, I get an AmbiguousResolutionException. In my opinion, produce2 should only be called when injection point has both qualifiers. Why isn't that the case and what can I do to make it work?

Unfortunately I can not change producer-method 1, because it is in a library. The basic plan is to call my own producer if the injection point has my additional qualifier and if not, call the one from the library.

Answer 1

I think the observed behavior is clearly specified in CDI 2.0, ch.2.3.4 "Specifying qualifiers of an injected field":

A bean may only be injected to an injection point if it has all the qualifiers of the injection point.

Assuming an injection point:

@Inject @Qualifier1 MyBean myBean;

Then the beans produced by both produce1 and produce1 "have all the qualifiers of the injection point", i.e. @Qualifier1, so both are eligible for injection there, resulting in the AmbiguousResolutionException.

In fact, the spec gives an example exactly as the one in the question in ch.2.3.6 "Repeating qualifiers".

---

So what can you do?

For starters, do you really need to qualify produce2 with @Qualifier1? If you have no good reason, just drop @Qualifier1 from produce2 and you are done - injection points with @Qualifier1 select MyBean from the library, injection points with @Qualifier2 select the one from your code. Your injection points cannot have both @Qualifier1 and @Qualifier2.

If you still want to inject MyBean from produce2 to injection points that have both @Qualifier1 and @Qualifier2, you can still do it [DISCLAIMER: Haven't actually tried this, it will probably need tweaking]. It's a bit more involved: You have to write a portable extension, which is not a hard thing at all. Brief implementation points:

• The producer2 must be annotated ONLY with @Qualifier2
• In you extension, observe the ProcessInjectionPoint event
• If event.getInjectionPoint().getQualifiers() contains both @Qualifier1 and @Qualifier2
  • Use event.configureInjectionPoint().qualifiers(...) to remove @Qualifier1 from the set of qualifiers.

The effect is that you remove the @Qualifier1 when it is present together with @Qualifier2 at runtime.