Java – EJB 3.1 @LocalBean vs no annotation

ejbjakarta-eejava

I understand the difference between local view, remote view and no-interface view. I just don't understand what is the difference between "no view" (no annotation) and no-interface view. And also why should I annotate my interface with @Local? What if I don't annotate the interface in at all, is there a difference?

Best Solution

The rules are (from memory):

  1. Bean has a @LocalBean annotation -> bean has a no-interface view
  2. Bean has a @Local annotation -> bean has a local view
  3. Bean has a @Remote annotation -> bean has a remote view
  4. Bean has no view annotations, but directly implements an interface which has a @Local annotation -> bean has a local view
  5. Bean has no view annotations, but directly implements an interface which has a @Remote annotation -> bean has a remote view
  6. Bean has no view annotations, but directly implements an interface which has no view annotations -> bean has a local view
  7. Bean has no view annotations, and implements no interfaces -> bean has a no-interface view

So, using @LocalBean and using no annotation at all are both ways of getting a no-interface view. If you just want a no-interface view, then the simplest thing is not to annotate. Provided you're not also implementing any interfaces.

Part of the reason @LocalBean exists to add a no-interface view to a bean which also has an interface view. I imagine the scenario uppermost in the spec authors' minds was one where you have a bean like:

@Stateless
public class UserPreferences {
    public String getPreference(String preferenceName);
    public Map<String, String> getPreferences();
}

Where you would want to expose both methods locally, but only the coarser-grained getPreferences() remotely. You can do that by declaring a remote interface with just that method, then just slapping @LocalBean on the bean class. Without it, you'd have to write a pointless local interface just to expose both methods locally.

Or, to look at it another way, the @LocalBean exists because there is such a thing as a no-interface view, and the no-annotation option exists as a handy shortcut.

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