EJB 3.1 @LocalBean vs no annotation

ejb, jakarta-ee, java

Solution

The rules are (from memory):

- Bean has a `@LocalBean` annotation -> bean has a no-interface view

- Bean has a `@Local` annotation -> bean has a local view

- Bean has a `@Remote` annotation -> bean has a remote view

- Bean has no view annotations, but directly implements an interface which has a @Local annotation -> bean has a local view

- Bean has no view annotations, but directly implements an interface which has a @Remote annotation -> bean has a remote view

- Bean has no view annotations, but directly implements an interface which has no view annotations -> bean has a local view

- 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.

Problem

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?

Original source