Question

Is there a way to decide what EJB implementation to use at runtime when you have more than one implementation? I can’t use annotations or deployment descriptor because the logic is not known until runtime.

Let’s say that I have the following EJBs implementations:
MyEJBFoo MyEJBBar, both implement MyEJB business interface. How can I still do dependency injection of that EJB if the implementation to use is known until runtime with let’s say a flag called DEV_MODE = TRUE/FALSE stored in a resource bundle and if it is true it must use MyEJBFoo and if it is false then MyEJBBar.

I was thinking factory pattern but I’m not sure if it is the best way to do it.

Answer 1

Use a delegating MyEJB:

public class MyEJBDelegatingImpl implements MyEJB {
    // Inject: can't remember exact annotation
    private MyEJB myEJBFoo;

    // Inject: can't remember exact annotation
    private MyEJB myEJBBar;

    private getDelegate() {
        if (condition for myEJBFoo) {
            return myEJBFoo;
        } else {
            return myEJBBar;
        }
    }

    ...
    //Now implement MyEJB delegating to getDelegate()
} 

Only caveat is that both instances (myEJBFoo and myEJBBar) have to be instantiable no matter what the environment conditions are, because you are injecting both unconditionally in the delegating MyEJB.