EJB runtime context, dependency injection, and crosscutting logic - EJB 3 in Action - page 189

5.2.14. EJB versus CDI injection
The @EJB annotation is a fast, easy, and powerful way to have the EE server inject EJBs
into managed resources for you. The @EJB annotation was a great step forward for simpli-
fying Enterprise development and introducing DI to the EJB container. But @EJB is lim-
ited to injecting only EJBs and only into managed resources like other EJBs, JSF-backing
beans, and Servlets. CDI, on the other hand, is much more powerful and @Inject can in-
ject just about anything into anything else. This includes the ability for @Inject to inject
EJBs. Because @Inject is more powerful and can inject EJBs, why use @EJB ?
For simple cases, @EJB and @Inject are interchangeable. Suppose ActionBazaar's
SimpleBidService is a stateless no-interface EJB, which is as simple as you can get:
@Stateless
public class SimpleBidService {
...
}
In this case, @EJB and @Inject can be used exactly the same way and produce exactly
the same results:
@Inject
SimpleBidService bidService;
@EJB
SimpleBidService bidService;
But anything beyond this simple example and CDI starts to have a few problems. For ex-
ample, suppose BidService becomes an interface with multiple implementations:
public interface BidService { ... }
@Stateless(name="defaultBids")
public class DefaultBidService implements BidService { ... }
@Stateless(name="clearanceBids")
public class ClearanceBidService implements BidService { ... }
@EJB handles this nicely in a few ways, but the easiest is to use the beanName parameter:
@EJB(beanName="clearanceBids")
BidService clearanceBidService;