Dependency Injection EJB 3 - too many choices?
If you need method level transaction management, security, concurrency management or any other services that a session bean can offer then make them EJB session beans. You can start out with managed beans and then make them session beans as and when you need to.
If you want to inject these session beans into managed beans (which in CDI is anything in a jar file that contains a beans.xml file in the meta-inf directory) then use @EJB. If you want to inject a plain managed bean into a session bean use @Inject.
If you want to inject remote session beans (or any Java EE remote resource) then this link explains how you can do this via an adapter class. Essentially it keeps all of your nasty strings for lookups etc in one place and allows you then to treat these remote resources just like any other injectable bean (via the @Produces annotation on the adapter member variables). You don't have to do this but it is recommended.
I would definitely vote against mixing frameworks.
I'm working on a project that is hooked on EJB, Spring and JBoss Seam (and also has half-Flex, half-JSF front-end). A true technology zoo!
Anyway, wiring it all together is not the worst part, those frameworks have flexible injection capabilities. Testing is also more or less bearable.
The most painful was to get rid of memory leaks caused by different lifecylce models, synchronize transaction, and clean up threading behavior.
Now we're moving to pure Java EE 6 (getting rid of Spring, Flex and shifting from Seam to CDI). So far we're really pleased with the results.BTW, I'm not criticizing Spring. Stick with either Java EE or Spring stack, mixing them is just asking for trouble.
Well in general in Java there are "too many choices," so certainly in this area as well. I would not describe EJB as a general purpose Dependency Injection framework, rather they use DI for their purposes. If that is how you want to code, you should look to add a framework for this purpose. If you know and like Spring, go for it. I have used Guice with EJB's (here is a nice cookbook) to good effect as well, if you needed yet another framework to figure out how to do this.