A few weeks ago I blogged about Spring and EJB integration, but something just did not sit well with me. Why would you want to do this at all?
I like Spring. Its myriad components make my life simpler. I can write the business code I need to faster without worrying as much about the plumbing aspects. The Spring contributors have put a lot of thought into reducing the lines of code that I as an application developer need to write. Brilliant! My stuff can be easily tested by applying DI principles and this makes me happy as it takes less effort to make the end client happy.
I have access to all of the services on the JEE platform, including transactions, naming and management and can use it as is appropriate to the task at hand. EJB is also a way of doing the same thing. If two things do the same thing, then why would you want to use them both?
I have read a lot of opinions on this question (actually, most have been on which is better, which is meaningless in this context), and have come to the conclusion that I don’t. The problem space is such that you get no additional benefits in tying the two together.
Spring is a platform, an over-arching container, a way of structuring applications and a tool set. EJB is a component model for developing the business tier that ties in directly into your JEE server. Where they cross over is that they allow your application to access the underlying services in such a way that you don’t deal with them when you write your business code.
You would use Spring to manage your business tier when you want to write a Spring application – ORM templates, Webflow, Web services, Remoting API. You would use EJB when you want to write something like a Seam application – JSF, tying in directly to a business tier that manages your persistence, jBPM for process management etc.
The question is what Style of application are you building – is it multi-tier with clear delineation of function (web tier, business tier, data access tier, anemic model), which is what Spring excels at, or do you want a tighter relationship between your tiers with a framework that manages everything in a much more integrated way (not saying that you can’t achieve this with Spring).
This is what I would term a soft decision – it’s less about technical merit and more about the vibe. Where software design meets gut feel.
Sticking EJB into a Spring app is clunky. It does not sit well. Even the stuff that you may have considered EJB for in that past have equivalents in this new world. Remoting (largely out of favour in preference to WS), listening on the end of JMS queues (which I like MDBs for) have nicer corresponding elements that sit better in Spring.
The application style is up to you at the end of the day. Whether you like the full prescribed JEE stack using EJB, or mix and matching the frameworks that you are productive in with Spring, run with it. Just keep in mind the problems that each piece of your application is trying to solve, and don’t double up. It will only make your applications unnecessarily complex.
As a side note, my current project has dropped EJB3 from the rest of the (Spring) stack.