Why EJB (3+)

I have heard people mentioning, why do you need EJBs; my project is great without them. In early days, I too wasn't very convinced. What value it adds ? Can't we leave without EJBs ?

The answer to most of such questions would be; may be!

It's not that you can't implement a distributed application without EJBs. I have worked on couple of quite successful distributed applications which didn't use EJB at all. For that matter, there is no framework/technology which is must in a given situation. There are always few alternatives, but the question is what's the cost or advantages for making a particular choice?

Let's try to understand EJB and other server side Java components:

Where it fits

EJBs runs inside EJB container (of application server) for abstracting your business logic. Below diagram shows different server side components and their relationship with EJB (just shown some of them). When EJB is not there the line gets blurred and the business logic is spread across servlet and other middle layer components like JPA, JDBC, JMS etc.

Why do we need it ?

Business logic shouldn't be performed by web interface component and similarly by persistence layer as well. Web-interface should specialize in handling http request and delegating it appropriately to business component and persistence layer should focus on CRUD operations.  If your business logic is spread across multiple component, it's not easy to manage it. You are violating loose coupling and separation of concern design principles (not following MVC architectural pattern).

If your business logic is light-weight then you might go on with this approach. But are you sure, that it's going to remain light weight forever? Change is inevitable!

When you have a truly distributed application with multiple server side components and business logic is not so trivial, you will feel the need to bring in an specialized component sooner or later. EJB integrates quite easily with other server side components like JPA (for persistence services), JTA (for transaction services), JMS (for providing messaging services), JNDI (for providing directory services) etc. EJB helps scaling out your application.

Arguments given here are generic, but have written this article keeping in mind features and power of EJB 3+.  Development with EJB 3+ is quite simple - no complex configuration in XML, simple POJO class, uses annotation, and makes development quite a breeze. 

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happy learning !