- Transaction management.
- Scalability – you can distribute your application across multiple machines.
- Lifecycle management.
- Security management.
- Dependency Injection.
EJB’s have been with us for a long time and have certainly evolve in the right direction. From the cumbersome EJB 2.x specification with all those interfaces, a very verbose XML definition and an over-designed Entity Beans, to a more convenient EJB 3.0 spec which uses annotations and better persistence management with the introduction of JPA (Java Persistence API). The new EJB 3.1 spec even gets simpler with no need of the Local interface and the possibility to run inside a Servlet Container.
On the other hand, we have initiatives like Spring and JBoss Seam that try to bring the benefits of the EJB’s to POJO’s. They have been very successful in this task and are being widely adopted. In fact, the reason EJB’s are getting much more simpler lies in the success of these frameworks. The idea behind them is very easy to understand: use annotations inside your POJO’s when you want the benefits of EJB’s and we will use AOP (Aspect Oriented Programming) to deliver that functionality.
They even go further and bind each object to a scope. So, for example, you may want an object to last through the duration of a request or through the whole session of the user. I will not get into the details of this powerful feature but you can read more in this post where I explain how this works in JBoss Seam.
As you can see, there are two approaches to achieve the same goal. The top-down approach is used by the JCP (Java Community Process) expert group to make EJB’s simpler and the bottom-up approach used by frameworks like Spring and JBoss Seam to empower simple POJO’s with enterprise services.
We still need the standards!
Standards are good. They allow us as developers to focus on what we have to learn, facilitates the technology selection process, promotes vendor independence and are easily accepted by the executive team in companies, among other benefits.
There have been some efforts to standardize some of the bottom-up approaches. The JSR-299 (Context and Dependency Injection) is one of these efforts leaded by the Seam group which has been approved by the JCP. With JSR-299 you could have POJO’s that behave like EJB’s with dependency injection support and scope demarcation (contexts). So the question is: do we still need EJB’s?
Well, the answer is we do. Unfortunately, the JCP group wants to keep the EJB specification and the JSR-299 group had to make the concept of component (called bean in the JSR-299) more abstract to support EJB’s. I think is confusing and not good for the Java community. While other languages are moving to the KISS (keep it simple, stupid!) principle, we are making things more confusing to developers. With JSR-299, you will be able to work with or without EJB’s. The only benefit of using EJB’s will be the clustered services and JMS but that is something that could have been added to the JSR-299 component model.
Conclusion
I don’t think it’s healthy to continue changing the EJB specification to adapt it to a new simpler model. The JCP group should really let them go, create a unified component model based on POJO’s and add it to the JSR-299. We really need to keep it that simple ;)
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