What is an Enterprise Java Bean really?

Question

On the Tomcat FAQ it says: "Tomcat is not an EJB server. Tomcat is not a full J2EE server."

But if I:

• use Spring to supply an application context
• annotate my entities with JPA annotations (and use Hibernate as a JPA provider)
• configure C3P0 as a connection pooling data source
• annotate my service methods with @Transactional (and use Atomikos as JTA provider)
• Use JAXB for marshalling and unmarshalling
• and possibly add my own JNDI capability

then don't I effectively have a Java EE application server? And then aren't my beans EJBs? Or is there some other defining characteristic?

What is it that a Java EE compliant app server gives you that you can't easily/readily get from Tomcat with some 3rd party subsystems?

Answer 1

EJBs are JavaEE components that conform to the javax.ejb API.

JavaEE is a collection of APIs, you don't need to use all of them.

Tomcat is a "partial" JavaEE server, in that it only implements some of the JavaEE APIs, such as Servlets and JNDI. It doesn't implement e.g. EJB and JMS, so it's not a full JavaEE implementation.

If you added some additional bits and pieces (e.g. OpenEJB, HornetQ), you'd add the missing parts, and you'd end up with a full JavaEE server. But out of the box, Tomcat isn't that, and doesn't try to be.