Java Enterprise in a Nutshell, Second Edition

Chapter 8. Enterprise JavaBeans (EJB)

The introduction of RMI and JavaBeans to the core Java APIs brought a standard distributed object framework and a component model to Java. The Enterprise JavaBeans (EJB^[33]) architecture builds on these foundations to provide a standard distributed component model.

So, you may ask, how are EJB components different from regular distributed objects built using RMI or local (nondistributed) components defined using the JavaBeans component model? Well, they aren’t, in a sense. An EJB component has the remote capabilities of an RMI or CORBA object, in the sense that it can be exported as a remote object using RMI or RMI/IIOP. An EJB component is also a JavaBeans component, since it has properties that can be introspected, and it uses JavaBeans conventions for defining accessor methods for its properties. An EJB is much more than the sum of these parts, however. The EJB architecture provides a framework in which the enterprise bean developer can easily take advantage of transaction processing, security, persistence, and resource-pooling facilities provided by an EJB environment. These facilities don’t come for free, of course. You need to understand how they work and what rules your EJB object needs to follow in order to take advantage of these services.

Enterprise JavaBeans are useful in any situation where regular distributed objects are useful. They excel, however, in situations that take advantage of the component nature of EJB objects and ...