7 Years Later: Still EJBs
In 1998, a student of my school had a project with Sun about EJBs. This was the beginning of EJBs, they were not public, and there was no J2EE. At that time he found it utterly complicated, and had difficulties to understand why they made it so complicated.In 2000, I worked for a company who had built in-house most components of a today J2EE application server. For example, they had their own unified messaging system, on the JSP side, they were already using custom tags, etc.. Their problem is that they took lots of time to develop in-house, all what later became standard, and almost freely available.
Today, 7 years later, the big talk, new Java products, be it Spring, or JBoss Seam, are still all about the same ideas as in the first J2EE. Spring has the freedom to include whatever technology, but in the end, their scope closely matches J2EE scope. Service Oriented Architecture (SOA), the current buzzword, will come out relatively naturally with J2EE, session EJBs being natural candidate to expose functionalities to the outer world. JBoss (or Geronimo) architecture is fully SOA: a small kernel managing services, that are exposed for other to use.
To learn about EJBs, I still find Enterprise JavaBeans by Richard Monson-Haefel, the best book. The chapter (in the 2nd Edition of the book, not in the 4th unfortunately) where he rolls his own distributed objects system is for me a testimony on how well he wants you to understand what's behind EJBs. And if you want to better understand what's behind RMI, Java Distributed Computing (O'Reilly)
has a chapter where the author rolls his own RMI.To conclude, Sun was really clever in defining J2EE scope and branding several Java technologies as J2EE (despite the awful version naming). While the ideas were very good, the developer's life was forgotten. It was too much a pain in the a** and not flexible enough (especially the ORM side). JBoss gets it right, what people need is a way to use pieces of J2EE, without imposing too much unnecessary hurdle on development.