Since the Enterprise JavaBean (EJB) 2.0 specification came out, I have not hesitated to recommend that developers use all the forms of EJBs -- in the proper context, of course. These forms include sessions (stateless and stateful), entities, and message driven beans (MDBs). The trouble is that two years later, many Java developers have not evolved their thinking along with the specification, and much misinformation is still being spread regarding when various types of EJBs are best used (or not used).
Many now believe that Service Oriented Architectures (SOAs) and Service Data Objects (SDOs) have eliminated the need for EJBs, concluding that there is no real need to evolve their thinking. Nothing could be farther from the truth. In fact, EJBs play a central role in the implementation of both -- especially if your preferred programming language is Java.
To address this situation, we have created The EJB Advocate, a new recurring column taking the point of view of someone who has no reservations about recommending EJBs under the right circumstances, and will be written in the style of an advice column -- except that each column will consist of the back-and-forth dialogue with a single "questioner" in the course of recommending a solution to an interesting design issue (instead of a brief treatment of many questions).
This approach simulates the flow of a typical consulting session, where an issue presented by a "client" usually leads to one or more questions by the "consultant" -- The EJB Advocate. The answers to those questions lead to a proposed solution, which may lead to other related issues that impact the final recommended solution. By the end, you should get a pretty good idea of some aspects to consider when choosing the right EJB for the job. You should also get a feel for why The EJB Advocate believes that: There are no bad patterns, only bad applications of patterns.
First up, The EJB Advocate explores the design issue of functional decomposition and how session EJBs can be used to solve this problem. In the end, you should have some insights into when remote and local interfaces to stateless and stateful session implementations could apply.
Read this month's column now.
- Java 2 Platform, Enterprise Edition (J2EE) specification, the definitive source
- Enterprise Java Programming with IBM WebSphere, Second Edition, by Kyle Brown, Gary Craig, Greg Hester, Russell Stinehour, W. David Pitt, Mark Weitzel, JimAmsden, Peter M. Jakab, Daniel Berg. Foreword by Martin Fowler.
Geoff Hambrick is a lead consultant with the IBM Software Services for WebSphere Enablement Team and lives in Round Rock, Texas (near to Austin). The Enablement Team generally helps support the pre-sales process through deep technical briefings and short term Proof of Concept engagements. Geoff was appointed an IBM Distinguished Engineer in March of 2004 for his work in creating and disseminating best practices for developing J2EE applications hosted on IBM WebSphere Application Server.