My previous two articles in this series have provided a general overview of the Java 2 Platform, Enterprise Edition (J2EE) and a more detailed look at the technologies contained within the web-tier of the J2EE platform. Using these technologies allows us to build scalable web-based interfaces for our applications but one question still remains. Where should the business logic reside? This is the subject of this article.

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Most web and enterprise Java applications can be split into three parts: a front end to talk to the user, a service layer to talk to back-end systems such as databases, and business logic in between. While it is now common practice to use frameworks for both front- and back-end requirements (e.g., Struts, Cocoon, Spring, Hibernate, JDO, and Entity Beans), there is no standard way of structuring business logic. Frameworks like EJB and Spring do this at a high level, but don't help us in organizing our code. Wouldn't it would be great if we could replace messy, tangled if...then statements with a framework that gave us the same benefits of configurability, readability, and reuse that we already enjoy in other areas? This article suggests using the Drools rules engine as a framework to solve the problem.

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