JBoss AOP is a 100% Pure Java Aspected Oriented Framework usable in any programming environment or tightly integrated with our application server. Aspects allow you to more easily modularize your code base when regular object oriented programming just doesn't fit the bill. It can provide a cleaner separation from application logic and system code. It provides a great way to expose integration points into your software. Combined with JDK 1.5 Annotations, it also is a great way to expand the Java language in a clean pluggable way rather than using annotations solely for code generation.

JBoss AOP is not only a framework, but also a prepackaged set of aspects that are applied via annotations, pointcut expressions, or dynamically at runtime. Some of these include caching, asynchronous communication, transactions, security, remoting, and many many more.

An aspect is a common feature that's typically scattered across methods, classes, object hierarchies, or even entire object models. It is behavior that looks and smells like it should have structure, but you can't find a way to express this structure in code with traditional object-oriented techniques.

For example, metrics is one common aspect. To generate useful logs from your application, you have to (often liberally) sprinkle informative messages throughout your code. However, metrics is something that your class or object model really shouldn't be concerned about. After all, metrics is irrelevant to your actual application: it doesn't represent a customer or an account, and it doesn't realize a business rule. It's simply orthogonal.