SPRING - Aspect Oriented Programming

Before going through a sample on how to use Aspect Oriented Programming or AOP, it will be helpful to go through the basics on the AOP Concepts.

Aspect: A modularization of a concern that cuts across multiple classes. Transaction management is a good example of a crosscutting concern in J2EE applications. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (the @AspectJ style).

Join point: A point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.

Pointcut: A predicate that matches join points. Advice is associated with a pointcut expression and runs at any join point matched by the pointcut (for example, the execution of a method with a certain name). The concept of join points as matched by pointcut expressions is central to AOP, and Spring uses the AspectJ pointcut expression language by default.

Advice: Action taken by an aspect at a particular join point. Different types of advice includes "around," "before" and "after" advice. Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors around the join point.

Types of advice:

Before advice: Advice that executes before a join point, but which does not have the ability to prevent execution flow proceeding to the join point (unless it throws an exception).

After returning advice: Advice to be executed after a join point completes normally: for example, if a method returns without throwing an exception.

After throwing advice: Advice to be executed if a method exits by throwing an exception.

After (finally) advice: Advice to be executed regardless of the means by which a join point exits (normal or exceptional return).

Around advice: Advice that surrounds a join point such as a method invocation. This is the most powerful kind of advice. Around advice can perform custom behavior before and after the method invocation. It is also responsible for choosing whether to proceed to the join point or to shortcut the advised method execution by returning its own return value or throwing an exception.

Refer to AOP Example for a simple before and after advice configuration.