Spring AOP and AspectJ Introduction

Aspect-Oriented Programming (AOP) complements Object-Oriented Programming (OOP) by providing another way of thinking about program structure. The key unit of modularity in OOP is the class, whereas in AOP the unit of modularity is the aspect. Aspects enable the modularization of concerns such as transaction management that cut across multiple types and objects.

The advantages of Spring AOP is it provides declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management. It allow users to implement custom aspects, complementing their use of OOP with AOP. Lets look at AOP concepts and terminolog:

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

2) 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.

3) Advice: action taken by an aspect at a particular join point. Different types of advice include "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.

4) 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.

5) Introduction: declaring additional methods or fields on behalf of a type. Spring AOP allows you to introduce new interfaces (and a corresponding implementation) to any advised object. For example, you could use an introduction to make a bean implement an IsModified interface, to simplify caching.

6) Target object: object being advised by one or more aspects. Also referred to as the advised object. Since Spring AOP is implemented using runtime proxies, this object will always be a proxied object.

7) AOP proxy: an object created by the AOP framework in order to implement the aspect contracts (advise method executions and so on). In the Spring Framework, an AOP proxy will be a JDK dynamic proxy or a CGLIB proxy.

8) Weaving: linking aspects with other application types or objects to create an advised object. This can be done at compile time (using the AspectJ compiler, for example), load time, or at runtime. Spring AOP, like other pure Java AOP frameworks, performs weaving at runtime.

In this page you will find more examples for spring AOP and AspectJ concepts.

Reference: Aspect Oriented Programming with Spring

Spring AOP and AspectJ Examples

1. Spring AOP Advices - Before advice example - xml based configuration
2. Spring AOP Advices - After returning advice example - xml based configuration
3. Spring AOP Advices - After throwing advice example - xml based configuration
4. Spring AOP Advices - Around advice example - xml based configuration
5. Spring AOP Advice - Pointcuts – Name match example
6. Spring AOP Advice - Pointcuts – Regular expression example
7. Spring AOP - AspectJ - @Before example
8. Spring AOP - AspectJ - @After example
9. Spring AOP - AspectJ - @AfterReturning example
10. Spring AOP - AspectJ - @AfterThrowing example
11. Spring AOP - AspectJ - @Around example