Aspect Oriented Programming in Spring

AOP is an acronym for Aspect Oriented Programming. AOP provides the ability to implement crosscutting logic—that is, logic that applies to many parts of your application—in a single place and to have that logic applied across your application automatically. There are two main kinds of AOP implementation. Static AOP, such as AspectJ (www.aspectj.org), provides a compile-time solution for building AOP-based logic and adding it to an application. Dynamic AOP, such as that in Spring, allows crosscutting logic to be applied arbitrarily to any other code at runtime. Wthin the Spring framework itself, AOP is used for many purposes, particularly in transaction management. You can think of Spring's AOP implementation as coming in two logical parts. The first part is the AOP core, which provides fully decoupled, purely programmatic AOP functionality. The second part of the AOP implementation is the set of framework services that make AOP easier to use in your applications. Spring AOP is really a subset of the full AOP feature set, implementing only a handful of the constructs available in implementations like AspectJ. The core architecture of Spring AOP is based around proxies. When you want to create an advised instance of a class, you must use the ProxyFactory class to create a proxy of an instance of that class, first providing the ProxyFactory with all the aspects that you want to be woven into the proxy. Internally, Spring has two proxy implementations: JDK dynamic proxy and CGLIB proxy. In previous releases of Spring, there was not much difference between the two proxy types, and CGLIB proxies were only used when you wanted to proxy classes rather than interfaces, or when you explicitly specified them. As of the 1.1 release of Spring, the CGLIB proxy is noticeably faster than JDK dynamic proxies in most cases. The ProxyFactory class controls the weaving and proxy creation process in Spring AOP

Chapter 6. Aspect Oriented Programming with Spring

6.1. 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. (Such concerns are often termed crosscutting concerns in AOP literature.)

One of the key components of Spring is the AOP framework. While the Spring IoC container does not depend on AOP, meaning you do not need to use AOP if you don't want to, AOP complements Spring IoC to provide a very capable middleware solution.