Spring AOP: Aspect Oriented Programming

In this article, we will learn Aspect oriented Concepts with spring

Aspect Oriented Programming

AOP is not specific to Spring Framework, rather its general concept widely used in various frameworks. So why AOP is adopted in Spring Framework, when its rich core concept is built around Dependency Injection?

There are various concerns which cut-across multiple classes/types and are scattered across multiple classes throughout the code in an enterprise application. These crosscutting concerns are

  • Logging
  • Transaction Management
  • Security Management
  • Profiling

To remove all these crosscutting concerns codes scattered across all modules and bring it in one common place thereby achieving modularity. So this way, crosscutting concerns are modularized removing the code from the application and it is implemented using aspects

AOP Terminologies

Aspect: modularization of concerns that are cut across through multiple classes/types

Join Point: set of possible points in the execution of the program such as method execution, exception handling. In Spring AOP, a join point always represents a method execution

Advice: actual advice taken at the join point during program execution

Pointcut: predicates that matches the join point. Poincut expression determines where the actual advice needs to be applied during runtime

Target Object: object being advised by one/more aspects at runtime. But these objects are always proxied object as Spring AOP is implemented using runtime proxies

AOP Proxy:  object created by aspects at runtime. In Spring AOP, AOP proxy is created using JDK dynamic proxy or CGLIB proxy

Weaving: linking aspect with object to create advised object

For details on Spring AOP see here

Advice in Spring

We can implement advices in spring using two approaches

  1. Having advice class which implements respective interfaces for the concenrs
  2. AspectJ based annotations covering crosscutting concerns

Note: we will implement each advice using both approaches in the following articles

Types of advices:

  • Before advice: executes before method execution
    Interface: org.springframework.aop.BeforeAdvice
    Annotation:@Before (org.aspectj.lang.annotation.Before)
  • After returning advice: executes after method execution completes normally
    Interface: org.springframework.aop.AfterReturningAdvice
    Annotation:@AfterReturning (org.aspectj.lang.annotation.AfterReturning)
  • After (finally) advice: executes after method execution irrespective of the outcome
    Interface: org.springframework.aop.AfterAdvice
  • After throwing advice: executes after method throws an exception
    Interface: org.springframework.aop.ThrowsAdvice
    Annotation: @AfterThrowing(org.aspectj.lang.annotation.AfterThrowing)
  • Around advice: executes before & after method execution, but requires proceed() method to continue the execution
    Interface: org.aopalliance.intercept.MethodInterceptor

In the coming discussions, we will extend the above article to see the detailed examples for each advice in separate articles covering both approaches


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Happy Coding !!
Happy Learning !!

Spring AOP: Before Advice