AOP - Aspect Oriented Programming

1. What is AOP?

AOP is used to separate functionalities that are not related to the core business logic. In another word, it is used to decouple cross-cutting concerns from the core business logic. (e.g. logging, exception handling) Cross-cutting concerns are aspects of your application that affect multiple components, such as logging, security, or performance.

For example, logging is a cross-cutting concern because it is used in many places in the application. It is not related to the core business logic. So, it is a good idea to separate logging from the core business logic. This is where AOP comes into the picture.

2. AOP Concepts

2.1. Join Point

Join point is a point in the execution of the application where an aspect can be plugged in. In another word, it is the unit of point can be monitored.

This point could be a method being called, an exception being thrown, or even a field being modified. In Spring AOP, a join point always represents a method execution.

2.2. Pointcut (Designator)

Pointcut is a predicate or expression that matches join points. It is a set of join points where advice should be executed.

2.3. Advice

Advice is the action taken by an aspect at a particular join point. Different types of advice include before, after, after-returning, after-throwing, and around advice.

2.4. Aspect

Aspect is a module that encapsulates join points, pointcuts, and advice. It is a class that implements cross-cutting concerns.

Spring AOP works (proxy pattern)

Spring AOP works by using proxy to wrap the object being called. The proxy is created by the Spring container and is used to intercept the calls to the object being proxied. This is a decoupling work to monitor the application without modifying the core business logic.