Explanation for important Questions

Concern is behavior which we want to have in a module of an application. Concern may be defined as a functionality we want to implement to solve a specific business problem. E.g. in any eCommerce application different concerns (or modules) may be inventory management, shipping management, user management etc.

Cross-cutting concern is a concern which is applicable throughout the application (or more than one module). e.g. logging , security and data transfer are the concerns which are needed in almost every module of an application, hence they are termed as cross-cutting concerns.

Main java based AOP implementations are listed below:

  1. AspectJ

  2. Spring AOP

  3. JBoss AOP

Join point is a point of execution of the 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. For example, all the methods defined inside your EmployeeManager interface cab be considered joint points if you apply any cross-cutting concern of them.

Pointcut is a predicate or expression that matches join points. Advice is associated with a pointcut expression and runs at any join point matched by the pointcut (for example, expression “execution(* EmployeeManager.getEmployeeById(..))” to match getEmployeeById() the method in EmployeeManagerinterface). The concept of join points as matched by pointcut expressions is central to AOP, and Spring uses the AspectJ pointcut expression language by default.

A proxy is a well-used design pattern. To put it simply, a proxy is an object that looks like another object, but adds special functionality behind the scene.

Spring AOP is proxy-based. AOP proxy is an object created by the AOP framework in order to implement the aspect contracts in runtime.

The Spring AOP framework supports only limited types of AspectJ pointcuts and allows aspects to apply to beans declared in the IoC container. If you want to use additional pointcut types or apply your aspects “to objects created outside the Spring IoC container“, you have to use the AspectJ framework in your Spring application and use it’s weaving feature.

Weaving is the process of linking aspects with other outsider 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 only. In contrast, the AspectJ framework supports both compile-time and load-time weaving.