What is the implementation principle of Spring AOP?

The implementation principle of SpringAOP is based on the mechanism of dynamic proxy. In SpringAOP, aspects (Aspect) are defined using AspectJ annotations or XML configuration, which contain a set of join points (Join Point) and advices (Advice). Join points indicate the points where advice can be inserted during program execution, while advices define the logic to be executed at those join points.

During the runtime of a program, SpringAOP dynamically creates proxy objects that contain the functionality of the target object and determine when and where to insert advice based on the defined aspect’s logic. Depending on the pointcut for method invocation, SpringAOP can use either JDK dynamic proxy or CGLIB bytecode enhancement technology to implement the proxy. By invoking the proxy object, SpringAOP can execute the corresponding advice logic before, after, or when an exception is thrown during method execution.

SpringAOP supports various types of notifications, including Before Advice, After Advice, After Returning Advice, After Throwing Advice, and Around Advice. These notifications can be specified on which join points to apply through Pointcut expressions.

In summary, the implementation principle of Spring AOP is to use dynamic proxies to proxy the target object, and insert advice at specific join points based on the aspect’s defined logic. This allows developers to separate cross-cutting concerns from business logic, improving code maintainability and reusability.