Custom Pointcuts and Annotations

Spring AOP provides a flexible mechanism for targeting specific join points in your application by allowing you to define custom pointcuts. These pointcuts specify where advice should be applied and can be created using annotations to increase precision and maintainability.

When you define a custom annotation, such as @Loggable, you are creating a marker that can be placed on methods or classes. Spring's AOP infrastructure scans your application's classes at runtime, searching for these annotations. This scanning process is performed by the proxy creation subsystem, which inspects the bytecode of beans as they are instantiated by the Spring container.

To connect your custom annotation to advice, you create a pointcut expression using the @Pointcut annotation and reference your custom annotation within the expression. For example, the pointcut might use @annotation(com.example.Loggable) to match any method annotated with @Loggable. When the bean is created, Spring analyzes the class and method signatures, checking for the presence of the specified annotation. If a match is found, the proxy infrastructure records that this method should be intercepted.

At runtime, when a method call is made on a proxied bean, Spring's AOP proxy intercepts the call. The proxy checks the method against all registered pointcuts. If the method matches a pointcut defined by your annotation, the associated advice is executed. This matching process is efficient, as Spring maintains a mapping of pointcuts to methods during bean creation, so the runtime check is a simple lookup rather than a repeated scan.

Advice is applied in the order configured by your aspect definitions. The advice itself can be of any type—@Before, @After, or @Around—and is invoked only if the method matches the custom annotation-based pointcut. This approach allows you to modularize cross-cutting concerns and apply them declaratively, without modifying business logic.

By leveraging custom annotations and pointcuts, Spring AOP enables fine-grained control over where and how advice is applied, all managed dynamically by the Spring container at runtime.