HandlerInterceptor

HandlerInterceptor is an interface in the Spring Framework that is used to intercept all requests and responses between the client and server. It is a powerful mechanism to perform pre-processing and post-processing tasks on the request and response objects, such as logging, authentication, authorization, and caching.

This interface defines three methods:

1. preHandle() - This method is executed before the actual handler method is called. It allows us to perform pre-processing of the request, such as checking for authentication and authorization, logging, and setting up the response object.

2. postHandle() - This method is executed after the handler method is called but before the view is rendered. It allows us to perform post-processing of the request, such as adding new attributes to the model, modifying the view name, and adding response headers.

3. afterCompletion() - This method is executed after the view is rendered and the response is sent back to the client. It allows us to perform tasks such as logging, cleaning up resources, and handling any errors that may have occurred during the request processing.

HandlerInterceptor is typically used in web applications to implement cross-cutting concerns, such as security, caching, and logging, without cluttering up the controller code. It can be configured using the Spring configuration file or annotations, and can be applied globally or to specific handler methods.