In a SpringBoot application you want to do something to the request before your controller handles it or to the response before it's returned back to the client.

• General purpose interceptor : runs for all requests
• Single purpose interceptor : runs for a specific controller (and/or) specific URL

All interceptors configurations are done within a configuration class in SpringBoot.

• The interceptor configuration class should implement WebMvcConfigurer
• The configuration class should override the addInterceptors method
• Within the addInterceptors method, use interceptorRegistry to add a specific interceptor to Spring Context, using the addInterceptor method

💡 multiple interceptors could be added to the configuration. Spring provides a lot of options to deal with like the order method to specify the interceptors execution order. addPathPatterns method to deal with specific URL (single purpose interceptor)

To implement interceptors, you should :

• Implement the HandlerInterceptor class
• Override the preHandle, postHandle and afterCompletion methods

💡 preHandle will be executed before the request reaches then handler (controller) : it returns a boolean; if false then the interceptor will be the last step of the request handling (controller will not be executed) postHandle will be executed after the handler (controller) already served the request afterCompletion will be executed after the reauest and the view rendering, in case a view engine is executed