Interception

All HandlerMapping implementations support handler interceptors, which are useful if you need to apply specific functionality to specific requests - for example, checking for the presence of a main request. Interceptors must implement HandlerInterceptor from the org.springframework.web.servlet package with three methods that should provide enough flexibility to perform all kinds of pre- and post-processing:

• preHandle(..): Before the actual handler is executed

• postHandle(..): After the handler is executed

• afterCompletion(..): After the request is completed

The preHandle(..) method returns a Boolean value. This method can be used to interrupt or continue processing of the execution chain. If this method returns true, the handler execution chain continues. If it returns false, DispatcherServlet assumes that the interceptor itself has processed the requests (and, for example, rendered the corresponding view), and does not continue executing other interceptors and the actual handler in the execution chain.

You can also register them directly using setters in separate HandlerMapping implementations.

The postHandle method is less useful when using methods marked with the @ResponseBody annotation and ResponseEntity methods for which the message is written and captured within the HandlerAdapter and before postHandle. This means that it will be too late to make any changes to the message, such as adding an extra header. For such scenarios, you can implement ResponseBodyAdvice and either declare it as an Advice controller bean, or configure it directly for RequestMappingHandlerAdapter.