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Filters & Interceptors

Filter

Filter components are executed by the servlet container for each incoming HTTP request and for each HTTP response. Requests always first pass through Filter instances, before reaching a Servlet.

If the application has multiple custom filters, the order of execution can be defined with @Order annotation.

Interceptor

Spring Interceptors are similar to Servlet Filters. An interceptor just allows custom pre-processing with the option of prohibiting the execution of the handler itself, and custom post-processing, having access to Spring Context.

HandlerInterceptor

HandlerInterceptor instances are executed as part of the request handling inside the DispatcherServlet (which implements javax.servlet.Servlet).

HandlerInterceptor Methods

  • prehandle() – called before the execution of the actual handler
  • postHandle() – called after the handler is executed
  • afterCompletion() – called after the complete request is finished and the view is generated

These methods return a boolean value. It tells Spring to further process the request (true) or not (false). Returning true to send the request further to the handler method. Returning false tells Spring to stop the execution.

Registering HandlerInterceptor

Every interceptor must be registered by overriding addInterceptors() method of WebMvcConfigurer interface.

Filters vs HandlerInterceptors

  • Filter is related to the Servlet API and HandlerIntercepter is a Spring specific concept.
  • Interceptors will only execute after Filters.
  • Fine-grained pre-processing tasks are suitable for HandlerInterceptors (authorization checks, etc.)
  • Content handling related or generic flows are well-suited for Filters (such as multipart forms, zip compression, image handling, logging requests, authentication etc.)
  • Interceptor’s postHandle method will allow you to add more model objects to the view but you can not change the HttpServletResponse since it's already committed.
  • Filter’s doFilter method is much more versatile than Interceptor’s postHandle. You can change the request or response and pass it to the chain or even block the request processing.
  • A HandlerInterceptor gives more fine-grained control than a filter because you have access to the actual target “handler”. You can even check if the handler method has a specific annotation.

Blog References