How to intercept requests by handler method in Spring WebFlux

Question

I've got following interceptor in Spring MVC that checks if user can access handler method:

class AccessInterceptor : HandlerInterceptorAdapter() {

override fun preHandle(request: HttpServletRequest, response: HttpServletResponse, handler: Any?): Boolean {
    val auth: Auth =
        (if (method.getAnnotation(Auth::class.java) != null) {
            method.getAnnotation(Auth::class.java)
        } else {
            method.declaringClass.getAnnotation(Auth::class.java)
        }) ?: return true
    if (auth.value == AuthType.ALLOW) {
        return true
    }

    val user = getUserFromRequest(request) // checks request for auth token
    // and checking auth for out user in future.
    return renderError(403, response)

In my Controller I do annotate methods, like this:

@GetMapping("/foo")
@Auth(AuthType.ALLOW)
fun doesntNeedAuth(...) { ... }

@GetMapping("/bar")
@Auth(AuthType.ADMIN)
fun adminMethod(...) { ... }

In case if user has wrong token or no permissions, error is being returned.
Is it possible to do this in Spring WebFlux with annotation-style controllers?

Answer 1

To solve that problem I would most probably use:

• A Spring Reactive Web WebFilter from the WebHandler API to intercept the incoming request

• The RequestMappingHandlerMapping to retrieve the method which handles the current request

@Autowired
RequestMappingHandlerMapping requestMappingHandlerMapping;

...
@Override
public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
    ...
    HandlerMethod handler = (HandlerMethod) requestMappingHandlerMapping.getHandler(exchange).toProcessor().peek();
    //your logic
}

Answer 2

     @Component
     class AuditWebFilter(
          private val requestMapping: RequestMappingHandlerMapping
     ): WebFilter {

          override fun filter(exchange: ServerWebExchange, chain: WebFilterChain): Mono<Void> {
               // if not to call - then exchange.attributes will be empty
               // so little early initializate exchange.attributes by calling next line
               requestMapping.getHandler(exchange)

               val handlerFunction = exchange.attributes.get(HandlerMapping.BEST_MATCHING_HANDLER_ATTRIBUTE) as HandlerMethod
               val annotationMethod = handlerFunction.method.getAnnotation(MyAnnotation::class.java)

               // annotationMethod  proccesing here
          }
     }