what is the right way to handle errors in spring-webflux

Question

I've been doing some research using spring-webflux and I like to understand what should be the right way to handle errors using Router Functions.

I've created an small project to test a couple of scenarios, and I like to get feedback about it, and see what other people is doing.

So far what I doing is.

Giving the following routing function:

@Component public class HelloRouter {     @Bean     RouterFunction<?> helloRouterFunction() {         HelloHandler handler = new HelloHandler();         ErrorHandler error = new ErrorHandler();          return nest(path("/hello"),                 nest(accept(APPLICATION_JSON),                         route(GET("/"), handler::defaultHello)                                 .andRoute(POST("/"), handler::postHello)                                 .andRoute(GET("/{name}"), handler::getHello)                 )).andOther(route(RequestPredicates.all(), error::notFound));     } } 

I've do this on my handler

class HelloHandler {      private ErrorHandler error;      private static final String DEFAULT_VALUE = "world";      HelloHandler() {         error = new ErrorHandler();     }      private Mono<ServerResponse> getResponse(String value) {         if (value.equals("")) {             return Mono.error(new InvalidParametersException("bad parameters"));         }         return ServerResponse.ok().body(Mono.just(new HelloResponse(value)), HelloResponse.class);     }      Mono<ServerResponse> defaultHello(ServerRequest request) {         return getResponse(DEFAULT_VALUE);     }      Mono<ServerResponse> getHello(ServerRequest request) {         return getResponse(request.pathVariable("name"));     }      Mono<ServerResponse> postHello(ServerRequest request) {         return request.bodyToMono(HelloRequest.class).flatMap(helloRequest -> getResponse(helloRequest.getName()))                 .onErrorResume(error::badRequest);     } } 

Them my error handler do:

class ErrorHandler {      private static Logger logger = LoggerFactory.getLogger(ErrorHandler.class);      private static BiFunction<HttpStatus,String,Mono<ServerResponse>> response =     (status,value)-> ServerResponse.status(status).body(Mono.just(new ErrorResponse(value)),             ErrorResponse.class);      Mono<ServerResponse> notFound(ServerRequest request){         return response.apply(HttpStatus.NOT_FOUND, "not found");     }      Mono<ServerResponse> badRequest(Throwable error){         logger.error("error raised", error);         return response.apply(HttpStatus.BAD_REQUEST, error.getMessage());     } } 

Here is the full sample repo:

https://github.com/LearningByExample/reactive-ms-example

Answer 1

If you think, router functions are not the right place to handle exceptions, you throw HTTP Exceptions, that will result in the correct HTTP Error codes. For Spring-Boot (also webflux) this is:

  import org.springframework.http.HttpStatus;   import org.springframework.web.server.ResponseStatusException;   .   .   .     new ResponseStatusException(HttpStatus.NOT_FOUND,  "Collection not found");}) 

spring securities AccessDeniedException will be handled correctly, too (403/401 response codes).

If you have a microservice, and want to use REST for it, this can be a good option, since those http exceptions are quite close to business logic, and should be placed near the business logic in this case. And since in a microservice you shouldn't have to much businesslogic and exceptions, it shouldn't clutter your code, too... (but of course, it all depends).

Answer 2

Spring 5 provides a WebHandler, and in the JavaDoc, there's the line:

Use HttpWebHandlerAdapter to adapt a WebHandler to an HttpHandler. The WebHttpHandlerBuilder provides a convenient way to do that while also optionally configuring one or more filters and/or exception handlers.

Currently, the official documentation suggests that we should wrap the router function into an HttpHandler before booting up any server:

HttpHandler httpHandler = RouterFunctions.toHttpHandler(routerFunction); 

With the help of WebHttpHandlerBuilder, we can configure custom exception handlers:

HttpHandler httpHandler = WebHttpHandlerBuilder.webHandler(toHttpHandler(routerFunction))   .prependExceptionHandler((serverWebExchange, exception) -> {        /* custom handling goes here */       return null;    }).build();