Spring 5中的HTTP响应异常处理Reactive

Question

I'm developing some reactive microservices using Spring Boot 2 and Spring 5 with WebFlux reactive starter.

I'm facing the following problem: I want to handle all HTTP Statuses that I receive from calling another REST Services and throws an exception when I receive some bad HTTP Status. For example, when I call an endpoint and I receive an 404 HTTP Status, I want to throw an exception and that exception to be handled in some ExceptionHandler class, just like the way it was in Spring 4 with @ControllerAdvice .

What is the right way to do this? Hope to receive some good suggestions.

Answer 1

This can be addressed in two independent parts.

How to convert HTTP 404 responses received by WebClient into custom exceptions

When using WebClient , you can receive HTTP 404 responses from remote services. By default, all 4xx and 5xx client responses will be turned into WebClientResponseException . So you can directly handle those exceptions in your WebFlux app.

If you'd like to turn only 404 responses into custom exceptions, you can do the following:

WebClient webClient = //...
webClient.get().uri("/persons/1")
  .retrieve()
  .onStatus(httpStatus -> HttpStatus.NOT_FOUND.equals(httpStatus),
                        clientResponse -> Mono.error(new MyCustomException()))
  .bodyToMono(...);

This is obviously done on a per client call basis.

You can achieve the same in a more reusable way with an ExchangeFilterFunction that you can set once and for all on a WebClient instance like this:

WebClient.builder().filter(myExchangeFilterFunction)...

How to handle custom exceptions in WebFlux apps

With Spring WebFlux with annotations, you can handle exceptions with methods annotated with @ExceptionHandler (see Spring Framework reference documentation ).

Note: using a WebExceptionHandler is possible, but it's quite low level as you'll have no high-level support there: you'll need to manually write the response with buffers without any support for serialization.

Answer 2

I think what you are looking for is WebFluxResponseStatusExceptionHandler the check this for reference .

In the WebHandler API, a WebExceptionHandler can be used to to handle exceptions from the chain of WebFilter's and the target WebHandler. When using the WebFlux Config, registering a WebExceptionHandler is as simple as declaring it as a Spring bean, and optionally expressing precedence via @Order on the bean declaration or by implementing Ordered.

This example may help, have not tried it myself.

@Component
@Order(-2)
class RestWebExceptionHandler implements WebExceptionHandler{

    @Override
    public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
        if (ex instanceof PostNotFoundException) {
            exchange.getResponse().setStatusCode(HttpStatus.NOT_FOUND);

            // marks the response as complete and forbids writing to it
            return exchange.getResponse().setComplete();
        }
        return Mono.error(ex);
    }
}

class PostNotFoundException extends RuntimeException {
    PostNotFoundException(String id) {
        super("Post:" + id + " is not found.");
    }
}