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HTTP Response Exception Handling In Spring 5 Reactive

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.

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Answer

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.

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source: stackoverflow.com
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