Spring WebClient - Customised response callback on HTTP error status

wild_nothing :

I need to make another HTTP call in the case that my WebClient request receives a HTTP 4xx or 5xx error.

Currently I have the following:

webClient.post()
         .uri(myUri)
         .headers(myHeaders)
         .body(myBody)
         .retrieve()
         .onStatus(HttpStatus::isError, responseStrategy::errorResponseCallback)
         ...

My error response callback looks like this:

    public Mono<? extends Throwable> errorResponseCallback(ClientResponse clientResponse) {
        ... make ugly new HTTP request here 

        return Mono.error(...);
    }

I don't like the idea of embedding error handling in the callback which is only supposed to return a Mono containing an exception.

What is the correct approach for this situation?

Bogdan Oros :

In case you want to simulate some fallback-based logic, you may use onErrorResume method and the fallback function result will be passed to the downstream. The WebClient will threat non-successful results as errors, so onErrorResume is called.

webClient.post()
         .uri(myUri)
         .headers(myHeaders)
         .body(myBody)
         .retrieve()
         .bodyToMono(String.class)
         .onErrorResume(error -> ... your fallback logic ...)

In case you just want to perform some side-effect, and you want to keep the error to go through the reactive stream, you may use:

webClient.post()
         .uri(myUri)
         .headers(myHeaders)
         .body(myBody)
         .retrieve()
         .bodyToMono(String.class)
         .doOnError(error -> ... your fallback logic ...)