Java Spring Boot framework - WebClient logging 4xx/5xx body response

Question

I am new to Spring Boot framework's WebClient. How do I only log the 4xx/5xx with its error body only on error, but when success, return back the clientResponse as a String , and we can later using gson to serialize it?

String postResponse =
        post(
            ENDPOINT,
            token,
            request,
            Request.class);

Response response = gson.fromJson(postResponse, Response.class);

    private String post(String endpoint, String token, Mono<?> requestBody, Class<?> requestBodyClass) {

      WebClient.Builder webClientBuilder = WebClient.builder();

      WebClient.RequestBodySpec requestBodySpec = webClientBuilder.build().post().uri(uri);
      requestBodySpec.header(
          "Authorization", BEARER_TOKEN_PREFIX + this.accessTokens.get(token));

      return requestBodySpec
        .header("Content-Type", HEADER_VALUE_CONTENT_TYPE)
        .body(Mono.just(requestBody), requestBodyClass)
        .retrieve()
        .bodyToMono(String.class)
        .block();
    }

Answer 1

May I suggest something like:

    private String post(String endpoint, String token, Mono<?> requestBody, Class<?> requestBodyClass) {
        Mono<String> stringMono = WebClient.builder().build()
                .post()
                .uri(endpoint)
                .body(BodyInserters.fromValue(requestBodyClass))
                .exchange()
                .flatMap(SomeServiceImpl::getResultAsStringOrLog4xx5xx);
        
        //get the JSON from the Mono, but you might not want to block
    }

(I omitted the headers)

And the actual answer to the question, do perform the logging with something similar:

private static Mono<String> getResultAsStringOrLog4xx5xx(ClientResponse response) {
        if (response.statusCode().is2xxSuccessful()) {
            return response.bodyToMono(String.class);
        } else if (response.statusCode().is5xxServerError()) {
            Logger.error(); //up to you
        } else {
//at this point, you can have your logic on error code
        }
        return
    }

There are other ways of doing this, hope this can get you started.

Also, try not to block() in your application.

Thank you