Spring Boot web Client

Question

I am having an issue with the web client.

I am trying to make a post request. The request is good. The thing is, if I add onStatus in order to handle http error codes, I am getting a NPE when calling bodyToMono. If I remove onStatus, I get the response.

we could take this as an example:

Employee createdEmployee = webClient.post()
        .uri("/employees")
        .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
        .body(Mono.just(empl), Employee.class)
        .retrieve()
 .onStatus(HttpStatus::isError, clientResponse -> {
          if (clientResponse.statusCode() == HttpStatus.resolve(402)) {
            return Mono.error(new Exception("402"));
          }
          log.error("Error endpoint with status code {}", clientResponse.statusCode());
          if (clientResponse.statusCode() == HttpStatus.resolve(500)) {
            return Mono.error(new Exception("500"));
          }
          if (clientResponse.statusCode() == HttpStatus.resolve(512)) {
            return Mono.error(new Exception("512"));
          }
          return Mono.error(new Exception("Error while processing request"));
        })
        .bodyToMono(Employee.class);

I wan to handle 4xx and 5xx errors including their specific subtypes (404,402) 500, 512

Answer 1

Before bodyToMono() you can use onStatus()

.onStatus(httpStatus -> {
    return httpStatus.is4xxClientError(); // handle 4xx or use .is5xxServerError() or .value()
}, clientResponse -> Mono.error(new RuntimeException("custom exception")))

Another option is to use ExchangeFilterFunction and apply it to your webclient

ExchangeFilterFunction responseErrorHandler =
        ExchangeFilterFunction.ofResponseProcessor(clientResponse -> {
            clientResponse.statusCode(); // handle any status manually
            return Mono.just(clientResponse);
        });

WebClient webClient = WebClient.builder()
        .filter(responseErrorHandler)