FeignClient throws instead of returning ResponseEntity with error http status

Question

As I\'m using ResponseEntity as return value for my FeignClient method, I was expecting it to return a ResponseEntity with 400 status if it\'s what the

Answer 1

By the way, solution I gave before works, but my initial intention is bad idea: an error is an error and should not be handled on nominal flow. Throwing an exception, like Feign does, and handling it with an @ExceptionHandler is a better way to go in Spring MVC world.

So two solutions:

• add an @ExceptionHandler for FeignException
• configure the FeignClient with an ErrorDecoder to translate the error in an Exception your business layer knows about (and already provide @ExceptionHandler for)

I prefer second solution because received error message structure is likely to change from a client to an other, so you can extract finer grained data from those error with a per-client error decoding.

FeignClient with conf (sorry for the noise introduced by feign-form)

@FeignClient(value = "uaa", configuration = OauthFeignClient.Config.class)
public interface OauthFeignClient {

    @RequestMapping(
            value = "/oauth/token",
            method = RequestMethod.POST,
            consumes = MULTIPART_FORM_DATA_VALUE,
            produces = APPLICATION_JSON_VALUE)
    DefaultOAuth2AccessToken token(Map formParams);

    @Configuration
    class Config {

        @Value("${oauth.client.password}")
        String oauthClientPassword;

        @Autowired
        private ObjectFactory messageConverters;

        @Bean
        public Encoder feignFormEncoder() {
            return new SpringFormEncoder(new SpringEncoder(messageConverters));
        }

        @Bean
        public Decoder springDecoder() {
            return new ResponseEntityDecoder(new SpringDecoder(messageConverters));
        }

        @Bean
        public Contract feignContract() {
            return new SpringMvcContract();
        }

        @Bean
        public BasicAuthRequestInterceptor basicAuthRequestInterceptor() {
            return new BasicAuthRequestInterceptor("web-client", oauthClientPassword);
        }

        @Bean
        public ErrorDecoder uaaErrorDecoder(Decoder decoder) {
            return (methodKey, response) -> {
                try {
                    OAuth2Exception uaaException = (OAuth2Exception) decoder.decode(response, OAuth2Exception.class);
                    return new SroException(
                            uaaException.getHttpErrorCode(),
                            uaaException.getOAuth2ErrorCode(),
                            Arrays.asList(uaaException.getSummary()));

                } catch (Exception e) {
                    return new SroException(
                            response.status(),
                            "Authorization server responded with " + response.status() + " but failed to parse error payload",
                            Arrays.asList(e.getMessage()));
                }
            };
        }
    }
}

Common business exception

public class SroException extends RuntimeException implements Serializable {
    public final int status;

    public final List errors;

    public SroException(final int status, final String message, final Collection errors) {
        super(message);
        this.status = status;
        this.errors = Collections.unmodifiableList(new ArrayList<>(errors));
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof SroException)) return false;
        SroException sroException = (SroException) o;
        return status == sroException.status &&
                Objects.equals(super.getMessage(), sroException.getMessage()) &&
                Objects.equals(errors, sroException.errors);
    }

    @Override
    public int hashCode() {
        return Objects.hash(status, super.getMessage(), errors);
    }
}

Error handler (extracted from a ResponseEntityExceptionHandler extension)

@ExceptionHandler({SroException.class})
public ResponseEntity