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

So, looking at source code, it seams that only solution is actually using feign.Response as return type for FeignClient methods and hand decoding the body with something like new ObjectMapper().readValue(response.body().asReader(), clazz) (with a guard on 2xx status of course because for error statuses, it's very likely that body is an error description and not a valid payload ;).

This makes possible to extract and forward status, header, body, etc. even if status is not in 2xx range.

Edit: Here is a way to forward status, headers and mapped JSON body (if possible):

public static class JsonFeignResponseHelper {
    private final ObjectMapper json = new ObjectMapper();

    public  Optional decode(Response response, Class clazz) {
        if(response.status() >= 200 && response.status() < 300) {
            try {
                return Optional.of(json.readValue(response.body().asReader(), clazz));
            } catch(IOException e) {
                return Optional.empty();
            }
        } else {
            return Optional.empty();
        }
    }

    public  ResponseEntity toResponseEntity(Response response, Class clazz, Function mapper) {
        Optional payload = decode(response, clazz).map(mapper);

        return new ResponseEntity(
                payload.orElse(null),//didn't find a way to feed body with original content if payload is empty
                convertHeaders(response.headers()),
                HttpStatus.valueOf(response.status()));
    }

    public MultiValueMap  convertHeaders(Map> responseHeaders) {
        MultiValueMap responseEntityHeaders = new LinkedMultiValueMap<>();
        responseHeaders.entrySet().stream().forEach(e -> 
                responseEntityHeaders.put(e.getKey(), new ArrayList<>(e.getValue())));
        return responseEntityHeaders;
    }
}

that can be used as follow:

@PostMapping("/login")
public ResponseEntity getTokens(@RequestBody @Valid LoginRequest userCredentials) throws IOException {
    Response response = oauthFeignClient.token();

    return feignHelper.toResponseEntity(
            response,
            OauthTokenResponse.class,
            oauthTokenResponse -> new LoginTokenPair(
                    new BearerToken(oauthTokenResponse.access_token, oauthTokenResponse.expires_in),
                    new BearerToken(oauthTokenResponse.refresh_token, refreshTokenValidity)));
}

This saves headers and status code, but error message is lost :/