FeignClient throws instead of returning ResponseEntity with error http status - spring-cloud-feign

Question

As I'm using ResponseEntity<T> as return value for my FeignClient method, I was expecting it to return a ResponseEntity with 400 status if it's what the server returns. But instead it throws a FeignException.
How can I get a proper ResponseEntity instead of an Exception from FeignClient ?
Here is my FeignClient:
#FeignClient(value = "uaa", configuration = OauthFeignClient.Conf.class)
public interface OauthFeignClient {
#RequestMapping(
value = "/oauth/token",
method = RequestMethod.POST,
consumes = MULTIPART_FORM_DATA_VALUE,
produces = APPLICATION_JSON_VALUE)
ResponseEntity<OauthTokenResponse> token(Map<String, ?> formParams);
class Conf {
#Value("${oauth.client.password}")
String oauthClientPassword;
#Bean
public Encoder feignFormEncoder() {
return new SpringFormEncoder();
}
#Bean
public Contract feignContract() {
return new SpringMvcContract();
}
#Bean
public BasicAuthRequestInterceptor basicAuthRequestInterceptor() {
return new BasicAuthRequestInterceptor("web-client", oauthClientPassword);
}
}
}
and here how I use it:
#PostMapping("/login")
public ResponseEntity<LoginTokenPair> getTokens(#RequestBody #Valid LoginRequest userCredentials) {
Map<String, String> formData = new HashMap<>();
ResponseEntity<OauthTokenResponse> response = oauthFeignClient.token(formData);
//code never reached if contacted service returns a 400
...
}

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<String, ?> formParams);
#Configuration
class Config {
#Value("${oauth.client.password}")
String oauthClientPassword;
#Autowired
private ObjectFactory<HttpMessageConverters> 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<String> errors;
public SroException(final int status, final String message, final Collection<String> 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<Object> handleSroException(SroException ex) {
return new SroError(ex).toResponse();
}
Error response DTO
#XmlRootElement
public class SroError implements Serializable {
public final int status;
public final String message;
public final List<String> errors;
public SroError(final int status, final String message, final Collection<String> errors) {
this.status = status;
this.message = message;
this.errors = Collections.unmodifiableList(new ArrayList<>(errors));
}
public SroError(final SroException e) {
this.status = e.status;
this.message = e.getMessage();
this.errors = Collections.unmodifiableList(e.errors);
}
protected SroError() {
this.status = -1;
this.message = null;
this.errors = null;
}
public ResponseEntity<Object> toResponse() {
return new ResponseEntity(this, HttpStatus.valueOf(this.status));
}
public ResponseEntity<Object> toResponse(HttpHeaders headers) {
return new ResponseEntity(this, headers, HttpStatus.valueOf(this.status));
}
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof SroError)) return false;
SroError sroException = (SroError) o;
return status == sroException.status &&
Objects.equals(message, sroException.message) &&
Objects.equals(errors, sroException.errors);
}
#Override
public int hashCode() {
return Objects.hash(status, message, errors);
}
}
Feign client usage notice how errors are transparently handled (no try / catch) thanks to #ControllerAdvice & #ExceptionHandler({SroException.class})
#RestController
#RequestMapping("/uaa")
public class AuthenticationController {
private static final BearerToken REVOCATION_TOKEN = new BearerToken("", 0L);
private final OauthFeignClient oauthFeignClient;
private final int refreshTokenValidity;
#Autowired
public AuthenticationController(
OauthFeignClient oauthFeignClient,
#Value("${oauth.ttl.refresh-token}") int refreshTokenValidity) {
this.oauthFeignClient = oauthFeignClient;
this.refreshTokenValidity = refreshTokenValidity;
}
#PostMapping("/login")
public ResponseEntity<LoginTokenPair> getTokens(#RequestBody #Valid LoginRequest userCredentials) {
Map<String, String> formData = new HashMap<>();
formData.put("grant_type", "password");
formData.put("client_id", "web-client");
formData.put("username", userCredentials.username);
formData.put("password", userCredentials.password);
formData.put("scope", "openid");
DefaultOAuth2AccessToken response = oauthFeignClient.token(formData);
return ResponseEntity.ok(new LoginTokenPair(
new BearerToken(response.getValue(), response.getExpiresIn()),
new BearerToken(response.getRefreshToken().getValue(), refreshTokenValidity)));
}
#PostMapping("/logout")
public ResponseEntity<LoginTokenPair> revokeTokens() {
return ResponseEntity
.ok(new LoginTokenPair(REVOCATION_TOKEN, REVOCATION_TOKEN));
}
#PostMapping("/refresh")
public ResponseEntity<BearerToken> refreshToken(#RequestHeader("refresh_token") String refresh_token) {
Map<String, String> formData = new HashMap<>();
formData.put("grant_type", "refresh_token");
formData.put("client_id", "web-client");
formData.put("refresh_token", refresh_token);
formData.put("scope", "openid");
DefaultOAuth2AccessToken response = oauthFeignClient.token(formData);
return ResponseEntity.ok(new BearerToken(response.getValue(), response.getExpiresIn()));
}
}

Answer 2

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 <T> Optional<T> decode(Response response, Class<T> 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 <T, U> ResponseEntity<U> toResponseEntity(Response response, Class<T> clazz, Function<? super T, ? extends U> mapper) {
Optional<U> 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<String, String> convertHeaders(Map<String, Collection<String>> responseHeaders) {
MultiValueMap<String, String> 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<LoginTokenPair> 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 :/