Implement Feign ErrorDecoder that is aware of spring HttpClientErrorException and HttpServerErrorException

[xyloman]

In our consumption of feign we ran into an issue where we need access to the response status code and response body associated to a client error. We have implemented the following ErrorDecoder implementation in our code base and wanted to share it with the community. It seems like others that are familiar with spring RestOperations are accustom to HttpClientErrorException and HttpServerErrorException exception trees versus the stripped down FeignException. The only concern with the implementation below is how to handle the response body if an exception where to happen during the copying process from feign response to a given instance of spring HttpStatusCodeException:

public class SpringWebClientErrorDecoder implements ErrorDecoder {

    private ErrorDecoder delegate = new ErrorDecoder.Default();

    @Override
    public Exception decode(String methodKey, Response response) {
        HttpHeaders responseHeaders = new HttpHeaders();
        response.headers().entrySet().stream()
                .forEach(entry -> responseHeaders.put(entry.getKey(), new ArrayList<>(entry.getValue())));

        HttpStatus statusCode = HttpStatus.valueOf(response.status());
        String statusText = response.reason();

        byte[] responseBody;
        try {
            responseBody = IOUtils.toByteArray(response.body().asInputStream());
        } catch (IOException e) {
            throw new RuntimeException("Failed to process response body.", e);
        }

        if (response.status() >= 400 && response.status() <= 499) {
            return new HttpClientErrorException(statusCode, statusText, responseHeaders, responseBody, null);
        }

        if (response.status() >= 500 && response.status() <= 599) {
            return new HttpServerErrorException(statusCode, statusText, responseHeaders, responseBody, null);
        }
        return delegate.decode(methodKey, response);
    }
}

[spencergibb]

The feign support includes support for returning a ResponseEntity<MyObject> which gives you access to the status code, headers and body.

@FeignClient
interface TestClient {
    @RequestMapping(method = RequestMethod.GET, value = "/helloresponse")
    public ResponseEntity<Hello> getHelloResponse();
}

[xyloman]

Updated our code to use the ResponsEntity. Works great. It would be useful if there was something adding to the spring cloud documentation around this topic. If there is something I apologize for missing it.

[spencergibb]

Nope, opened #319

[xyloman]

We started to do more integration testing and this appears to be working slightly different than I expected based upon your comment of using the ResponseEntity. Our use case is to handle a rest API that would return a 409 in the case of a conflict and a 201 in the case of a resource that is created. In these two scenarios the 409 results in a FeignException and the 201 results in a null object being returned instead of a resource entity. The 201 null object response we can account for. However, I was hoping that the 409 would result in a populated ResponseEntity. We also experience this in the case of a 400.

[spencergibb]

Pull requests are welcome.

[bogdatov]

When I use

@FeignClient("usermanagement")
public interface UserClient {
    @RequestMapping(method = RequestMethod.GET, value = "/um/v1/user/{secLoginId}", produces = "application/json")
    ResponseEntity<List<SecUserDTO>> getUsersWithHeader(@PathVariable("secLoginId") String secLoginId);
}

and then getUsersWithHeader returns 404, in exception (FeignException) e .g. like this:

feign.FeignException: status 404 reading UserClient#getUsersWithHeader(String); content:
{
  "httpStatus" : "NOT_FOUND",
  "code" : "U001",
  "message" : "User [ blah ] not found",
 }

How do I determine that I got 404 ? I thought if I wrap it into ResponseEntity, I wont get Exception, but I'm still getting FeignException. Here is my call:

try
        {
        ResponseEntity<List<SecUserDTO>> response = userClient.getUsersWithHeader(loginId);
        if (response.getStatusCode().equals(HttpStatus.OK))
        {
            List<SecUserDTO> userList = response.getBody();
            log.info("userList :{}", userList );
            if (userList != null && userList.size()>0)
            {
                returnUser=userList.get(0);
            }
        }
        else
        {
            log.error("Got error code:{} headers:{}", response.getStatusCode(), response.getHeaders());
        }

        }
        catch(Exception e)
        {
            log.error("Exception:",e);
        }

How do I call getUsersWithHeader and determine if I get 404 ?

[spencergibb]

@bogdatov you need to use a create a feign.ErrorDecoder.

[renatojava]

How I can registermy feign.ErrorDecoder with FeignClient?

Why Error 404 is not catch by ResponseEntity with FeignClient?

[spencergibb]

How I can registermy feign.ErrorDecoder with FeignClient?

See the docs Overriding Feign Defaults for how to register your ErrorDecoder.

Why Error 404 is not catch by ResponseEntity with FeignClient?

Because feign throws an error, though feign 8.12 will change that.

[renatojava]

Thanks.

[agupta1989]

@spencergibb I implemented ErrorDecoder, but not able to get the exact error response message. Inside Response only getting reason and status. can we get detail message like as follows:

{"error":"invalid_token","error_description":"Token was not recognised"}

(this error is thrown by Spring oauth2 server and I was calling it through one service to authorize token)

do we need any additional configuration ? will FeignClientConfiguration help in this ?

[starlight36]

Hi, I think automatically decode exception objects depend on the declared thrown types maybe a good idea. Just like:

@FeignClient
interface TestClient {
    @RequestMapping(method = RequestMethod.GET, value = "/hello/{name}")
    public Hello getHelloResponse(@Param("name") String name) thrown InvalidNameException;
}

@ResponseStatus(HttpStatus.BAD_REQUEST)
class InvalidNameException extends IllegalArgumentException {
    // ...
}

If the response status is BAD_REQUEST, it will decode and throw InvalidNameException automatically. If the method has more than one declared exception types, the decoder will choose one by some kind of conditions, like the ResponseStatus annotation on the InvalidNameException.

[mutisyap]

I used
@AuthorizedFeignClient
Instead of the default Feign Client and the issue is solved