ResponseEntityExceptionHandler returns empty response body for 401 exceptions

Question

I'm trying to implement a Rest call to an authentication server using RestTemplate and log the response in case the server returns an exception. In order to do this, I used a ResponseEntityExceptionHandler to handle HttpClientErrorException's and HttpServerErrorException's.

public Response sendRequest(Request requestBody, String url, HttpMethod httpMethod, Response responseBody) {
    RestTemplate restTemplate = new RestTemplate();
    HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(requestBody.getBody(),
            this.securityHeaders);
    ResponseEntity<? extends Response> response = restTemplate.exchange(url, httpMethod, request,
            responseBody.getClass());
    return response.getBody();
}

Currently my ResponseEntityExceptionHandler is the following

@ControllerAdvice
public class RestResponseExceptionHandler extends ResponseEntityExceptionHandler {

private static Logger log = LoggerFactory.getLogger(RestResponseExceptionHandler.class);
private HttpHeaders headers = new HttpHeaders();

@ExceptionHandler(value = { HttpClientErrorException.class, HttpServerErrorException.class })
protected ResponseEntity<Object> handleConflict(HttpStatusCodeException ex, WebRequest request) {
    ErrorMessage responseBody = new ErrorMessage();
    try {
        JSONObject bodyOfException = new JSONObject(ex.getResponseBodyAsString());
        log.warn("{}| {}", ex.getStatusCode(), bodyOfException);
        responseBody.setErrorAndDescription(bodyOfException.optString("error"),
                bodyOfException.optString("error_description"));
    } catch (JSONException e) {
        log.error("{}| Bad authentication response body | Response Body | {}", ex.getStatusCode(),
                ex.getResponseBodyAsString());
    }

    return handleExceptionInternal(ex, responseBody, headers, ex.getStatusCode(), request);
}

}

However, only for HttpStatus 401 exceptions, I get an empty Response Body.

Example of logs:

400| {"error_description":"Bad client credentials","error":"invalid_client"}

401| Bad authentication response body | Response Body | 

Does anyone know how I can obtain the response body for 401 exceptions?

Edit: When using a Postman to call the Authentication Server I get non null 401 responseBody:

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

Answer 1

I was finally able to log the response body for 401 Exceptions. I added the dependency

org.apache.httpcomponents:httpclient

and configured Rest Template Request Factory

    restTemplate.setRequestFactory(new HttpComponentsClientHttpRequestFactory());

Apparently the default request factory SimpleClientHttpRequestFactory is not able to read the response body for 401 Http Status.