private JsonNode fetchJson(final URL url)
      throws IOException {
    try {
      ObjectMapper objectMapper = new ObjectMapper();
      HttpURLConnection conn = _authenticatedURL.openConnection(url, _token);
      return objectMapper.readTree(conn.getInputStream());
    } catch (AuthenticationException e) {
      logger.error(String.format("Cannot authenticate in Mr Client %s", e.getMessage()));
    } catch (IOException e) {
      logger.error(String.format("Error reading stream in Mr Client %s", e.getMessage()));
    }
    return null;
  }
For a given rest url, fetchs and return the jsonnode

@param url rest job history server url
@return Json node to which the url points
app/com/linkedin/drelephant/exceptions/MRClient.java