code: public String getFieldName() throws IOException {
      if (jsonParser.getCurrentToken() != JsonToken.FIELD_NAME) {
        throw new IOException("Expected a field of type " + JsonToken.FIELD_NAME +
                              ", but found a field of type " +
                              jsonParser.getCurrentToken());
      }
      return jsonParser.getCurrentName();
    }
docs: If the current token is a field name, this method returns the name of
  the field.
  
  @return A String object containing the name of the field
  @throws IOException