code: public static void readField(JsonParser jsonParser,
                                 String expectedFieldName) throws IOException {
      readToken(jsonParser, expectedFieldName, JsonToken.FIELD_NAME);
      String fieldName = jsonParser.getCurrentName();
      if (!fieldName.equals(expectedFieldName)) {
        foundUnknownField(fieldName, expectedFieldName);
      }
    }
docs: The method reads a field from the JSON stream, and checks if the
  field read is the same as the expect field.
  
  @param jsonParser The JsonParser instance to be used
  @param expectedFieldName The field name which is expected next
  @throws IOException