code: public static <T extends AbstractJaxb> List<T> getDescendants(T target,
              List<T> resultList, String clazz) {
          return execute(target, resultList, null, clazz);
      }
docs: class属性の指定で子孫要素を返す
  
  @param target
  objects for scan
  @param resultList
  usually, pass new ArrayList
  @param clazz
  class property of tag
  @return