code: public static ParamWrapper newInstance(String key, Object value) {
          Map<String, Object> paramMap = new HashMap<String, Object>(16);
          paramMap.put(key, value);
          return new ParamWrapper(paramMap);
      }
docs: 获取新的ParamWrapper实例，并注入一对key、value的值.
  @param key 键
  @param value 值
  @return ParamWrapper实例