将对象转成 json 以及 将字符串 hash 加密

        /// <summary>
        /// 生成 Json
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public string ObjToJson(Object obj)
        {
            StringWriter sw;
            JsonSerializer serializer = new JsonSerializer();
            sw = new StringWriter();
            serializer.Serialize(new JsonTextWriter(sw), obj);
            return sw.GetStringBuilder().ToString();
        }