/// <summary>
        /// 返回解码后的字符串
        /// </summary>
        /// <param name="key">传参的参数名</param>
        /// <returns></returns>
        public static string UrlDecode(string key)
        {
            string input = GetUrlParam(key).ToLower();
            if (input.Length == 0)
                return string.Empty;
            //首先用utf-8进行解码
            string result = HttpUtility.UrlDecode(input, Encoding.UTF8);
            // 将已经解码的字符再次进行编码.            
            string encode = HttpUtility.UrlEncode(result, Encoding.UTF8).ToLower();
            //与原来编码进行对比，如果不一致说明解码未正确，用gb2312进行解码
            if (input != encode)
                result = HttpUtility.UrlDecode(input, Encoding.GetEncoding("gb2312"));
            return result;
        }

        private static string GetUrlParam(string key)
        {
            if (System.Web.HttpContext.Current != null)
            {
                string query = HttpContext.Current.Request.Url.Query;
                if (query != null && query.Length > 0)
                {
                    int index = 0;
                    index = query.IndexOf(key + "=");
                    if (index >= 0)
                    {
                        query = query.Substring(key.Length + 1 + index);
                        index = query.IndexOf('&');
                        if (index >= 0)
                            query = query.Substring(0, index);
                        return query;
                    }
                }
            }
            return string.Empty;
        }