/// <summary> 
        /// DataSet转换为Json 
        /// </summary> 
        /// <param name="dataSet">DataSet对象</param> 
        /// <returns>Json字符串</returns> 
        public static string ToJson(DataSet dataSet)
        {
            string jsonString = "{";
            foreach (DataTable table in dataSet.Tables)
            {
                jsonString += "\"" + table.TableName + "\":" + ToJson(table) + ",";
            }
            jsonString = jsonString.TrimEnd(',');
            return jsonString + "}";
        }

 /// <summary>  
        /// DataSet转换成Json格式  
        /// </summary>  
        /// <param name="ds">DataSet</param> 
        /// <returns></returns>  
        public static string Dataset2Json(DataSet ds)
        {
            StringBuilder json = new StringBuilder();

            foreach (DataTable dt in ds.Tables)
            {
                json.Append("{\"");
                json.Append(dt.TableName);
                json.Append("\":");
                json.Append(DataTable2Json(dt));
                json.Append("}");
            }
            return json.ToString();
        }