To convert the DataSet to the JsonString

[AjaxPro.AjaxMethod]
    public string GetContractJsonString()
    {
var dataSource = ContractServiceInstance.SelectContractList(cultureName, lessorName, customerId);
        return dataSource.ToJsonString();
}

 /// <summary>
    /// ToJSONString
    /// </summary>
    /// <param name="ds"></param>
    /// <returns></returns>
    public static string ToJsonString(this DataSet ds)
    {
        return ToJsonString(ds.Tables[0]);
    }

    public static string  ToJsonString(this DataTable dataTable)
    {
        var strDc = new string[dataTable.Columns.Count];
        var headStr = string.Empty;
        if (dataTable.Rows.Count == 0)
        {
            return "";
        }
        for (var i = 0; i < dataTable.Columns.Count; i++)
        {
            strDc[i] = dataTable.Columns[i].Caption;
            headStr += "\"" + strDc[i] + "\" : \"" + strDc[i] + i + "¾" + "\",";
        }

        headStr = headStr.Substring(0, headStr.Length - 1);
        var builder = new StringBuilder();
        builder.Append("[");
        for (var i = 0; i < dataTable.Rows.Count; i++)
        {
            var tempStr = headStr;
            builder.Append("{");
            for (int j = 0; j < dataTable.Columns.Count; j++)
            {
                tempStr = tempStr.Replace(dataTable.Columns[j] + j.ToString() + "¾",
                                          dataTable.Rows[i][j].ToString());
            }
            builder.Append(tempStr + "},");
        }
        builder = new StringBuilder(builder.ToString().Substring(0, builder.ToString().Length - 1));
        builder.Append("]");
        return builder.ToString();
    }