原创：ASP.NET把DataTable转成XML文件的函数(DataSet转XML也可以)

        protected void Page_Load(object sender, EventArgs e)
        {
            //通过数据访问层把position读取到Datatable
            BizRules.PersonnelDAL pl = new PersonnelDAL();
            DataTable dt = pl.Getposition();
            StringBuilder str = new StringBuilder();
            str.Append(DataTableToXml(dt));
            this.CreateXml(str.ToString(), "test.xml");
            Response.Write("生成test.xml成功");
        }

        /// <summary>
        /// 生成文件
        /// </summary>
        /// <param name="val"></param>
        /// <param name="filename"></param>
        public void CreateXml(string val, string filename)
        {
            UnicodeEncoding ucode = new UnicodeEncoding();
            StreamWriter sw = new StreamWriter(Server.MapPath(filename));
            sw.WriteLine("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
            sw.WriteLine(val);
            sw.Close();
            sw.Dispose();
        }

        /// <summary>
        /// 转换成XML格式字符串
        /// </summary>
        /// <param name="dt"></param>
        /// <returns></returns>
        public string DataTableToXml(DataTable dt)
        {
            StringBuilder strXml = new StringBuilder();
            strXml.AppendLine("<XmlTable>");
            for (int i = 0; i < dt.Rows.Count; i  )
            {
                strXml.AppendLine("    <rows>");
                for (int j = 0; j < dt.Columns.Count; j  )
                {
                    strXml.AppendLine("        <"   dt.Columns[j].ColumnName   ">"   dt.Rows[i][j]   "</"   dt.Columns[j].ColumnName   ">");
                }
                strXml.AppendLine("    </rows>");
            }
            strXml.AppendLine("</XmlTable>");
            return strXml.ToString();
        }