從DataTable導出Excel文件

/// <summary>
        /// 導出記錄
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Button1_Click(object sender, EventArgs e)
        {
            string sql = "select c.UserID as '用戶名',a.UserName as '姓名',b.SchoolName as '學校',b.ZhuanYe as '專業',c.Sdate as '訪問日期',c.CallPage as '頁面地址',a.Email as '用戶郵箱',a.Telephone as '用戶聯繫號碼' from XTGL_UserVisitDetails as c left join XTGL_UserInfo as a on c.UserID=a.UserID left join Student_Info as b on c.UserID=b.UserID 
            DataTable dt = DataAccess.GetDataTable(sql);
            string path = PubMethod.GetPath("70");//服務器的文件路徑
            try
            {
                ExportExcelStream(dt, HttpUtility.HtmlDecode(path + "用戶訪問明細.xls"));

                PubMethod.DownloadFile(Page, "用戶訪問明細", path + "用戶訪問明細.xls", ".xls");
            }
            catch (Exception)
            {
                PubMethod.ShowMessage(Page, "數據導出出錯");
            }

        }

        /// <summary>
        /// 保存DataTable數據到filepath文件中
        /// </summary>
        /// <param name="table">數據源</param>
        /// <param name="filepath">文件</param>
        public void ExportExcelStream(DataTable table, string filepath)
        {
            StringWriter stringWriter = new StringWriter();
            HtmlTextWriter htmlWriter = new HtmlTextWriter(stringWriter);
            System.Web.UI.WebControls.DataGrid excel = new System.Web.UI.WebControls.DataGrid();
            excel.DataSource = table.DefaultView;  //輸出DataTable的內容 
            excel.DataBind();
            excel.RenderControl(htmlWriter);

            string filestr = filepath;
            int pos = filestr.LastIndexOf("//");
            string file = filestr.Substring(0, pos);
            if (!Directory.Exists(file))
            {
                Directory.CreateDirectory(file);
            }
            System.IO.StreamWriter sw = new StreamWriter(filestr);
            try
            {
                sw.Write(stringWriter.ToString());
            }
            catch (Exception)
            {
                PubMethod.ShowMessage(Page, "數據導出出錯");
            }

            sw.Close();
        }