c# Sample code sharing for exporting Datatable data to Excel table

public FileResult GetExcelFile()
    {
      if (Session["beginDate"] != null)
      {
        string bdate = Session["beginDate"].ToString();
        DateTime ld = Convert.ToDateTime(Session["lastDate"].ToString());
        DateTime ldate = ld.AddDays(1);
        string lldate = ldate.ToString("yyyy-MM-dd");
        int ptkey = Convert.ToInt32(Session["Process_PTR"]);
        string proceSql = "select * from Assay_Process where RKEY="+ptkey;
        DataTable proceDt = SqlHelper.QueryTable(proceSql);
        IDataParameter[] iDataTitle = new SqlParameter[3];
        iDataTitle[0] = new SqlParameter("@BeginDate", bdate);
        iDataTitle[1] = new SqlParameter("@LastDate", lldate);
        iDataTitle[2] = new SqlParameter("@RKEY", ptkey);
        DataSet dtTitle = SqlHelper.RunProceduresByParameter("pro_GetAssalyInfoByExportPrint", iDataTitle);
        DataTable dt = dtTitle.Tables[0];
        string outStr = ExcelExport.outExcel(dt);
        byte[] fileContents = Encoding.UTF8.GetBytes(outStr.ToString());
        return File(fileContents, "application/ms-excel", "" + proceDt.Rows[0]["ProcessName"]
        .ToString().Trim() + "化验单据(" + bdate.Trim() + "-" + lldate.Trim() + ").xls"); 
      }
      else
      {
        string qua_no = Session["quano"].ToString();
        IDataParameter[] iDataTitle = new SqlParameter[1];
        iDataTitle[0] = new SqlParameter("@Qua_no", qua_no);
        DataSet dtTitle = SqlHelper.RunProceduresByParameter("pro_GetAssalyInfoByQua_No", iDataTitle);
        DataTable dt = dtTitle.Tables[0];
        string outStr = ExcelExport.outExcel(dt);
        byte[] fileContents = Encoding.UTF8.GetBytes(outStr.ToString());
        return File(fileContents, "application/ms-excel", "化验单据(" + qua_no.Trim()+ ").xls"); 
      }
    }