将指定excel文件中的数据转换成datatable对象，供应用程序进一步处理

   public DataTable ExportExcel(string sheetName)
{
DataTable rs = new DataTable();

            if (!this.FileUpload1.HasFile)
{

                this.RunInSide("请选择要导入的文件！");
return null;
}
try
{
//获取服务器路径
string upPath = Request.PhysicalApplicationPath + "BasisManage\\ExportExcel\\ExcelFolder\\" + DateTime.Now.ToString("yyyyMMddhhmmss") + ".xls";
FileUpload1.PostedFile.SaveAs(upPath);
OleDbConnection conn = new OleDbConnection("provider=microsoft.jet.oledb.4.0;" +
"data source=" + upPath + ";" +
"extended properties=\"excel 8.0;IMEX=1;\"");//很重要的（IMEX=1），缺少会导致部分数据读不出来
OleDbCommand myoledbcommand = new OleDbCommand("select * from [" + sheetName + "$]", conn);
OleDbDataAdapter mydata = new OleDbDataAdapter(myoledbcommand);
mydata.Fill(rs);

            }
catch (Exception ex)
{
this.RunInSide("格式不正确！请重新选择你要载入的文件！");
return null;
}
return rs;
}