如何把datagrid中从数据库中显示的数据,导出到EXCEL中来报表呢?

/// <summary>
/// 将DataTable中的数据导出到指定的Excel文件中
/// </summary>
/// <param name="page">Web页面对象</param>
/// <param name="tab">包含被导出数据的DataTable对象</param>
/// <param name="FileName">Excel文件的名称</param>
public static void Export(System.Web.UI.Page page,System.Data.DataTable tab,string FileName)
{
System.Web.HttpResponse httpResponse = page.Response;
System.Web.UI.WebControls.DataGrid dataGrid=new System.Web.UI.WebControls.DataGrid();
dataGrid.DataSource=tab.DefaultView;
dataGrid.AllowPaging = false;
dataGrid.HeaderStyle.BackColor = System.Drawing.Color.Green;
dataGrid.HeaderStyle.HorizontalAlign = HorizontalAlign.Center;
dataGrid.HeaderStyle.Font.Bold = true;
dataGrid.DataBind();
httpResponse.AppendHeader("Content-Disposition","attachment;filename="+HttpUtility.UrlEncode(FileName,System.Text.Encoding.UTF8)); //filename="*.xls";
httpResponse.ContentEncoding=System.Text.Encoding.GetEncoding("GB2312");
httpResponse.ContentType ="application/ms-excel";
System.IO.StringWriter  tw = new System.IO.StringWriter() ;
System.Web.UI.HtmlTextWriter hw = new System.Web.UI.HtmlTextWriter (tw);
dataGrid.RenderControl(hw);

string filePath = page.Server.MapPath("..")+"\\Files\\" +FileName;
System.IO.StreamWriter sw = System.IO.File.CreateText(filePath);
sw.Write(tw.ToString());
sw.Close(); DownFile(httpResponse,FileName,filePath);

httpResponse.End();
}private static bool DownFile(System.Web.HttpResponse Response,string fileName,string fullPath)
{
try
{
Response.ContentType = "application/octet-stream";

Response.AppendHeader("Content-Disposition","attachment;filename=" + 
HttpUtility.UrlEncode(fileName,System.Text.Encoding.UTF8) + ";charset=GB2312");
System.IO.FileStream fs= System.IO.File.OpenRead(fullPath);
long fLen=fs.Length;
int size=102400;//每100K同时下载数据 
byte[] readData = new byte[size];//指定缓冲区的大小 
if(size>fLen)size=Convert.ToInt32(fLen);
long fPos=0;
bool isEnd=false;
while (!isEnd) 
{ 
if((fPos+size)>fLen)
{
size=Convert.ToInt32(fLen-fPos);
readData = new byte[size];
isEnd=true;
}
fs.Read(readData, 0, size);//读入一个压缩块 
Response.BinaryWrite(readData);
fPos+=size;
} 
fs.Close(); 
System.IO.File.Delete(fullPath);
return true;
}
catch
{
return false;
}
}