下载文件c#

public void getDown(string filename)    //文件名
    {
        string destFileName = Server.MapPath("~/") + filename;  //文件路径
        destFileName = Server.UrlDecode(destFileName);
        Response.Write(destFileName);
        if (File.Exists(destFileName))
        {
            FileInfo fi = new FileInfo(destFileName);
            Response.Clear();
            Response.ClearHeaders();
            Response.Buffer = false;
            Response.AppendHeader("Content-Disposition", "attachment;filename="
                + HttpUtility.UrlEncode(Path.GetFileName(destFileName), System.Text.Encoding.UTF8));
            Response.AppendHeader("Content-Length", fi.Length.ToString());
            Response.ContentType = "application/octet-stream";
            Response.WriteFile(destFileName);
            Response.Flush();
            Response.End();
        }
        else
        {
            Response.Write("<script langauge=javascript>alert('文件不存在!');history.go(-1);</script>");
            Response.End();
        }
    }