asp.net中大文件下载

        public void download()
        {
            System.IO.Stream iStream = null;

            byte[] buffer = new Byte[10000];//设置大小
            int length;
            long dataToRead;
            string filepath = Server.MapPath("~/Upload/XXX/YYY.rar");//文件的路径
            string filename = System.IO.Path.GetFileName(filepath);

            try
            {
                iStream = new System.IO.FileStream(filepath, FileMode.Open, FileAccess.Read);
                dataToRead = iStream.Length;

                Response.Clear();
                Response.ClearHeaders();
                Response.ClearContent();
                Response.ContentType = "application/unknow"; 
                Response.AddHeader("Content-Length", dataToRead.ToString());
                Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);

                while (dataToRead > 0)
                {
                    if (Response.IsClientConnected)
                    {
                        length = iStream.Read(buffer, 0, 10000);
                        Response.OutputStream.Write(buffer, 0, length);
                        Response.Flush();

                        buffer = new Byte[10000];
                        dataToRead = dataToRead - length;
                    }
                    else
                    {
                        dataToRead = -1;
                    }
                }
            }
            catch (Exception ex)
            {
                Response.Write("Error : " + ex.Message);
            }
            finally
            {
                if (iStream != null)
                {
                    iStream.Close();
                }

                Response.End();
            }
        }