net直接下载文件

private void Down( string fileName)
{
//以字符流的形式下载文件
FileStream fs = new FileStream(Server.MapPath("/txt/" + fileName + ".txt"), FileMode.Open);
byte[] bytes = new byte[(int)fs.Length];
fs.Read(bytes, 0, bytes.Length);
fs.Close();
Response.ContentType = "application/octet-stream";
//通知浏览器下载文件而不是打开
Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName+".txt", System.Text.Encoding.UTF8));
Response.BinaryWrite(bytes);
Response.Flush();
Response.End();
}