ASP.NET檔案下載 
//TransmitFile實現下載    protected void Button1_Click(object sender, EventArgs e)
    {
        /*
         微軟為Response物件提供了一個新的方法TransmitFile來解決使用Response.BinaryWrite
         下載超過400mb的檔案時導致Aspnet_wp.exe程序回收而無法成功下載的問題。
         程式碼如下：
         */

        Response.ContentType = "application/x-zip-compressed
 
";
        Response.AddHeader("Content-Disposition", "attachment;filename=z.zip");
        string filename = Server.MapPath("DownLoad/z.zip");
        Response.TransmitFile(filename);
    }

    //WriteFile實現下載    protected void Button2_Click(object sender, EventArgs e)
    {
        /*
         using System.IO;
         
         
 
*/

        string fileName = "asd.txt";//客戶端儲存的檔名        string filePath = Server.MapPath("DownLoad/aaa.txt");//路徑
        FileInfo fileInfo = new FileInfo(filePath);
        Response.Clear();
        Response.ClearContent();
        Response.ClearHeaders();
        Response.AddHeader("Content-Disposition
 
", "attachment;filename=" + fileName);
        Response.AddHeader("Content-Length", fileInfo.Length.ToString());
        Response.AddHeader("Content-Transfer-Encoding", "binary");
        Response.ContentType = "application/octet-stream";
        Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
        Response.WriteFile(fileInfo.FullName);
        Response.Flush();
        Response.End();
    }

    //WriteFile分塊下載    protected void Button3_Click(object sender, EventArgs e)
    {

        string fileName = "aaa.txt";//客戶端儲存的檔名        string filePath = Server.MapPath("DownLoad/aaa.txt");//路徑
        System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);

        if (fileInfo.Exists == true)
        {
            const long ChunkSize = 102400;//100K 每次讀取檔案，只讀取100Ｋ，這樣可以緩解伺服器的壓力            byte[] buffer = new byte[ChunkSize];

            Response.Clear();
            System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);
            long dataLengthToRead = iStream.Length;//獲取下載的檔案總大小            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName));
            while (dataLengthToRead > 0 && Response.IsClientConnected)
            {
                int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//讀取的大小                Response.OutputStream.Write(buffer, 0, lengthRead);
                Response.Flush();
                dataLengthToRead = dataLengthToRead - lengthRead;
            }
            Response.Close();
        }
    }

    //流方式下載    protected void Button4_Click(object sender, EventArgs e)
    {
        string fileName = "aaa.txt";//客戶端儲存的檔名        string filePath = Server.MapPath("DownLoad/aaa.txt");//路徑

        //以字元流的形式下載檔案        FileStream fs = new FileStream(filePath, FileMode.Open);
        byte[] bytes = new byte[(int)fs.Length];
        fs.Read(bytes, 0, bytes.Length);
        fs.Close();
        Response.ContentType = "application/octet-stream";
        //通知瀏覽器下載檔案而不是開啟        Response.AddHeader("Content-Disposition", "attachment;  filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));
        Response.BinaryWrite(bytes);
        Response.Flush();
        Response.End();

    }