在ASP.NET中下载文件

//TransmitFile实现下载
    protected void Button1_Click(object sender, EventArgs e)
    {
        /*
        微软为Response对象提供了一个新的方法TransmitFile来解决使用Response.BinaryWrite
        下载超过400mb的文件时导致Aspnet_wp.exe进程回收而无法成功下载的问题。
        代码如下：
        */
        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实现下载
    protected void Button2_Click(object sender, EventArgs e)
    {
        /*
        using System.IO;
        */
        string fileName = "asd.txt";//客户端保存的文件名
        string filePath = Server.MapPath("DownLoad/aaa.txt");//路径
        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("