需求：下载站点目录下DownLoad文件夹中的logo.zip

前端HTML代码部分：

<div>
            1.通过超链接下载：<a href="../DownLoadFiles/logo.zip">点击下载</a><br />
            <!-- 一样的效果 -->
            1.通过超链接下载：<a href="/DownLoadFiles/logo.zip">点击下载</a><br />
            2.通过Response对象的TransmitFile方法（这个方法下载下来的是整个网页：DownLoadFile.aspx）：<asp:Button runat="server" ID="btnDownload" Text="点击下载" OnClick="btnDownload_Click" /><br />
            3.WriteFile实现下载：<asp:Button runat="server" ID="btnDownload2" Text="点击下载" OnClick="btnDownload_Click2" /><br />
            4.WriteFile分块下载：<asp:Button runat="server" ID="btnDownload3" Text="点击下载" OnClick="btnDownload_Click3" /><br />
            5.字符流方式下载文件：<asp:Button runat="server" ID="btnDownload4" Text="点击下载" OnClick="btnDownload_Click4" />
        </div>

后端类部分：

第一种方法：

超链接的形式下载：html代码中已实现

第二种方法：

 protected void btnDownload_Click(object sender, EventArgs e)
    {
        //这种方法会把整个网页下载下来
        //TransmitFile实现下载
        /*
        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：
          */

        //文件下载，所以文件头也含有zip
        Response.ContentType = "application/x-zip-compressed";
        Response.AddHeader("Content-Disposition", "attachment:filename=logo.zip");
        //找到文件的绝对路径
        string filename = Server.MapPath(".") + "/DownLoadFiles/logo.zip";
        Response.TransmitFile(filename);

    }

第三种方法：

protected void btnDownload_Click2(object sender, EventArgs e)
    {
        //WriteFile实现下载
        string fileName = "logo.zip";//客户端保存的文件名
        string filePath = Server.MapPath(".") + "/DownLoadFiles/logo.zip";//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("Content-Transfer-Encoding", "binary");
        Response.ContentType = "application/octet-stream";
        Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");
        Response.WriteFile(fileInfo.FullName);
        Response.Flush();
        Response.End();
    }

第四种方法：

 protected void btnDownload_Click3(object sender, EventArgs e)
    {
        //WriteFile分块下载
        string fileName = "logo.zip";//客户端保存的文件名
        string filePath = Server.MapPath(".") + "/DownLoadFiles/logo.zip";//路径
        System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);
        if (fileInfo.Exists == true)
        {
            const long ChunkSize = 409600;//100K 每次读取文件，只读取100Ｋ，这样可以缓解服务器的压力
            byte[] buffer = new byte[ChunkSize];
            Response.Clear();
            System.IO.FileStream iStream = System.IO.File.OpenRead(filePath);
            long dataLengthToRead = iStream.Length;//获取下载的文件总大小
            //Response.ContentType = "application/x-zip-compressed";      //可以改成zip哦
            Response.ContentType = "application/octet-stream";   //也可以不改哦
            Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName));
            while (dataLengthToRead > 0 && Response.IsClientConnected)
            {
                int lengthRead = iStream.Read(buffer, 0, Convert.ToInt32(ChunkSize));//读取的大小
                Response.OutputStream.Write(buffer, 0, lengthRead);
                Response.Flush();
                dataLengthToRead = dataLengthToRead - lengthRead;
            }
            Response.Close();
        }
    }

第五种方法：

  protected void btnDownload_Click4(object sender, EventArgs e)
    {
        //字符流方式下载文件
        string fileName = "logo.zip";//客户端保存的文件名
        string filePath = Server.MapPath(".") + "/DownLoadFiles/logo.zip";//路径

        //以字符流的形式下载文件
        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";
       //通知浏览器下载文件而不是打开
        Response.AddHeader("Content-Disposition", "attachment;   filename=" + HttpUtility.UrlEncode(fileName, System.Text.Encoding.UTF8));
         Response.BinaryWrite(bytes);
         Response.Flush();
         Response.End();
    }
}

注意：如果出现无法进行下载，提示logo.zip被另一个文件占用的时候，可以直接关闭项目，再重启项目。问题就会得到解决。
参考链接：https://blog.csdn.net/llftc/article/details/7099753