• using System;
  using System.Data;
  using System.Configuration;
  using System.Web;
  using System.Web.Security;
  using System.Web.UI;
  using System.Web.UI.WebControls;
  using System.Web.UI.WebControls.WebParts;
  using System.Web.UI.HtmlControls;
  using System.IO;
   
  public partial class _Default : System.Web.UI.Page
  {
  protected void Page_Load(object sender, EventArgs e)
  {
   
  }
   
  //TransmitFile实现下载
  protected void Button1_Click(object sender, EventArgs e)
  {
  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)
  {
  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("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分块下载
  protected void Button3_Click(object sender, EventArgs e)
  {
  string fileName = "aaa.txt";//客户端保存的文件名
  string filePath = Server.MapPath("DownLoad/aaa.txt");//路径
   
  System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath);
   
  if (fileInfo.Exists == true)
  {
  const long ChunkSize = 102400;//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/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));//读取的大小
  Response.OutputStream.Write(buffer, 0, lengthRead);
  Response.Flush();
  dataLengthToRead = dataLengthToRead - lengthRead;
  }
  Response.Close();
  }
  }
   
  //流方式下载
  protected void Button4_Click(object sender, EventArgs e)
  {
  string fileName = "aaa.txt";//客户端保存的文件名
  string filePath = Server.MapPath("DownLoad/aaa.txt");//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();
   
  }
  }

转自：http://www.hello-code.com/blog/asp.net/201312/2414.html

C# 文件下载四方法