using System.IO
void Download()
{
System.IO.FileStream r = new System.IO.FileStream(FileName, System.IO.FileMode.Open); //文件下载实例化
//设置基本信息
Response.Buffer= false;
Response.AddHeader("Connection", "Keep-Alive");
Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", "attachment;filename=" + System.IO.Path.GetFileName(FileName));
Response.AddHeader("Content-Length", r.Length.ToString());
while (true) //如果文件大于缓冲区，通过while循环多次加载文件
{
//开辟缓冲区空间
byte[] buffer = new byte[1024];
//读取文件的数据
int leng = r.Read(buffer, 0, 1024);
if(leng == 0) //到文件尾，结束
break;
if (leng == 1024) //读出的文件数据长度等于缓冲区长度，直接将缓冲区数据写入
Response.BinaryWrite(buffer); //向客户端发送数据流
else
{
//读出文件数据比缓冲区小，重新定义缓冲区大小，只用于读取文件的最后一个数据块
byte[] b = new byte[leng];
for (int i = 0; i < leng; i++)
b[i] = buffer[i];
Response.BinaryWrite(b);
}
}
r.Close();//关闭下载文件
Response.End();//结束文件下载
}