protected void Page_Load(object sender, EventArgs e)        {string q = Request.QueryString.Get("q");

            System.IO.FileInfo f = new System.IO.FileInfo(Server.MapPath("/") + q);

int speed = 5000;//5K

            FileStream file = new FileStream(f.FullName, FileMode.Open, FileAccess.Read, FileShare.Read);            BinaryReader br = new BinaryReader(file);

            Response.AddHeader("Accept-Ranges", "bytes");

            Response.Buffer = false;long fileLength = file.Length;long startBytes = 0;

int buff = 10240; //每线程10K bytes

int sleep = 1000 * buff / speed;

if (Request.Headers["Range"] != null)            {                Response.StatusCode = 206;string[] range = Request.Headers["Range"].Split(new char[] { '=', '-' });

                startBytes = Convert.ToInt64(range[1]);            }

// 添加头信息，指定文件大小，让浏览器能够显示下载进度            Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());

if (startBytes != 0)            {                //支持多线程，文件分段处理                               Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));            }

//保持链接            Response.AddHeader("Connection", "Keep-Alive");

//设置输出流数据类型。添加头信息，为"文件下载/另存为"对话框指定默认文件名            Response.ContentType = "application/octet-stream";            Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(f.Name, System.Text.Encoding.UTF8));

//定义流的位置            br.BaseStream.Seek(startBytes, SeekOrigin.Begin);

long dataSent = fileLength - startBytes;long dataLeft = 0;

while (dataLeft < dataSent)            {if (Response.IsClientConnected)                {                    Response.BinaryWrite(br.ReadBytes(buff));                    dataLeft += buff;                    Response.Flush();                    Thread.Sleep(sleep);                }else                {                    dataSent = -1;                }            }            Response.End();            br.Close();            file.Close();        }