try
            {
                iStream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);
                long dataToRead = iStream.Length;
                HttpContext.Current.Response.ContentType = ContentType;
                //HttpContext.Current.Response.ClearHeaders();
                //HttpContext.Current.Response.AppendHeader("Cache-Control", "must-revalidate, post-check=0, pre-check=0");
                //HttpContext.Current.Response.AppendHeader("Pragma", "public");
                //HttpContext.Current.Response.AppendHeader("Cache-Control", "public");
                //HttpContext.Current.Response.Expires = 0;
                //HttpContext.Current.Response.CacheControl = "public";
                //HttpContext.Current.Response.Cache.SetExpires(DateTime.Now.AddMinutes(30));
                //HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.Public);

                //在IE下重编码fileName，在火狐下就不用了！
                if (Request.UserAgent.IndexOf("MSIE") > -1)
                {
                    HttpContext.Current.Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", this.Server.UrlPathEncode(fileName + ".xls"), Path.GetExtension(filePath)));

                }
                else
                {
                    HttpContext.Current.Response.AddHeader("Content-Disposition", string.Concat("attachment; filename=", fileName, Path.GetExtension(filePath)));
                }
                while (dataToRead > 0)
                {
                    if (HttpContext.Current.Response.IsClientConnected)
                    {                        
                        int length = iStream.Read(buffer, 0, buffersize);
                        HttpContext.Current.Response.OutputStream.Write(buffer, 0, length);
                        HttpContext.Current.Response.Flush();

                        buffer = new Byte[buffersize];
                        dataToRead = dataToRead - length;
                    }
                    else
                    {
                        dataToRead = -1;
                    }
                }
            }
            catch (Exception)
            {
                SetAlertMessage("文件下载时出现错误!");
            }