流方式下载文件

public ActionResult DownLoadAttachment(string attachmentId)
        {
            Attachment attachment = _customerInfoService.GetAttachment(attachmentId);
            if (attachment != null)
            {
                try
                {
                    string fileName = attachment.FileName;
                    string filePath = attachment.Path;
                    string fileType = attachment.FileType;
                    #region 流方式下载文件
                    Encoding encoding;
                    string outputFileName = null;
                    fileName = fileName.Replace("'", "");

                    string browser = Request.UserAgent.ToUpper();
                    if (browser.Contains("MS") == true && browser.Contains("IE") == true)
                    {
                        outputFileName = HttpUtility.UrlEncode(fileName);
                        encoding = Encoding.Default;
                    }
                    else if (browser.Contains("FIREFOX") == true)
                    {
                        outputFileName = fileName;
                        encoding = Encoding.GetEncoding("GB2312");
                    }
                    else
                    {
                        outputFileName = HttpUtility.UrlEncode(fileName);
                        encoding = Encoding.Default;
                    }
                    FileStream fs = new FileStream(filePath, FileMode.Open);
                    long length = fs.Length;
                    byte[] bytes = new byte[(int)fs.Length];
                    fs.Read(bytes, 0, bytes.Length);
                    fs.Close();
                    Response.Charset = "UTF-8";
                    Response.ContentType = "application/octet-stream";
                    Response.ContentEncoding = encoding;
                    Response.AddHeader("Content-Disposition", "attachment; filename=" + outputFileName);
                    Response.BinaryWrite(bytes);
                    Response.Flush();
                    Response.End();
                    return new EmptyResult();
                    #endregion
                }
                catch (Exception ex)
                {
                    return Content(string.Format("附件下载失败！错误信息:{0}", ex.Message));
                }

            }
            else
            {
                return Content("附件不存在！");
            }
        }

ASP.NET Core 中的fileresult对象

[HttpGet("DownLoadAttachment")]
        public FileResult DownLoadAttachment(string attachmentId)
        {
            Attachment attachment = _customerInfoService.GetAttachment(attachmentId);
            string fileName = attachment.FileName;
            string filePath = attachment.Path;
            string fileType = attachment.FileType;
            if (!System.IO.File.Exists(filePath)) return null;

            var stream = System.IO.File.OpenRead(filePath);  //创建文件流

            return File(stream, fileType, fileName);
        }