ASP MVC 實作檔案下載功能

     

若要實作ASP MVC下載檔案的功能

需要先達成以下兩件事:

 1.指定Content-Type (告訴用戶端瀏覽器欲回應的內容)

string file = @"C:\Users\Administrator\Downloads\SQLEXPRADV_x64_ENU.exe";             string contentType = MimeMapping.GetMimeMapping(file);

 2. 指定Content-Disposition(告訴用戶端瀏覽器如何處理附加文件)

var cd = new System.Net.Mime.ContentDisposition             {                 FileName = "SQLEXPRADV_x64_ENU.exe ",                 Inline = false,              };        Response.AppendHeader("Content-Disposition", cd.ToString());

其中 Inline 設為 false 表示不要在瀏覽器上打開 

最後, 回傳 FileStreamResult

return File(                         new FileStream(file, FileMode.Open, FileAccess.Read)                          , contentType);

完整的程式碼如下:

public ActionResult Download()         {                         FileInfo fl = new FileInfo(@"C:\Users\Administrator\Downloads\SQLEXPRADV_x64_ENU.exe");                        var cd = new System.Net.Mime.ContentDisposition             {                 FileName = fl.Name,                 Inline = false,             };             Response.AppendHeader("Content-Disposition", cd.ToString());                          var readStream = new FileStream(fl.FullName, FileMode.Open, FileAccess.Read);             string contentType = MimeMapping.GetMimeMapping(fl.FullName);             return File(readStream, contentType);         }

若下載的檔案太大, 需要將Response.BufferOutput 設為false

不然由於IIS的限制,可能會讓我們遇到 Overflow or underflow in the arithmetic operation的錯訊息

public ActionResult LargeDownload()         {                         FileInfo fl = new FileInfo(@"C:\Users\Administrator\Downloads\SQLEXPRADV_x64_ENU.exe");                        var cd = new System.Net.Mime.ContentDisposition             {                 FileName = fl.Name,                 Inline = false,             };             Response.AppendHeader("Content-Disposition", cd.ToString());             Response.BufferOutput = false;             var readStream = new FileStream(fl.FullName, FileMode.Open, FileAccess.Read);             string contentType = MimeMapping.GetMimeMapping(fl.FullName);             return File(readStream, contentType);         }

補充:

Content-disposition:

指定用戶端瀏覽器如何處理附加文件

In a regular HTTP response, the Content-Disposition response header is a header indicating if the content is expected to be displayed inline in the browser, that is, as a Web page or as part of a Web page, or as an attachment, that is downloaded and saved locally.

REF:https://developer.mozilla.org/zh-TW/docs/Web/HTTP/Headers/Content-Disposition

常用的設定有

Content-Disposition: inline Content-Disposition: attachment Content-Disposition: attachment; filename="filename.jpg"

(Default 設定為inline, 就是直接在瀏覽器上打開)