執行緒已終止

如果你的檔案下載程式，使用者反映每個文字檔的尾巴都會被塞一句「Error」，你會怎麼想？

「這一定是被駭客攻擊了...」

是的，我很想就這麼告訴使用者，但...我真的好心虛，於是，老老實實打開程式碼好好檢查一番。

Partial Class MainPage_FileDownloadSeal
    Inherits CommonPage

    Private Sub MainPage_FileDownloadSeal_Load(sender As Object, e As EventArgs) Handles Me.Load
        Dim wsfile As New AttachFileinfo()

        Try
            Dim FileID As String = Request("File").ToString().Trim()
            Dim ds_file As DataSet = wsfile.getFileBase(FileID)
            Dim strFilePath As String = ds_file.Tables(0).Rows(0)("檔案存放路徑").ToString() + ds_file.Tables(0).Rows(0)("系統檔名").ToString()
            Dim strFileName As String = ds_file.Tables(0).Rows(0)("使用者上傳檔名").ToString()



            If strFilePath.Length <> 0 Then
                If File.Exists(strFilePath) Then
                    If strFilePath.Length > 0 Then
                        Dim strSubName As String

                        strSubName = strFilePath.Substring(strFilePath.LastIndexOf(".") + 1, strFilePath.Length - strFilePath.LastIndexOf(".") - 1)

                        '"檔案分類"

                        Select Case strSubName.ToUpper()
                            Case "TXT"
                                Response.ContentType = "text/html"
                                Exit Select

                            Case "HTM"
                                Response.ContentType = "text/html"
                                Exit Select

                            Case "HTML"
                                Response.ContentType = "text/html"
                                Exit Select

                            Case "DOCX", "DOC"
                                Response.ContentType = "application/msword"
                                Exit Select

                            Case "XLS"
                                Response.ContentType = "application/vnd.ms-excel"
                                Exit Select

                            Case "GIF"
                                Response.ContentType = "image/gif"
                                Exit Select

                            Case "JPG"
                                Response.ContentType = "image/JPG"
                                Exit Select

                            Case "BMP"
                                Response.ContentType = "image/bmp"
                                Exit Select

                            Case "SWF"
                                Response.ContentType = "application/x-shockwave-flash"
                                Exit Select

                            Case "PDF"
                                Response.ContentType = "application/pdf"
                                Exit Select
                            Case Else
                                'specify that the response is a stream that cannot be read by the
                                'client and must be downloaded
                                Response.ContentType = "application/octet-stream"
                                Exit Select
                        End Select



                        Response.Clear()
                        '決定檔案存檔預設名稱
                        Response.AddHeader("Content-Disposition", "attachment;filename=" + Server.UrlEncode(strFileName))
                        Response.WriteFile(strFilePath)
                        Response.[End]()                        
                    End If
                End If
            End If
        Catch ex As Exception
            Response.Write("Error")
        End Try
    End Sub
End Class

這應該再普通不過了吧，別人有的我也有，別人沒加的，我還老實的都有加。你看看，那個 Try ... Catch ，就是我特別力求完整而補上的。

但重點是，別人沒錯，我錯了啊!?

在參考了「小筆記-避免 ThreadAbortException 的Response.End() 替代寫法」，其中一段說著：

Response.End() 會觸發 ThreadAbortException 造成中斷。若 Response.End() 被 try catch包覆，則會進入 catch 流程。

所以我的程式：

Try
    Response.Clear()
     '決定檔案存檔預設名稱
     Response.AddHeader("Content-Disposition", "attachment;filename=" + Server.UrlEncode(strFileName))
     Response.WriteFile(strFilePath)
     Response.[End]()     
Catch ex As Exception
    Response.Write("Error")
End Try

剛好把 Response.End() 放在 Try 裡頭，當他執行到 Response.End() 時，還沒來的及結束，就先去執行了 Catch 裡面的 Response.Writer("Error")

這也就解釋了，為何我的使用者所下載的檔案尾巴，都會留下一句：Error

所以，正確寫法應該是：

Try
    Response.Clear()
     '決定檔案存檔預設名稱
     Response.AddHeader("Content-Disposition", "attachment;filename=" + Server.UrlEncode(strFileName))
     Response.WriteFile(strFilePath)
Catch ex As Exception
    Response.Write("Error")
Finally
    Response.[End]()
End Try

把 Response.End() 放到 Finally 裡面