使用 httpHandler(.ashx) 从特定位置下载文件

在 ASP.NET 项目中创建一个新的 httpHandler。将以下代码(VB)应用于处理程序文件:

Public Class AttachmentDownload
    Implements System.Web.IHttpHandler

    Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest

        ' pass an ID through the query string to append a unique identifer to your downloadable fileName

        Dim fileUniqueId As Integer = CInt(context.Request.QueryString("id"))

        ' file path could also be something like "C:\FolderName\FilesForUserToDownload

        Dim filePath As String = "\\ServerName\FolderName\FilesForUserToDownload"
        Dim fileName As String = "UserWillDownloadThisFile_" & fileUniqueId
        Dim fullFilePath = filePath & "\" & fileName
        Dim byteArray() As Byte = File.ReadAllBytes(fullFilePath)

        ' promt the user to download the file

        context.Response.Clear()
        context.Response.ContentType = "application/x-please-download-me" ' "application/x-unknown"
        context.Response.AppendHeader("Content-Disposition", "attachment; filename=" & fileName)
        context.Response.BinaryWrite(byteArray)
        context.Response.Flush()
        context.Response.Close()
        byteArray = Nothing

    End Sub

    ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
        Get
            Return False
        End Get
    End Property

End Class

你可以从后面的代码或客户端语言调用处理程序。在这个例子中,我使用的是一个调用处理程序的 javascript。

function openAttachmentDownloadHandler(fileId) {

    // the location of your handler, and query strings to be passed to it

    var url = "..\\_Handlers\\AttachmentDownload.ashx?";
    url = url + "id=" + fileId;

    // opening the handler will run its code, and it will close automatically
    // when it is finished. 

    window.open(url);

} 

现在附加将 javascript 函数分配给 Web 表单中可单击元素上的按钮单击事件。例如:

<asp:LinkButton ID="lbtnDownloadFile" runat="server" OnClientClick="openAttachmentDownloadHandler(20);">Download A File</asp:LinkButton>

或者你也可以从后面的代码中调用 javascript 函数:

ScriptManager.RegisterStartupScript(Page,
                Page.GetType(),
                "openAttachmentDownloadHandler",
                "openAttachmentDownloadHandler(" & fileId & ");",
                True)

现在,当你单击按钮时,httpHandler 会将你的文件发送到浏览器并询问用户是否要下载它。