从网页创建和下载文本文件

引言

在 Web 应用程序中，通常需要将某种文件下载到客户端计算机的功能。本文将说明如何创建并将文本文件下载到用户的计算机。

使用代码

虽然在示例中，我实际上在将文本文件流式传输到客户端之前创建它，但我认为强调一下，你并不一定需要这样做，因为该文件实际上可能存在于文件系统中，并且你可能希望将其流式传输到客户端。如果是这样，你可能需要使用 FileStream 来读取已经存在的文档。

我们首先打开文件进行读取，并实际逐字节将文件读取到流中，然后一旦将文件放入流中，我们只需使用 Response 对象并通过输出流下载文件。

Response.AddHeader("Content-disposition", "attachment; filename=" + sGenName);
Response.ContentType = "application/octet-stream";
Response.BinaryWrite(btFile);
Response.End();

此代码片段的真正威力在于上面的几行代码；通过添加一个标头，你告诉浏览器将文件作为附件下载。然后你设置 ContentType 标头，该标头被添加，并设置你的 MIME 类型，以便浏览器知道它即将下载哪种类型的文件。你可以为浏览器选择以下任何 MIME 类型

".asf" = "video/x-ms-asf"
".avi" = "video/avi"
".doc" = "application/msword"
".zip" = "application/zip"
".xls" = "application/vnd.ms-excel"
".gif" = "image/gif"
".jpg"= "image/jpeg"
".wav" = "audio/wav"
".mp3" = "audio/mpeg3"
".mpg" "mpeg" = "video/mpeg"
".rtf" = "application/rtf"
".htm", "html" = "text/html"
".asp" = "text/asp"
 
'Handle All Other Files
= "application/octet-stream"

下载文本文件的完整示例代码如下

protected void Button1_Click(object sender, EventArgs e)
{
    string sFileName = System.IO.Path.GetRandomFileName();
    string sGenName = "Friendly.txt";

    //YOu could omit these lines here as you may
    //not want to save the textfile to the server
    //I have just left them here to demonstrate that you could create the text file 
    using (System.IO.StreamWriter SW = new System.IO.StreamWriter(
           Server.MapPath("TextFiles/" + sFileName + ".txt")))
    {
        SW.WriteLine(txtText.Text);
        SW.Close();
    }

    System.IO.FileStream fs = null;
    fs = System.IO.File.Open(Server.MapPath("TextFiles/" + 
             sFileName + ".txt"), System.IO.FileMode.Open);
    byte[] btFile = new byte[fs.Length];
    fs.Read(btFile, 0, Convert.ToInt32(fs.Length));
    fs.Close();
    Response.AddHeader("Content-disposition", "attachment; filename=" + 
                       sGenName);
    Response.ContentType = "application/octet-stream";
    Response.BinaryWrite(btFile);
    Response.End();
}

Dim strFileName As String = System.IO.Path.GetRandomFileName()
Dim strFriendlyName As String = "Friendly.txt"

Using sw As New System.IO.StreamWriter(Server.MapPath(_
      "TextFiles/" + strFileName + ".txt"))
    sw.WriteLine(txtText.Text)
    sw.Close()
End Using

Dim fs As System.IO.FileStream = Nothing


fs = System.IO.File.Open(Server.MapPath("TextFiles/" + strFileName + _
     ".txt"), System.IO.FileMode.Open)
Dim btFile(fs.Length) As Byte
fs.Read(btFile, 0, fs.Length)
fs.Close()
With Response
    .AddHeader("Content-disposition", "attachment;filename=" & strFriendlyName)
    .ContentType = "application/octet-stream"
   .BinaryWrite(btFile)
    .End()
end with

结论

使用这种方法，你应该能够在 Windows 系统上下载所有类型的文件，但 Macintosh 系统存在一些问题。具体来说，你可能无法下载文件，而是它们将像预期一样在浏览器中打开。

参考文献

• 下载和上传文件
• 将附件发送到浏览器