从URL - asp.net下载/流文件

Question

我需要流式传输一个文件，这将导致在浏览器中保存为提示。问题是，文件所在的目录是虚拟映射的，所以我无法使用Server.MapPath来确定它的实际位置。目录不在与网站相同的位置(甚至不在活动盒子上的物理服务器上)。

我希望如下所示，但这将允许我传递web URL，而不是服务器文件路径。

我可能最终必须从配置基本路径构建我的文件路径，然后附加到路径的其余部分，但希望我可以用这种方式来做。

var filePath = Server.MapPath(DOCUMENT_PATH);

if (!File.Exists(filePath))
    return;

var fileInfo = new System.IO.FileInfo(filePath);
Response.ContentType = "application/octet-stream";
Response.AddHeader("Content-Disposition", String.Format("attachment;filename=\"{0}\"", filePath));
Response.AddHeader("Content-Length", fileInfo.Length.ToString());
Response.WriteFile(filePath);
Response.End();

Answer 1

您可以使用HttpWebRequest获取文件并将其传输回客户端。这允许您使用url获取文件。我发现的一个这样的例子(但不记得从哪里得到信任)是

    //Create a stream for the file
    Stream stream = null;

    //This controls how many bytes to read at a time and send to the client
    int bytesToRead = 10000;

    // Buffer to read bytes in chunk size specified above
    byte[] buffer = new Byte[bytesToRead];

    // The number of bytes read
    try
    {
      //Create a WebRequest to get the file
      HttpWebRequest fileReq = (HttpWebRequest) HttpWebRequest.Create(url);

      //Create a response for this request
      HttpWebResponse fileResp = (HttpWebResponse) fileReq.GetResponse();

      if (fileReq.ContentLength > 0)
        fileResp.ContentLength = fileReq.ContentLength;

        //Get the Stream returned from the response
        stream = fileResp.GetResponseStream();

        // prepare the response to the client. resp is the client Response
        var resp = HttpContext.Current.Response;

        //Indicate the type of data being sent
        resp.ContentType = MediaTypeNames.Application.Octet;
    
        //Name the file 
        resp.AddHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
        resp.AddHeader("Content-Length", fileResp.ContentLength.ToString());
    
        int length;
        do
        {
            // Verify that the client is connected.
            if (resp.IsClientConnected)
            {
                // Read data into the buffer.
                length = stream.Read(buffer, 0, bytesToRead);

                // and write it out to the response's output stream
                resp.OutputStream.Write(buffer, 0, length);

                // Flush the data
                resp.Flush();

                //Clear the buffer
                buffer = new Byte[bytesToRead];
            }
            else
            {
                // cancel the download if client has disconnected
                length = -1;
            }
        } while (length > 0); //Repeat until no data is read
    }
    finally
    {
        if (stream != null)
        {
            //Close the input stream
            stream.Close();
        }
    }

Answer 2

将url下载为字节，并将字节转换为流：

using (var client = new WebClient())
{
    var content = client.DownloadData(url);
    using (var stream = new MemoryStream(content))
    {
        ...
    }
}   

Answer 3

我这样做了很多，我想我可以添加一个更简单的答案。我在这里将它设置为一个简单的类，但我每天晚上都会运行它来收集我关注的公司的财务数据。

class WebPage
{
    public static string Get(string uri)
    {
        string results = "N/A";

        try
        {
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(uri);
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

            StreamReader sr = new StreamReader(resp.GetResponseStream());
            results = sr.ReadToEnd();
            sr.Close();
        }
        catch (Exception ex)
        {
            results = ex.Message;
        }
        return results;
    }
}

在本例中，我传入了一个url，它以HTML的形式返回页面。如果你想对流做一些不同的事情，你可以很容易地改变它。

您可以这样使用它：

string page = WebPage.Get("http://finance.yahoo.com/q?s=yhoo");