Question

我在使用WebClient类下载jpeg图像时遇到了一些问题。我试图通过以下代码下载jpeg图像：

public bool DownloadUri(string strUri, string destPath)
{
    bool result = false;
    try
    {
        Uri uri = new Uri(strUri, UriKind.RelativeOrAbsolute);
        WebClient client = new WebClient();
        client.DownloadFile(uri, destPath);
        result = true;
    }
    catch (Exception ex)
    {
        result = false;
    }
    return result;
}

大多数工作正常，虽然当jpeg不存在时，我试图下载重定向的网站并且下载不会引发异常，它会下载一个只有8k大小的损坏的jpeg。这是我提供的一个令人讨厌的网址：

http://axisproperty.net.au/Upload/listing/500748870/500748870_1_500266205%2c1336368187%2cImageA.jpg

我已经使用Uri.TryCreate和Uri.IsWellFormedUriString（urlAttribute.Value，UriKind.Absolute）验证了uri。我试过做一个File.Exists（uri.ToString（））来验证uri是否有一个与之关联的有效文件，尽管即使对于有效的url也是如此。

有没有其他方法来验证文件实际存在，所以我不下载所有这些不必要的损坏的jpeg文件？

Answer 1

httpcl重定向不由webclient.downloadfile方法处理

你应该使用webrequest

public static int DownloadFile(String remoteFilename, String localFilename)
    {
      // Function will return the number of bytes processed
      // to the caller. Initialize to 0 here.
      int bytesProcessed = 0;

      // Assign values to these objects here so that they can
      // be referenced in the finally block
      Stream remoteStream = null;
      Stream localStream = null;
      WebResponse response = null;

      // Use a try/catch/finally block as both the WebRequest and Stream
      // classes throw exceptions upon error
      try
      {
        // Create a request for the specified remote file name
        WebRequest request = WebRequest.Create(remoteFilename);
        if (request != null)
        {
          // Send the request to the server and retrieve the
          // WebResponse object 
          response = request.GetResponse();
          if (response != null)
          {
            // Once the WebResponse object has been retrieved,
            // get the stream object associated with the response's data
            remoteStream = response.GetResponseStream();

            // Create the local file
            localStream = File.Create(localFilename);

            // Allocate a 1k buffer
            byte[] buffer = new byte[1024];
            int bytesRead;

            // Simple do/while loop to read from stream until
            // no bytes are returned
            do
            {
              // Read data (up to 1k) from the stream
              bytesRead = remoteStream.Read(buffer, 0, buffer.Length);

              // Write the data to the local file
              localStream.Write(buffer, 0, bytesRead);

              // Increment total bytes processed
              bytesProcessed += bytesRead;
            } while (bytesRead > 0);
          }
        }
      }
      catch (Exception e)
      {
        Console.WriteLine(e.Message);
      }
      finally
      {
        // Close the response and streams objects here 
        // to make sure they're closed even if an exception
        // is thrown at some point
        if (response != null) response.Close();
        if (remoteStream != null) remoteStream.Close();
        if (localStream != null) localStream.Close();
      }

      // Return total bytes processed to caller.
      return bytesProcessed;
    }

Answer 2

对不起，我应该更清楚。我提供的网址无效，因此重定向到找不到网页或类似网页，因此我不想下载，因为该文件中没有有效的jpeg图片。我找到了以下解决方案：

public static bool CheckURL(string URL)
{
    try
    {
        HttpWebRequest req = (HttpWebRequest)WebRequest.Create(URL);
        req.UserAgent = "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)";
        using (HttpWebResponse rsp = (HttpWebResponse)req.GetResponse())
        {
            if ((rsp.StatusCode == HttpStatusCode.OK) && rsp.ContentType.ToLower() == "image/jpeg")
            {
                return true;
            }
        }
    }
    catch
    {
        return false;
    }
    return false;
}

WebClient DownloadFile为重定向的URI下载损坏的jpeg

2 个答案: