从网站下载图像 .NET/C# [英] Download image from the site in .NET/C#

问题描述

我正在尝试从该站点下载图像.当图像可用时，我使用的代码运行良好.如果图像不可用，则会产生问题.如何验证图像的可用性?

I am trying to download images from the site. The code which I am using is working fine while the image is available. If the image it not available it is creating a problem. How to validate availability of the image?

代码:

方法一:

WebRequest requestPic = WebRequest.Create(imageUrl);

WebResponse responsePic = requestPic.GetResponse();

Image webImage = Image.FromStream(responsePic.GetResponseStream()); // Error

webImage.Save("D:\Images\Book\" + fileName + ".jpg");

方法二:

WebClient client = new WebClient();
Stream stream = client.OpenRead(imageUrl);

bitmap = new Bitmap(stream); // Error : Parameter is not valid.
stream.Flush();
stream.Close();
client.dispose();

if (bitmap != null)
{
    bitmap.Save("D:\Images\" + fileName + ".jpg");
}

Stream 有以下语句:

Stream has the following statements:

      Length  '((System.Net.ConnectStream)(str)).Length' threw an exception of type  'System.NotSupportedException'    long {System.NotSupportedException}
    Position  '((System.Net.ConnectStream)(str)).Position' threw an exception of type 'System.NotSupportedException'    long {System.NotSupportedException}
 ReadTimeout  300000    int
WriteTimeout  300000    int

推荐答案

无需涉及任何图像类，只需调用WebClient.DownloadFile:

There is no need to involve any image classes, you can simply call WebClient.DownloadFile:

string localFilename = @"c:localpath	ofile.jpg";
using(WebClient client = new WebClient())
{
    client.DownloadFile("http://www.example.com/image.jpg", localFilename);
}

<小时>

更新
由于您需要检查文件是否存在并下载文件，如果存在，最好在同一请求中执行此操作.所以这里有一个方法可以做到这一点:

---

Update
Since you will want to check whether the file exists and download the file if it does, it's better to do this within the same request. So here is a method that will do that:

private static void DownloadRemoteImageFile(string uri, string fileName)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();

    // Check that the remote file was found. The ContentType
    // check is performed since a request for a non-existent
    // image file might be redirected to a 404-page, which would
    // yield the StatusCode "OK", even though the image was not
    // found.
    if ((response.StatusCode == HttpStatusCode.OK || 
        response.StatusCode == HttpStatusCode.Moved || 
        response.StatusCode == HttpStatusCode.Redirect) &&
        response.ContentType.StartsWith("image",StringComparison.OrdinalIgnoreCase))
    {

        // if the remote file was found, download oit
        using (Stream inputStream = response.GetResponseStream())
        using (Stream outputStream = File.OpenWrite(fileName))
        {
            byte[] buffer = new byte[4096];
            int bytesRead;
            do
            {
                bytesRead = inputStream.Read(buffer, 0, buffer.Length);
                outputStream.Write(buffer, 0, bytesRead);
            } while (bytesRead != 0);
        }
    }
}

简而言之，它向文件发出请求，验证响应代码是OK、Moved 或Redirect 之一 并且 ContentType 是一个图像.如果这些条件为真，则下载文件.

In brief, it makes a request for the file, verifies that the response code is one of OK, Moved or Redirect and also that the ContentType is an image. If those conditions are true, the file is downloaded.

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