C# 从.NET/C中的站点下载图像#

我正在尝试从网站下载图片。我使用的代码在图像可用时工作正常。如果图像不可用，则会产生问题。如何验证映像的可用性

代码：

方法1：

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2：

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");
}

编辑：

流具有以下语句：

      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

---

无需涉及任何图像类，您只需调用：

---

更新
由于您需要检查文件是否存在，如果存在，则下载文件，因此最好在相同的请求中执行此操作。这里有一个方法可以做到这一点：

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，它请求文件，验证响应代码是否为

OK

、

Moved

或

Redirect

之一，以及

ContentType

是否为图像。如果这些条件为真，则下载该文件。

我在一个项目中使用了上面Fredrik的代码，并做了一些轻微的修改，我想与大家分享一下：

private static bool DownloadRemoteImageFile(string uri, string fileName)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
    HttpWebResponse response;
    try
    {
        response = (HttpWebResponse)request.GetResponse();
    }
    catch (Exception)
    {
        return false;
    }

    // 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 it
        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);
        }
        return true;
    }
    else
        return false;
}

主要变化是：

• 对GetResponse（）使用try/catch，因为当远程文件返回404时，我遇到了一个异常
• 返回布尔值

---

也可以使用下载数据方法

    private byte[] GetImage(string iconPath)
    {
        using (WebClient client = new WebClient())
        {
            byte[] pic = client.DownloadData(iconPath);
            //string checkPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments) +@"\1.png";
            //File.WriteAllBytes(checkPath, pic);
            return pic;
        }
    }

---

从服务器或网站下载图像并在本地存储的最佳实践

WebClient client=new Webclient();
client.DownloadFile("WebSite URL","C:\\....image.jpg");
client.Dispose();

您可以使用此代码

using (WebClient client = new WebClient()) {
                    Stream stream = client.OpenRead(imgUrl);
                    if (stream != null) {
                        Bitmap bitmap = new Bitmap(stream);
                        ImageFormat imageFormat = ImageFormat.Jpeg;
                        if (bitmap.RawFormat.Equals(ImageFormat.Png)) {
                            imageFormat = ImageFormat.Png;
                        }
                        else if (bitmap.RawFormat.Equals(ImageFormat.Bmp)) {
                            imageFormat = ImageFormat.Bmp;
                        }
                        else if (bitmap.RawFormat.Equals(ImageFormat.Gif)) {
                            imageFormat = ImageFormat.Gif;
                        }
                        else if (bitmap.RawFormat.Equals(ImageFormat.Tiff)) {
                            imageFormat = ImageFormat.Tiff;
                        }

                        bitmap.Save(fileName, imageFormat);
                        stream.Flush();
                        stream.Close();
                        client.Dispose();
                    }
                }

---

项目位于：
别忘了处理

网络客户端

@Geetha：如果您尝试在web浏览器中导航到给定的URL，是否会获得图像？@Geetha：听起来好像您首先要检查图像是否存在，然后下载它。对于第一步，检查这里：它花费了太多的时间，而且下载空白图像。线位图=新位图（流）；显示错误：参数无效“不需要涉及任何图像类”。实际上，如果你的目的是下载一个图像，对它进行操作，然后简单地显示它，这是有必要的。如果不需要存储文件，则不需要存储文件，甚至不需要在磁盘中填充图像。请使用

try-catch

将有问题的语句包装起来，并向我们提供异常详细信息。行位图=新位图（流）；显示错误：参数无效。谢谢-看起来像是编写良好的代码，在我的应用程序中运行良好。当可以引发异常时，为什么要返回布尔标志？在性能出现问题之前，它总是更好的。SRP不允许有这些方法。也许您可以解释一下这段代码，以及它为什么工作？

WebClient client=new Webclient();
client.DownloadFile("WebSite URL","C:\\....image.jpg");
client.Dispose();

using (WebClient client = new WebClient()) {
                    Stream stream = client.OpenRead(imgUrl);
                    if (stream != null) {
                        Bitmap bitmap = new Bitmap(stream);
                        ImageFormat imageFormat = ImageFormat.Jpeg;
                        if (bitmap.RawFormat.Equals(ImageFormat.Png)) {
                            imageFormat = ImageFormat.Png;
                        }
                        else if (bitmap.RawFormat.Equals(ImageFormat.Bmp)) {
                            imageFormat = ImageFormat.Bmp;
                        }
                        else if (bitmap.RawFormat.Equals(ImageFormat.Gif)) {
                            imageFormat = ImageFormat.Gif;
                        }
                        else if (bitmap.RawFormat.Equals(ImageFormat.Tiff)) {
                            imageFormat = ImageFormat.Tiff;
                        }

                        bitmap.Save(fileName, imageFormat);
                        stream.Flush();
                        stream.Close();
                        client.Dispose();
                    }
                }