C# 如何使用 httpwebrequest 将图像从网站拉到本地文件

How to use httpwebrequest to pull image from website to local file

提问by Steve Brownell

I'm trying to use a local c# app to pull some images off a website to files on my local machine. I'm using the code listed below. I've tried both ASCII encoding and UTF8 encoding but the final file is not an correct. Does anyone see what I'm doing wrong? The url is active and correct and show the image just fine when I put the address in my browser.

我正在尝试使用本地 c# 应用程序将一些图像从网站上提取到本地计算机上的文件中。我正在使用下面列出的代码。我尝试了 ASCII 编码和 UTF8 编码，但最终文件不正确。有没有人看到我做错了什么？当我将地址放入浏览器时，该 url 处于活动状态且正确无误，并且可以很好地显示图像。

    private void button1_Click(object sender, EventArgs e)
    {
        HttpWebRequest lxRequest = (HttpWebRequest)WebRequest.Create("http://www.productimageswebsite.com/images/stock_jpgs/34891.jpg");

        // returned values are returned as a stream, then read into a string
        String lsResponse = string.Empty;
        HttpWebResponse lxResponse = (HttpWebResponse)lxRequest.GetResponse();
        using (StreamReader lxResponseStream = new StreamReader(lxResponse.GetResponseStream()))
        {
            lsResponse = lxResponseStream.ReadToEnd();
            lxResponseStream.Close();
        }

        byte[] lnByte = System.Text.UTF8Encoding.UTF8.GetBytes(lsResponse);

        System.IO.FileStream lxFS = new FileStream("34891.jpg", FileMode.Create);
        lxFS.Write(lnByte, 0, lnByte.Length);
        lxFS.Close();

        MessageBox.Show("done");
    }

采纳答案by Phil Rykoff

nice image :D

好图 :D

try using the following code:

尝试使用以下代码：

you needed to use a BinaryReader, 'cause an image file is binary data and thus not encoded in UTF or ASCII

您需要使用 BinaryReader，因为图像文件是二进制数据，因此不是以 UTF 或 ASCII 编码

edit: using'ified

编辑：使用'化

HttpWebRequest lxRequest = (HttpWebRequest)WebRequest.Create(
"http://www.productimageswebsite.com/images/stock_jpgs/34891.jpg");

// returned values are returned as a stream, then read into a string
String lsResponse = string.Empty;
using (HttpWebResponse lxResponse = (HttpWebResponse)lxRequest.GetResponse()){
   using (BinaryReader reader = new BinaryReader(lxResponse.GetResponseStream())) {
      Byte[] lnByte = reader.ReadBytes(1 * 1024 * 1024 * 10);
      using (FileStream lxFS = new FileStream("34891.jpg", FileMode.Create)) {
          lxFS.Write(lnByte, 0, lnByte.Length);
      }
   }
}
MessageBox.Show("done");

回答by Steve Brownell

Okay, here's the final answer. It uses a memorystream as a way to buffer the data from the reaponsestream.

好的，这是最终答案。它使用内存流作为缓冲来自响应流的数据的一种方式。

    private void button1_Click(object sender, EventArgs e)
    {
        byte[] lnBuffer;
        byte[] lnFile;

        HttpWebRequest lxRequest = (HttpWebRequest)WebRequest.Create("http://www.productimageswebsite.com/images/stock_jpgs/34891.jpg");
        using (HttpWebResponse lxResponse = (HttpWebResponse)lxRequest.GetResponse())
        {
            using (BinaryReader lxBR = new BinaryReader(lxResponse.GetResponseStream()))
            {
                using (MemoryStream lxMS = new MemoryStream())
                {
                    lnBuffer = lxBR.ReadBytes(1024);
                    while (lnBuffer.Length > 0)
                    {
                        lxMS.Write(lnBuffer, 0, lnBuffer.Length);
                        lnBuffer = lxBR.ReadBytes(1024);
                    }
                    lnFile = new byte[(int)lxMS.Length];
                    lxMS.Position = 0;
                    lxMS.Read(lnFile, 0, lnFile.Length);
                }
            }
        }

        using (System.IO.FileStream lxFS = new FileStream("34891.jpg", FileMode.Create))
        {
            lxFS.Write(lnFile, 0, lnFile.Length);
        }
        MessageBox.Show("done");
    }

回答by Learner

A variation of the answer, using async await for async file I/O. See Async File I/Oon why this is important.

答案的变体，使用async await 进行异步文件 I/O。请参阅异步文件 I/O了解为什么这很重要。

Download png and write to disk using BinaryReader/Writer

使用 BinaryReader/Writer 下载 png 并写入磁盘

string outFile = System.IO.Path.Combine(outDir, fileName);

// Download file
var request = (HttpWebRequest) WebRequest.Create(imageUrl);

using (var response = await request.GetResponseAsync()){
    using (var reader = new BinaryReader(response.GetResponseStream())) {

        // Read file 
        Byte[] bytes = async reader.ReadAllBytes();

        // Write to local folder 
        using (var fs = new FileStream(outFile, FileMode.Create)) {
            await fs.WriteAsync(bytes, 0, bytes.Length);
        }
    }
}

Read all bytes extension method

读取所有字节扩展方法

public static class Extensions {

    public static async Task<byte[]> ReadAllBytes(this BinaryReader reader)
    {
        const int bufferSize = 4096;
        using (var ms = new MemoryStream())
        {
            byte[] buffer = new byte[bufferSize];
            int count;
            while ((count = reader.Read(buffer, 0, buffer.Length)) != 0) {
                await ms.WriteAsync(buffer, 0, count);
            }
            return ms.ToArray();
        }
    }
}

回答by Tarek.Mh

You can use the following method to download an image from a web site and save it, using the Image class:

您可以使用以下方法从网站下载图像并使用 Image 类保存它：

WebRequest req = WebRequest.Create(imageUrl);
WebResponse resp = req.GetResponse();
Image img = Image.FromStream(resp.GetResponseStream());
img.Save(filePath +  fileName + ".jpg");