使用 C# 从 API 下载 PDF 文件

Question

我正在创建一个控制台应用程序，

1. 连接到供应商 API 以提取两个日期之间提交费用的凭证编号，并且
2. 下载随费用提交的收据的 PDF 副本

第一部分，我工作得很好。我可以使用以下代码连接到供应商 API 并解析返回的 XML 以创建凭证编号数组（需要获取 PDF 图像）：

static async Task RunAsyncCR()
        {
            using (var client = new HttpClient())
            {
                var values = new Dictionary<string, string>
                {
                    {"un","SomeUser"},
                    {"pw","SomePassword"},
                    {"method","getVoucherInvoices"},
                    {"fromDate","05/30/2016"},
                    {"toDate", "06/13/2016"}
                };

                var content = new FormUrlEncodedContent(values);

                Console.WriteLine("Connecting...");

                var response = await client.PostAsync("https://www.chromeriver.com/receipts/doit", content);

                Console.WriteLine("Connected...");

                var responseString = await response.Content.ReadAsStringAsync();

                char[] DelimiterChars = {'<'};

                String[] xmlReturn = responseString.Split(DelimiterChars);

                string[] VoucherNumber = new string[500];

                int i = 0;

                foreach (string s in xmlReturn)
                {
                    if (s.Contains("voucherInvoice>") && s != "/voucherInvoice>\n    ")
                    {
                        VoucherNumber[i] = s.Substring(15, 16);

                        i++;
                    }
                }

                Array.Resize(ref VoucherNumber, i);

是的，可能有更好的方法来做到这一点，但它可以工作并返回我期望的值。

现在，我遇到的问题是，当我连接回 API 以检索文件时，我似乎无法将文件下载到指定的文件路径。

我可以使用

连接回 API

            i = 0;

            foreach (string x in VoucherNumber)
            {
                Console.WriteLine("Get receipt: " + x);

                var NewValues = new Dictionary<string, string>
                {
                    {"un","SomeUser"},
                    {"pw","SomePassword"},
                    {"method","getReceiptsWithCoverPage"},
                    {"voucherInvoiceForPdf", VoucherNumber[i]}
                };

                var NewContent = new FormUrlEncodedContent(NewValues);

                var NewResponse = await client.PostAsync("https://www.chromeriver.com/receipts/doit", NewContent);

                string NewResponseString = await NewResponse.Content.ReadAsStringAsync();

但我似乎无法将响应写入有效文件 (PDF)

这是我逐步执行代码时的 Autos 窗口的屏幕截图，我需要在其中下载文件：

我的问题是，从现在开始，我该如何将文件保存到我的系统中？

我尝试获取从执行Console.WriteLine(NewResponseString); 得到的编码响应，并使用System.IO.File.WriteAllLines() 方法，使用指定的文件路径/名称将其写入文件，但这会导致一个空白文件。我也花了一些时间研究 Google/Stackoverflow 的深度，但不明白如何实现我找到的结果。

我们将不胜感激。

Answer 1

所以我认为您需要有关 Streams 的帮助。返回的HttpContent 实际上是一个System.Net.Http.StreamContent 实例，它表明您正在获取内容。它只是从该实例获取流（内容）并将其保存到文件的问题。

var NewResponse = await client.PostAsync("https://www.chromeriver.com/receipts/doit", NewContent);

System.Net.Http.HttpContent content = NewResponse.Content; // actually a System.Net.Http.StreamContent instance but you do not need to cast as the actual type does not matter in this case

using(var file = System.IO.File.Create("somePathHere.pdf")){ // create a new file to write to
    var contentStream = await content.ReadAsStreamAsync(); // get the actual content stream
    await contentStream.CopyToAsync(file); // copy that stream to the file stream
}

---

我恭敬地建议您阅读一下 Streams 的工作原理。这是许多语言中的常见结构，您可能在不久的将来必须再次处理。

Answer 2

首先，您确定有一个文件开头吗？我可以建议使用开源库 PdfSharp。我个人自己使用它，效果很好。至于下载文件，也许这可以帮助你......

同步下载

using System.Net;
WebClient webClient = new WebClient();
webClient.DownloadFile("http://example.com/myfile.txt", @"c:\\myfile.txt");

http://www.csharp-examples.net/download-files/

Answer 3

首先从 NewResponse 创建 StreamReader

Stream receiveStream = NewResponse.GetResponseStream ();
StreamReader readStream = new StreamReader (receiveStream, Encoding.UTF8);

然后定义一个 StremaWriter 写入文件。

using (var writer = new StreamWriter(@"C:\MyNewFile.pdf", append: false))
{
    writer.Write(readStream.ReadToEnd());
}

替代方法是

var httpContent = NewResponse.Content; 

using(var newFile = System.IO.File.Create(@"C:\MyNewFile.pdf"))
{ 
    var stream = await httpContent.ReadAsStreamAsync();
    await stream.CopyToAsync(newFile);
}

Answer 4

这是我所做的，没有找到任何其他满足我情况的解决方案：

using (var client = new System.Net.Http.HttpClient())

{
  client.DefaultRequestHeaders.Add("Authorization", "someapikey");
  client.BaseAddress = new Uri("https://someurl.com");
  byte[] bytes = client.GetByteArrayAsync(client.BaseAddress).ConfigureAwait(false).GetAwaiter().GetResult();

  
  string pdfFilePath = @"c:\somepath"
  System.IO.File.WriteAllBytes(pdfFilePath, bytes);

  //Note that below is only to open PDF in standard viewer, not necessary
  var process = new System.Diagnostics.Process();
  var startInfo = new System.Diagnostics.ProcessStartInfo()
{
    FileName=pdfFilePath,
    WorkingDirectory = System.IO.Path.GetDirectoryName(pdfFilePath),
    UseShellExecute = true
}

  process.StartInfo = startInfo;
  process.Start();

}

Answer 5

使用此代码从 API 下载 pdf。它将字符串数据转换为字节，并为您提供必要的解决方案。

HttpWebRequest request = (HttpWebRequest) WebRequest.Create(URL);

request.ContentType = "application/pdf;charset=UTF-8";
request.Method = "GET";

using(HttpWebResponse response = (HttpWebResponse) request.GetResponse()) {

    BinaryReader bin = new BinaryReader(response.GetResponseStream());

    byte[] buffer = bin.ReadBytes((Int32) response.ContentLength);

    Response.Buffer = true;
    Response.Charset = "";

    Response.AppendHeader("Content-Disposition", "attachment; filename=+ filename); 

    Response.Cache.SetCacheability(HttpCacheability.NoCache);

    Response.ContentType = "application/pdf";

    Response.BinaryWrite(buffer);

    Response.Flush();

    Response.End();
}