在 .NET 中从 URL 读取字符串的最简单方法

Question

给定字符串中的 URL：

http://www.example.com/test.xml

将文件内容从服务器（由 url 指向）下载到 C# 中的字符串中的最简单/最简洁的方法是什么？

我目前的做法是：

WebRequest request = WebRequest.Create("http://www.example.com/test.xml");
WebResponse response = request.GetResponse();
Stream dataStream = response.GetResponseStream();
StreamReader reader = new StreamReader(dataStream);
string responseFromServer = reader.ReadToEnd();

这是很多代码，本质上可能是一行：

string responseFromServer = ????.GetStringFromUrl("http://www.example.com/test.xml");

注意：我不担心异步调用 - 这不是生产代码。

Answer 1

重要提示：这在编写时是正确的，但在 $current_year$ 中，请参阅下面的 HttpClient 答案

---

using(WebClient client = new WebClient()) {
   string s = client.DownloadString(url);
}

Answer 2

上面答案中的方法现已弃用，当前建议使用 HttpClient：

using (HttpClient client = new HttpClient())
{
    string s = await client.GetStringAsync(url);
}

Answer 3

鉴于，在撰写本文时，HttpClient 是执行此功能的唯一剩余的、有效 .Net 机制，并且在任何情况下如果您“不担心异步调用”（这对于 HttpClient 来说似乎是不可避免的），我认为这个函数应该可以满足您的需求：

public static class Http
{
    ///<remarks>NOTE: The <i>HttpCLient</i> class is <b>intended</b> to only ever be instantiated once in any application.</remarks>
    private static readonly HttpClient _client = new();

    /// <summary>Used to retrieve webserver data via simple <b>GET</b> requests.</summary>
    /// <param name="url">A string containing the complete web <b>URL</b> to submit.</param>
    /// <returns>Whatever <i>HttpClient</i> returns after attempting the supplied query (as a <i>Task<string></i> value).</returns>
    /// <exception cref="InvalidOperationException">Returned if the supplied <i>url</i> string is null, empty or whitespace.</exception>
    private static async Task<string> HttpClientKludge( string url )
    {
        if ( string.IsNullOrWhiteSpace( url ) )
            throw new InvalidOperationException( "You must supply a url to interrogate for this function to work." );

        Uri uri;
        try { uri = new Uri( url ); }
        catch ( UriFormatException e ) { return $"{e.Message}\r\n{url}"; }

        return await _client.GetStringAsync( uri );
    }

    /// <summary>Attempts to interrogate a website via the supplied URL and stores the result in a <i>string</i>.</summary>
    /// <param name="url">A string containing a fully-formed, proper URL to retrieve.</param>
    /// <param name="captureExceptions">If <b>TRUE</b>, any Exceptions generated by the operation will be suppressed with their Message returned as the result string, otherwise they're thrown normally.</param>
    /// <returns>The result generated by submitting the request, as a <i>string</i>.</returns>
    public static string Get( string url, bool captureExceptions = true )
    {
        string result;
        try { result = HttpClientKludge( url ).Result; }
        catch (AggregateException e)
        {
            if (!captureExceptions) throw;
            result = e.InnerException is null ? e.Message : e.InnerException.Message;
        }
        return result;
    }
}

完成此操作后，任何时候您想通过简单的 URL+GET 查询来访问网站，您都可以简单地执行以下操作：

string query = "/search?q=Easiest+way+to+read+from+a+URL+into+a+string+in+.NET",
siteResponse = Http.Get( $"https://www.google.com{query}" );
// Now use 'siteResponse' in any way you want...