如何在C#中用正则表达式从字符串中提取域名？

Question

我想提取顶级域名和国家顶级域名从字符串与正则表达式。我测试了许多如下代码的正则表达式：

var linkParser = new Regex(@"\b(?:https?://|www\.)\S+\b", RegexOptions.Compiled | RegexOptions.IgnoreCase);
Match m = linkParser.Match(Url);
Console.WriteLine(m.Value);

但是这些代码都不能正确地做到这一点。用户输入的文本字符串可以是以下语句：

jonasjohn.com
http://www.jonasjohn.de/snippets/csharp/
jonasjohn.de
www.jonasjohn.de/snippets/csharp/
http://www.answers.com/article/1194427/8-habits-of-extraordinarily-likeable-people
http://www.apple.com
https://www.cnn.com.au
http://www.downloads.news.com.au
https://ftp.android.co.nz
http://global.news.ca
https://www.apple.com/
https://ftp.android.co.nz/
http://global.news.ca/
https://www.apple.com/
https://johnsmith.eu
ftp://johnsmith.eu
johnsmith.gov.ae
johnsmith.eu
www.jonasjohn.de
www.jonasjohn.ac.ir/snippets/csharp
http://www.jonasjohn.de/
ftp://www.jonasjohn.de/
https://subdomain.abc.def.jonasjohn.de/test.htm

我测试的正则表达式：

^(?:https?:\/\/)?(?:[^@\/\n]+@)?(?:www\.)?([^:\/\n]+)"

\b(?:https?://|www\.)\S+\b

://(?<host>([a-z\\d][-a-z\\d]*[a-z\\d]\\.)*[a-z][-a-z\\d]+[a-z])

还有太多，我只需要域名，我不需要一个协议或子域。如: Domainname.gTLD、DomainName.ccTLD或DomainName.xyz.ccTLD

我从PUBLIC SUFFIX上拿到了他们的名单

当然，我在stackoverflow.com上看到了很多帖子，但都没有回应我。

Answer 1

根据Lidqy answer的说法，我编写了这个函数，我认为它支持大多数可能的情况，如果输入值不在这个范围内，您可以将其作为一个例外。

public static string ExtractDomainName(string Url)
        {
            var regex = new Regex(@"^((https?|ftp)://)?(www\.)?(?<domain>[^/]+)(/|$)");

            Match match = regex.Match(Url);

            if (match.Success)
            {
                string domain = match.Groups["domain"].Value;
                int freq = domain.Where(x => (x == '.')).Count();
                while (freq > 2)
                {
                    if (freq > 2)
                    {
                        var domainSplited = domain.Split('.', 2);
                        domain = domainSplited[1];
                        freq = domain.Where(x => (x == '.')).Count();
                    }
                }
                return domain;
            }
            else
            {
                return String.Empty;
            }
        }

Answer 2

您不需要使用正则表达式来解析URL。如果您有一个有效的URL，您可以使用Uri构造函数或Uri.TryCreate来解析它：

if(Uri.TryCreate("http://google.com/asdfs",UriKind.RelativeOrAbsolute,out var uri))
{
    Console.WriteLine(uri.Host);
}

不过，www.jonasjohn.de/snippets/csharp/和jonasjohn.de/snippets/csharp/不是有效的URL。TryCreate仍然可以将它们解析为相对URL，但是读取Host会抛出System.InvalidOperationException: This operation is not supported for a relative URI.

在这种情况下，您可以使用UriBuilder类来解析和修改URL，例如：

var bld=new UriBuilder("jonasjohn.com");
Console.WriteLine(bld.Host);

这是打印

jonasjohn.com

设置Scheme属性会生成一个有效的、完整的URL：

bld.Scheme="https";
Console.WriteLine(bld.Uri);

这会产生以下结果：

https://jonasjohn.com:80/

Answer 3

var rx = new Regex(@"^((https?|ftp)://)?(www\.)?(?<domain>[^/]+)(/|$)");
var data = new[] {           "jonasjohn.com",
                             "http://www.jonasjohn.de/snippets/csharp/",
                             "jonasjohn.de",
                             "www.jonasjohn.de/snippets/csharp/",
                             "http://www.answers.com/article/1194427/8-habits-of-extraordinarily-likeable-people",
                             "http://www.apple.com",
                             "https://www.cnn.com.au",
                             "http://www.downloads.news.com.au",
                             "https://ftp.android.co.nz",
                             "http://global.news.ca",
                             "https://www.apple.com/",
                             "https://ftp.android.co.nz/",
                             "http://global.news.ca/",
                             "https://www.apple.com/",
                             "https://johnsmith.eu",
                             "ftp://johnsmith.eu",
                             "johnsmith.gov.ae",
                             "johnsmith.eu",
                             "www.jonasjohn.de",
                             "www.jonasjohn.ac.ir/snippets/csharp",
                             "http://www.jonasjohn.de/",
                             "ftp://www.jonasjohn.de/",
                             "https://subdomain.abc.def.jonasjohn.de/test.htm"
                         };

        foreach (var dat in data) {
            var match = rx.Match(dat);
            if (match.Success)
                Console.WriteLine("{0} => {1}", dat, match.Groups["domain"].Value);
            else {
                Console.WriteLine("{0} => NO MATCH", dat);
            }
        }