网上关于Url转链接（href）的正则表达式一搜一大堆，但真正好用的没几个。

后来在Matthew O'Riordan的Blog上发现一个很好用的正则表达式，是用Javascript写的，代码如下：

(

  ( // brackets covering match for protocol (optional) and domain

    ([A-Za-z]{3,9}:(?:\/\/)?) // match protocol, allow in format http:// or mailto:

    (?:[\-;:&=\+\$,\w]+@)? // allow something@ for email addresses

    [A-Za-z0-9\.\-]+ // anything looking at all like a domain, non-unicode domains

    | // or instead of above

    (?:www\.|[\-;:&=\+\$,\w]+@) // starting with something@ or www.

    [A-Za-z0-9\.\-]+   // anything looking at all like a domain

  )

  ( // brackets covering match for path, query string and anchor

    (?:\/[\+~%\/\.\w\-]*) // allow optional /path

    ?\??(?:[\-\+=&;%@\.\w]*) // allow optional query string starting with ?

    #?(?:[\.\!\/\\\w]*) // allow optional anchor #anchor

  )? // make URL suffix optional

)

针对我们的使用场景（只对http或https开头的Url进行转换）简化了一下，并用C#写出：

public static class ContentFormatter

{

    private static readonly Regex Url_To_Link = new Regex(@"(?<url>

        (https?:(?:\/\/)?)        # match protocol, allow in format http:// or https://

        [A-Za-z0-9\.\-]+          # anything looking at all like a domain, non-unicode domains

        (                         # brackets covering match for path, query string and anchor

        (?:\/[\+~%\/\.\w\-]*)?    # allow optional /path

        \??(?:[\-\+=&;%@\.\w]*?)  # allow optional query string starting with ?

        \#?(?:[\.\!\/\\\w\-]*)      # allow optional anchor #anchor

        )?                        # make URL suffix optional

        )",

        RegexOptions.Compiled | RegexOptions.Multiline | RegexOptions.IgnorePatternWhitespace,

        TimeSpan.FromMilliseconds(100));

    public static string UrlToLink(string text)

    {

        if (string.IsNullOrEmpty(text)) return string.Empty;

        return Url_To_Link.Replace(text, "<a href=\"${url}\" target=\"_blank\">${url}</a>");

    }

}