由于工作需要写了一个包括所有Url的正则表达式，用来验证返回的Url是否符合RFC1738规定。
有兴趣的同学可以去看RFC1378关于Url部分的介绍（http://www.ietf.org/rfc/rfc1738.txt），本文中的代码是按其规定编写的。
在没有了解RFC1738的时候，一直以为Url的正则表达式很简单，没想到Url有这么多分类，更没想到一个普通的http的正则表达式也不是那么简单。
以下是我搜到的关于http的正则表达式：
http://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]*)?
当然这已经满足大部分人的需求了，但是如果需要严格的验证的话还是要符合RFC1738了。
Url包括Http，Ftp,News,Nntpurl,Telnet,Gopher,Wais,Mailto,File,Prosperurl和Otherurl。
呵呵，废话不多说了，上代码
#region Http
string lowalpha = @"[a-z]";
string hialpha = @"[A-Z]";
string alpha = String.Format(@"({0}|{1})", lowalpha, hialpha);
string digit = @"[0-9]";
string safe = @"(\$|-|_|\.|\+)";
string extra = @"(!|\*|'|\(|\)|,)";
string hex = String.Format(@"({0}|A|B|C|D|E|F|a|b|c|d|e|f)", digit);
string escape = String.Format(@"(%{0}{0})", hex);
string unreserved = String.Format(@"({0}|{1}|{2}|{3})", alpha, digit, safe, extra);
string uchar = String.Format(@"({0}|{1})", unreserved, escape);
string reserved = @"(;|/|\?|:|@|&|=)";
string xchar = String.Format(@"({0}|{1}|{2})", unreserved, reserved, escape);
string digits = String.Format(@"({0}+)", digit);
string alphadigit = String.Format(@"({0}|{1})", alpha, digit);
string domainlabel = String.Format(@"({0}|{0}({0}|-)*{0})", alphadigit);
string toplabel = String.Format(@"({0}|{0}({1}|-)*{1})", alpha, alphadigit);
string hostname = String.Format(@"(({0}\.)*{1})", domainlabel, toplabel);
string hostnumber = String.Format(@"{0}\.{0}\.{0}\.{0}", digits);
string host = String.Format(@"({0}|{1})", hostname, hostnumber);
string port = digits;
string hostport = String.Format(@"({0}(:{1}){{0,1}})", host, port);
string hsegment = String.Format(@"(({0}|;|:|@|&|=)*)", uchar);
string search = String.Format(@"(({0}|;|:|@|&|=)*)", uchar);
string hpath = String.Format(@"{0}(/{0})*", hsegment);
string httpurl = String.Format(@"http://{0}(/{1}(\?{2}){{0,1}}){{0,1}}", hostport, hpath, search);
#endregion
#region Ftp
string user = String.Format(@"(({0}|;|\?|&|=)*)", uchar);
string password = String.Format(@"(({0}|;|\?|&|=)*)", uchar);
string login = String.Format(@"(({0}(:{1}){{0,1}}@){{0,1}}{2})", user, password, hostport);
string fsegment = String.Format(@"(({0}|\?|:|@|&|=)*)", uchar);
string ftptype = @"(A|I|D|a|i|d)";
string fpath = String.Format(@"({0}(/{0})*)", fsegment);
string ftpurl = String.Format(@"ftp://{0}(/{1}(;type={2}){{0,1}}){{0,1}}", login, fpath, ftptype);
#endregion
#region News
string group = String.Format(@"({0}({0}|{1}|-|\.|\+|_)*)", alpha, digit);
string article = String.Format(@"(({0}|;|/|\?|:|&|=)+@{1})", uchar, host);
string grouppart = String.Format(@"(\*|{0}|{1})", group, article);
string newsurl = String.Format(@"(news:{0})", grouppart);
#endregion
#region Nntpurl
string nntpurl = String.Format(@"nntp://{0}/{1}(/{2}){{0,1}}", hostport, group, digits);
#endregion
#region Telnet
string telneturl = String.Format(@"telnet://{0}/{{0,1}}", login);
#endregion
#region Gopher
string gtype = xchar;
string selector = String.Format(@"({0}*)", xchar);
string gopherplus_string = String.Format(@"({0}*)", xchar);
string gopherurl = String.Format(@"gopher://{0}(/({1}({2}(%09{3}(%09{4}){{0,1}}){{0,1}}){{0,1}}){{0,1}}){{0,1}}", hostport, gtype, selector, search, gopherplus_string);
#endregion
复制代码
#region Wais
string database = String.Format(@"({0}*)", uchar);
string wtype = String.Format(@"({0}*)", uchar);
string wpath = String.Format(@"({0}*)", uchar);
string waisdatabase = String.Format(@"(wais://{0}/{1})", hostport, database);
string waisindex = String.Format(@"(wais://{0}/{1}\?{2})", hostport, database, search);
string waisdoc = String.Format(@"(wais://{0}/{1}/{2}/{3})", hostport, database, wtype, wpath);
string waisurl = String.Format(@"{0}|{1}|{2}", waisdatabase, waisindex, waisdoc);
#endregion
#region Mailto
string encoded822addr = String.Format(@"({0}+)", xchar);
string mailtourl = String.Format(@"mailto:{0}", encoded822addr);
#endregion
#region File
string fileurl = String.Format(@"file://({0}{{0,1}}|localhost)/{1}", host, fpath);
#endregion
#region Prosperourl
string fieldname = String.Format(@"({0}|\?|:|@|&)", uchar);
string fieldvalue = String.Format(@"({0}|\?|:|@|&)", uchar);
string fieldspec = String.Format(@"(;{0}={1})", fieldname, fieldvalue);
string psegment = String.Format(@"(({0}|\?|:|@|&|=)*)", uchar);
string ppath = String.Format(@"({0}(/{0})*)", psegment);
string prosperourl = String.Format(@"prospero://{0}/{1}({2})*", hostport, ppath, fieldspec);
#endregion
#region Otherurl
//otherurl equal genericurl
string urlpath = String.Format(@"(({0})*)", xchar);
string scheme = String.Format(@"(({0}|{1}|\+|-|\.)+)", lowalpha, digit);
string ip_schemepar = String.Format(@"(//{0}(/{1}){{0,1}})", login, urlpath);
string schemepart = String.Format(@"(({0})*|{1})", xchar, ip_schemepar);
string genericurl = String.Format(@"{0}:{1}", scheme, schemepart);
string otherurl = genericurl;
#endregion
有了Pattern剩下的就简单多了，无非就是正则表达式的验证了，以Http为例：
Http的pattern为string httpurl,假设要验证的Url为url，所以验证url的代码如下：
Regex regex = new Regex(httpurl);
bool isMatchHttp = regex.IsMatch(url);