URL处理

        /**//// <summary>
        /// Add a query to an URL.
        /// if the URL has not any query,then append the query key and value to it.
        /// if the URL has some queries, then check it if exists the query key already,replace the value, or append the key and value
        /// if the URL has any fragment, append fragments to the URL end.
        /// </summary>
        public static string SafeAddQueryToURL(string key,string value,string url)
        {
            int fragPos = url.LastIndexOf("#");
            string fragment = string.Empty;
            if(fragPos > -1)
            {
                fragment = url.Substring(fragPos);
                url = url.Substring(0,fragPos);
            }
            int querystart = url.IndexOf("?");
            if(querystart < 0)
            {
                url +="?"+key+"="+value;
            }
            else
            {
                Regex reg = new Regex(@"(?<=[&\?])"+key+@"=[^\s&#]*",RegexOptions.Compiled);
                if(reg.IsMatch(url))
                    url = reg.Replace(url,key+"="+value);
                else
                    url += "&"+key+"="+value;
            }
            return url+fragment;
        }
        /**//// <summary>
        /// Remove a query from url
        /// </summary>
        /// <param name="key"></param>
        /// <param name="url"></param>
        /// <returns></returns>
        public static string SafeRemoveQueryFromURL(string key,string url)
        {
            Regex reg = new Regex(@"[&\?]"+key+@"=[^\s&#]*&?",RegexOptions.Compiled);
            return reg.Replace(url,new MatchEvaluator(PutAwayGarbageFromURL));
        }
        private static string PutAwayGarbageFromURL(Match match)
        {
            string value = match.Value;
            if(value.EndsWith("&"))
                return value.Substring(0,1);
            else
                return string.Empty;
        }