asp.net下URL处理两个小工具方法

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有的时候我们要操作一个URL地址中查询参数，为了不破坏URL的原有结构，我们一般不能直接在URL的后面加&query=value，特别是我们的URL中有多个参数时，这种处理更麻烦。
下面两个小方法就是专门用来为一个URL添加一个查询参数或删除一个查询参数，这两个方法隐藏了原URL有无参数，是不是原来就有这个参数，有没有fragment(#anchor)这些细节和处理
/**//// <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;
}

测试：
string s = "http://www.cnblogs.com/?a=1&b=2&c=3#tag";
WL(SafeRemoveQueryFromURL("a",s));
WL(SafeRemoveQueryFromURL("b",s));
WL(SafeRemoveQueryFromURL("c",s));
WL(SafeAddQueryToURL("d","new",s));
WL(SafeAddQueryToURL("a","newvalue",s));
// 输出如下:
// http://www.cnblogs.com/?b=2&c=3#tag
// http://www.cnblogs.com/?a=1&c=3#tag
// http://www.cnblogs.com/?a=1&b=2#tag
// http://www.cnblogs.com/?a=1&b=2&c=3&d=new#tag
// http://www.cnblogs.com/?a=newvalue&b=2&c=3#tag

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