asp.net如何过滤html标签,但是要留下<a>标签

Question

<div class="mod" id="yhp-focus"><a href="http://news.cn.yahoo.com/" target="_blank" class="headlink" name="yhp0806/focus/title">今日焦点</a>
<em class="fixfloat"><a name="yhp0806/focus/my" target="_blank" href=http://www.e-businessmen.org/>2009网商评选30强闪耀登场！</a>女友生日选浪漫餐厅，上关系点评</a></em><a href=http://news.cn.yahoo.com/newspic/news_newspic_article.html?id=318 target="_blank" class="imgblock" name="yhp0806/focus/img1"><img src="http://cn.yimg.com/sp/news/img/zsc09072432.jpg" alt="92岁美籍老人获“中国绿卡”" width="160" height="120" />92岁美籍老人获“中国绿卡”</a>
<h2><a href=http://news.cn.yahoo.com/09-07-/1063/2jlaj.html target="_blank" name="yhp0806/focus/news1">我国拟规定上下班途中受机动车伤害不算工伤</a>  <a href= target="_blank" name="yhp0806/focus/news1"></a></h2><li><a href=http://finance.cn.yahoo.com/ target="_blank" class="cate" name="yhp0806/focus/cate1">[财经]</a>  <a href=http://finance.cn.yahoo.com/ class=hot target="_blank" name="yhp0806/focus/news2">央行：继续实施适度宽松货币政策</a>  <a href=http://biz.cn.yahoo.com/stock.html target="_blank" name="yhp0806/focus/news3">光大证券获IPO批文</a></li><li><a href=http://autos.cn.yahoo.com/ target="_blank" class="cate" name="yhp0806/focus/cate2">[汽车]</a>  <a href=http://autos.yahoo.com.cn target="_blank" name="yhp0806/focus/news4">六款上半年上市小型车全攻略</a>  <a href=http://yxk.cn.yahoo.com/articles/20090725/hmq.html target="_blank" name="yhp0806/focus/news5"> 醉驾肇事者撞死4人获死刑</a></li><li><a href=http://lady.cn.yahoo.com/index.html target="_blank" class="cate" name="yhp0806/focus/cate3">[女性] 分手后不该问的事</a>  <a href=http://bbs.cn.yahoo.com/lady/forumview.php?bn=%C2%E9%C0%B1%C6%C5%CF%B1 target="_blank" name="yhp0806/focus/news6">一个凤凰男的自白</a>  <a href=http://lady.cn.yahoo.com/pic/index.html target="_blank" name="yhp0806/focus/news7">女人抢手的标准</a></li><li><a href=http://ent.cn.yahoo.com/ target="_blank" class="cate" name="yhp0806/focus/cate4">[娱乐]</a>  <a href=http://ent.cn.yahoo.com/ target="_blank" name="yhp0806/focus/news8">曝孙楠不想离婚 潘蔚以死相逼</a>  <a href=http://yxk.cn.yahoo.com/articles/20090725/hmf.html target="_blank" name="yhp0806/focus/news9">袁泉穿短裙难掩春光外泄</li><li><a href=http://news.cn.yahoo.com/ target="_blank" class="cate" name="yhp0806/focus/cate5">[资讯]</a>  <a href=http://news.cn.yahoo.com/newspic/news_newspic_article.html?id=315 target="_blank" name="yhp0806/focus/news10">沈阳8000美女角逐亚运空姐</a>  <a href=http://news.cn.yahoo.com/newspic/news_newspic_article.html?id=314 target="_blank" name="yhp0806/focus/news11">武汉最美女交警酷暑中执勤</a></li><em><a name="yhp0806/my/ad" target="_blank" href=http://guanxi.koubei.com/pro.php?f=1_P16_20081002 class=hot>最怕洗碗在哪有卖洗碗机？上关系求助，生活信息连连看</a></em> 关系<ul class="pt-list"><img src="http://cn.yimg.com/sp/sportsimages/dj/09072405.jpg" alt="" /></a>日常警惕最伤肾的四大生活方式</a><br>-男人吃海鲜喝啤酒伤肾？<img src="http://cn.yimg.com/sp/sportsimages/dj/09072404.jpg" alt="" /></a>国产红旗SUV，买这车老霸道了</a><br>-SUV国产车推荐，支持国货</ul>
<ul class="txt-list dotlist">
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</ul><div class="yhp-txtpush fixfloat">
推广</span>
<span id="ad-area-bj-t123" style="float:right">
<script>
//loadAsyncData('http://cn.yahoo.com/haoyue_area.php?page=homepage&position=t123','ad-area-bj-t123');
</script>
<iframe src="http://api.ads.vip.cnh.yahoo.com/ads_area/ads_area.php?page=homepage&position=t123" style="width:532px;height:24px;border:none;" scrolling="no" frameborder=0></iframe>
</span></div></b>
</b>
</b>
</b>
</div><div class="admod fixfloat">
</div><span id="ad-area-bj-desk">
<script>
//loadAsyncData('http://cn.yahoo.com/haoyue_area.php?page=homepage&position=desk1234','ad-area-bj-desk');
</script>
<iframe src="http://api.ads.vip.cnh.yahoo.com/ads_area/ads_area.php?page=homepage&position=desk1234" style="width:160px;height:90px;border:none;" scrolling="no" frameborder=0></iframe>
</span>
</div> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" >
<head><title>
无标题页
</title></head>
<body>
    
</body>
</html>
这么一串代码,除了<a>标签,其他要全部过滤掉,怎么实现啊，  请高手写个代码吧

Answer 1

   string str = @"<div class=""mod"" id=""yhp-focus""> <a href=""http://news.cn.yahoo.com/"" target=""_blank"" class=""headlink"" name=""yhp0806/focus/title"">今日焦点</a> 
<em class=""fixfloat""> <a name=""yhp0806/focus/my"" target=""_blank"" href=http://www.e-businessmen.org/>2009网商评选强闪耀登场！</a>女友生日选浪漫餐厅，上关系点评</a> </em> <a href=http://news.cn.yahoo.com/newspic/news_newspic_article.html?id=318 target=""_blank"" class=""imgblock"" name=""yhp0806/focus/img1""> <img src=""http://cn.yimg.com/sp/news/img/zsc09072432.jpg"" alt=""92岁美籍老人获“中国绿卡”"" width=""160"" height=""120"" />92岁美籍老人获“中国绿卡”</a> 
<h2> <a href=http://news.cn.yahoo.com/09-07-/1063/2jlaj.html target=""_blank"" name=""yhp0806/focus/news1"">我国拟规定上下班途中受机动车伤害不算工伤</a>  <a href= target=""_blank"" name=""yhp0806/focus/news1""> </a> </h2> <li> <a href=http://finance.cn.yahoo.com/ target=""_blank"" class=""cate"" name=""yhp0806/focus/cate1"">[财经] </a>  <a href=http://finance.cn.yahoo.com/ class=hot target=""_blank"" name=""yhp0806/focus/news2"">央行：继续实施适度宽松货币政策</a>  <a href=http://biz.cn.yahoo.com/stock.html target=""_blank"" name=""yhp0806/focus/news3"">光大证券获IPO批文</a> </li> <li> <a href=http://autos.cn.yahoo.com/ target=""_blank"" class=""cate"" name=""yhp0806/focus/cate2"">[汽车] </a>  <a href=http://autos.yahoo.com.cn target=""_blank"" name=""yhp0806/focus/news4"">六款上半年上市小型车全攻略</a>  <a href=http://yxk.cn.yahoo.com/articles/20090725/hmq.html target=""_blank"" name=""yhp0806/focus/news5""> 醉驾肇事者撞死人获死刑</a> </li> <li> <a href=http://lady.cn.yahoo.com/index.html target=""_blank"" class=""cate"" name=""yhp0806/focus/cate3"">[女性] 分手后不该问的事</a>  <a href=http://bbs.cn.yahoo.com/lady/forumview.php?bn=%C2%E9%C0%B1%C6%C5%CF%B1 target=""_blank"" name=""yhp0806/focus/news6"">一个凤凰男的自白</a>  <a href=http://lady.cn.yahoo.com/pic/index.html target=""_blank"" name=""yhp0806/focus/news7"">女人抢手的标准</a> </li> <li> <a href=http://ent.cn.yahoo.com/ target=""_blank"" class=""cate"" name=""yhp0806/focus/cate4"">[娱乐] </a>  <a href=http://ent.cn.yahoo.com/ target=""_blank"" name=""yhp0806/focus/news8"">曝孙楠不想离婚潘蔚以死相逼</a>  <a href=http://yxk.cn.yahoo.com/articles/20090725/hmf.html target=""_blank"" name=""yhp0806/focus/news9"">袁泉穿短裙难掩春光外泄</li> <li> <a href=http://news.cn.yahoo.com/ target=""_blank"" class=""cate"" name=""yhp0806/focus/cate5"">[资讯] </a>  <a href=http://news.cn.yahoo.com/newspic/news_newspic_article.html?id=315 target=""_blank"" name=""yhp0806/focus/news10"">沈阳美女角逐亚运空姐</a>  <a href=http://news.cn.yahoo.com/newspic/news_newspic_article.html?id=314 target=""_blank"" name=""yhp0806/focus/news11"">武汉最美女交警酷暑中执勤</a> </li> <em> <a name=""yhp0806/my/ad"" target=""_blank"" href=http://guanxi.koubei.com/pro.php?f=1_P16_20081002 class=hot>最怕洗碗在哪有卖洗碗机？上关系求助，生活信息连连看</a> </em> 关系<ul class=""pt-list""> <img src=""http://cn.yimg.com/sp/sportsimages/dj/09072405.jpg"" alt="""" /> </a>日常警惕最伤肾的四大生活方式</a> <br>-男人吃海鲜喝啤酒伤肾？<img src=""http://cn.yimg.com/sp/sportsimages/dj/09072404.jpg"" alt="""" /> </a>国产红旗SUV，买这车老霸道了</a> <br>-SUV国产车推荐，支持国货</ul> 
<ul class=""txt-list dotlist""> 
<a href=http://guanxi.koubei.com/jake/fun/dj090724_4.html?f=R3_hp_fake090205 target=""_blank"" name=""yhp0806/my/link3"">[常识] 哪些植物在室内养对人体有好处</a> <em>(235人答复) </em> </li> 
<a href=http://guanxi.koubei.com/jake/fun/dj090724_1.html?f=R3_hp_fake090205 target=""_blank"" name=""yhp0806/my/link4"">[点评] 上海吴江路老街必吃的四种小吃</a> <em>(394人浏览) </em> </li> 
<a href=http://guanxi.koubei.com/jake/fun/dj090724_5.html?f=R3_hp_fake090205 target=""_blank"" name=""yhp0806/my/link5"">[投票] 给你一百万投资，你会怎样打理</a> <em>(799人参与) </em> </li> 
</ul> <div class=""yhp-txtpush fixfloat""> 
推广</span> 
<span id=""ad-area-bj-t123"" style=""float:right""> 
<script> 
//loadAsyncData('http://cn.yahoo.com/haoyue_area.php?page=homepage&position=t123','ad-area-bj-t123'); 
</script> 
<iframe src=""http://api.ads.vip.cnh.yahoo.com/ads_area/ads_area.php?page=homepage&position=t123"" style=""width:532px;height:24px;border:none;"" scrolling=""no"" frameborder=0> </iframe> 
</span> </div> </b> 
</b> 
</b> 
</b> 
</div> <div class=""admod fixfloat""> 
</div> <span id=""ad-area-bj-desk""> 
<script> 
//loadAsyncData('http://cn.yahoo.com/haoyue_area.php?page=homepage&position=desk1234','ad-area-bj-desk'); 
</script> 
<iframe src=""http://api.ads.vip.cnh.yahoo.com/ads_area/ads_area.php?page=homepage&position=desk1234"" style=""width:160px;height:90px;border:none;"" scrolling=""no"" frameborder=0> </iframe> 
</span> 
</div> <!DOCTYPE html PUBLIC ""-//W3C//DTD XHTML 1.0 Transitional//EN"" ""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd""> <html xmlns=""http://www.w3.org/1999/xhtml"" > 
<head> <title> 
无标题页
</title> </head> 
<body> 
    
</body> 
</html>";            str = System.Text.RegularExpressions.Regex.Replace(str, @"<(?!(a\s+)|(/a>))[^<>]*?>", "", RegexOptions.IgnoreCase);
            Response.Write(Server.HtmlEncode(str));

Answer 2

太棒了，不过问下为啥要用Server.HtmlEncode?

Answer 3

是为了你看方便，
就算有div,你也看来出来。

Answer 4

是为了你看方便， 
否则，，
就算有div,你也看来出来。