之前做聊天室时，由于在聊天室中提供了新闻阅读的功能，写了一个从网页中抓取信息（如最新的头条新闻，新闻的来源，标题，内容等）的类，本文将介绍如何使用这个类来抓取网页中需要的信息。本文将以抓取博客园首页的博客标题和链接为例：

上图显示的是博客园首页的DOM树，显然只需提取出class为post_item的div，再重中提取出class为titlelnk的a标志即可。这样的功能可以通过以下函数来实现：

/// 
/// 在文本html的文本查找标志名为tagName,并且属性attrName的值为attrValue的所有标志/// 例如：FindTagByAttr(html, "div", "class", "demo")/// 返回所有class为demo的div标志/// 
public static List
     
       FindTagByAttr(String html, String tagName, String attrName, String attrValue){    String format = String.Format(@"<{0}\s[^<>]*{1}\s*=\s*(\x27|\x22){2}(\x27|\x22)[^<>]*>", tagName, attrName, attrValue);    return FindTag(html, tagName, format);}public static List
      
        FindTag(String html, String name, String format){    Regex reg = new Regex(format, RegexOptions.IgnoreCase);    Regex tagReg = new Regex(String.Format(@"<(\/|)({0})(\s[^<>]*|)>", name), RegexOptions.IgnoreCase);    List
       
         tags = new List
        
         ();    int start = 0;    while (true)    {        Match match = reg.Match(html, start);        if (match.Success)        {            start = match.Index + match.Length;            Match tagMatch = null;            int beginTagCount = 1;            while (true)            {                tagMatch = tagReg.Match(html, start);                if (!tagMatch.Success)                {                    tagMatch = null;                    break;                }                start = tagMatch.Index + tagMatch.Length;                if (tagMatch.Groups[1].Value == "/") beginTagCount--;                else beginTagCount++;                if (beginTagCount == 0) break;            }            if (tagMatch != null)            {                HtmlTag tag = new HtmlTag(name, match.Value, html.Substring(match.Index + match.Length, tagMatch.Index - match.Index - match.Length));                tags.Add(tag);            }            else            {                break;            }        }        else        {            break;        }    }    return tags;}
        
       
      
     

有了以上函数，就可以提取需要的HTML标志了，要实现抓取，还需要一个下载网页的函数：

public static String GetHtml(string url){    try    {        HttpWebRequest req = HttpWebRequest.Create(url) as HttpWebRequest;        req.Timeout = 30 * 1000;        HttpWebResponse response = req.GetResponse() as HttpWebResponse;        Stream stream = response.GetResponseStream();        MemoryStream buffer = new MemoryStream();        Byte[] temp = new Byte[4096];        int count = 0;        while ((count = stream.Read(temp, 0, 4096)) > 0)        {            buffer.Write(temp, 0, count);        }        return Encoding.GetEncoding(response.CharacterSet).GetString(buffer.GetBuffer());    }    catch    {        return String.Empty;    }}

以下以抓取博客园首页的文章标题和链接为例，介绍如何使用HtmlTag类来抓取网页信息：

class Program{    static void Main(string[] args)    {        String html = HtmlTag.GetHtml("http://www.cnblogs.com");        List
     
       tags = HtmlTag.FindTagByAttr(html, "div", "id", "post_list");        if (tags.Count > 0)        {            List
      
        item_tags = tags[0].FindTagByAttr("div", "class", "post_item");            foreach (HtmlTag item_tag in item_tags)            {                List
       
         a_tags = item_tag.FindTagByAttr("a", "class", "titlelnk");                if (a_tags.Count > 0)                {                    Console.WriteLine("标题:{0}", a_tags[0].InnerHTML);                    Console.WriteLine("链接:{0}", a_tags[0].GetAttribute("href"));                    Console.WriteLine("");                }            }        }    }}
       
      
     

运行结果如下：

来源：http://www.cnblogs.com/lucc/archive/2010/05/18/1738718.html