如何将html代码转换为Xml并生成Dom树

using (SgmlReader reader = new SgmlReader())
        {
            reader.DocType = "HTML";
            reader.InputStream = new StringReader(“html代码”);
            using (StringWriter stringWriter = new StringWriter())
            {
                using (XmlTextWriter writer = new XmlTextWriter(stringWriter))
                {
                    reader.WhitespaceHandling = WhitespaceHandling.None;
                    writer.Formatting = Formatting.Indented;
                    XmlDocument Doc = new XmlDocument();
                    Doc.Load(reader);
                    XmlNodeList XnlInput = Doc.getElementsByTagName_r("input");

                 }

            }

            }

如果是html文件的话

运用.NET Framework类来解析HTML文件、读取数据并不是最容易的。虽然你可以用.NET Framework中的许多类（如StreamReader）来逐行解析文件，但XmlReader提供的API并不是“取出即可用（out of the box）”的，因为HTML的格式不规范。你可以用正则表达式（regular expression），但如果你对这些表达式运用不熟练，你可能开始时会觉得它们有些难。

Microsoft的XML大师Chris Lovett最近在http://www.gotdotnet.com网站上发布了一个新的SGML解析器，叫做SgmlReader，它可以解析HTML文件，甚至将它们转换成一个格式规范的结构。SgmlReader派生于XmlReader，这就是说，你可以像运用诸如XmlTextReader这样的类来解析XML文件那样来解析HTML文件。在本文中，我将介绍如何用SgmlReader类来解析HTML文件并生成格式规范的HTML，从而使你可以用XPath语句来读取数据。

创建一个SgmlReader实例来解析HTML

在开始运用SgmlReader前，从gotdotnet.com下载它，并将assembly放到你的应用程序bin folder中。在可以运用assembly集后，编写代码来读取你想解析的HTML。在本文的例子中，我们用了HttpWebRequest和HttpWebResponse对象来访问一个远程的HTML文件：

 

HttpWebRequest req = (HttpWebRequest)WebRequest.Create(uri);HttpWebResponse res = (HttpWebResponse)req.GetResponse();StreamReader sReader = new StreamReader(res.GetResponseStream());

 

在得到远程的HTML文件后，你就可以创建一个SgmlReader类的实例了。通过将其DocType属性设置为“HTML”，让用户知道你正在处理HTML文件：

 

SgmlReader reader = new SgmlReader();reader.DocType = "HTML";

 

HTML文件的响应流可以被加载到SgmlReader实例，通过其InputStream属性进行解析。首先将HTML文件流加载到一个TextReader对象，然后将TextReader赋值给InputStream属性：

 

reader.InputStream = new StringReader(sReader.ReadToEnd());

 

现在，你就可以通过调用SgmlReader的Read()方法来解析HTML文件了：

 

sw = new StringWriter();writer = new XmlTextWriter(sw);writer.Formatting = Formatting.Indented;while (reader.Read()) { if (reader.NodeType != XmlNodeType.Whitespace) { writer.WriteNode(reader, true); }}

 

因为SgmlReader创建了格式规范的HTML，所以你可以用XPath语句来读取不同的节点。下面的代码说明了如何将SgmlReader生成的输出结果加载到一个XPathNavigator，然后如何用一个XPath语句来查询HTML文件结构：

 

StringBuilder sb = new StringBuilder();XPathDocument doc = new XPathDocument(new StringReader(sw.ToString()));XPathNavigator nav = doc.CreateNavigator();XPathNodeIterator nodes = nav.Select(xpath);while (nodes.MoveNext()) { sb.Append(nodes.Current.Value);}return sb.ToString();

 

点击此处来查看SgmlReader类的一个实例演示。

如果你对XPath语言已经很熟悉，并了解.NET Framework中不同的XML解析API了，那么你就可以很容易地用SgmlReader类来解析HTML并读取数据了。

部分代码C#

            private string GetWellFormedHTML(string uri,string xpath) ...{

            StreamReader sReader = null;

            StringWriter sw = null;

            

SgmlReader reader = null;

 

            XmlTextWriter writer = null;

            try ...{

                if (uri == String.Empty) uri = "http://www.XMLforASP.NET";

                HttpWebRequest req = (HttpWebRequest)WebRequest.Create(uri);

                HttpWebResponse res = (HttpWebResponse)req.GetResponse();

                sReader = new StreamReader(res.GetResponseStream());

                reader = new SgmlReader();

                reader.DocType = "HTML";

                reader.InputStream = new StringReader(sReader.ReadToEnd());

                sw = new StringWriter();

                writer = new XmlTextWriter(sw);

                writer.Formatting = Formatting.Indented;

                //writer.WriteStartElement("Test");

                while (reader.Read()) ...{

                    if (reader.NodeType != XmlNodeType.Whitespace) ...{

                        writer.WriteNode(reader, true);

                    }

                }

                //writer.WriteEndElement();

                if (xpath == null) ...{

                    return sw.ToString();  

                } else ...{ //Filter out nodes from HTML

                    StringBuilder sb = new StringBuilder();

                    XPathDocument doc = new XPathDocument(new StringReader(sw.ToString()));

                    XPathNavigator nav = doc.CreateNavigator();

                    XPathNodeIterator nodes = nav.Select(xpath);

                    while (nodes.MoveNext()) ...{

                        sb.Append(nodes.Current.Value + " ");

                    }

                    return sb.ToString();

                }

            } catch (Exception exp) ...{

                writer.Close();

                reader.Close();

                sw.Close();

                sReader.Close();

                return exp.Message;

            }

        }