一 XPath的概念

1 XPath是对XML进行查询的表达式

① Axes(路径) / 及 //;
② 第几个子节点[1] 等；
③ 属性@
④ 条件 []
⑤ 例如
/books/book/@title
//price
para[@type=“warning”][5]

2 使用XPath

① XmlDocument doc=new XmlDocument();
② doc.LoadXml(strXml);
③ XmlElement root=doc.DocumentElement;
④ XmlNodeList nodes=
root.SelectNodes(strXPath);
XmlNode node=root.SelectSingleNode(strXPath);
node的.NodeType .InnerXml及.Value;

3 使用Xlst进行转换

XMLDocument doc=new XMLDocument();
doc.Load(@".\BookList.xml");
XPathNavigator nav=doc.Createnavigator();
nav.MoveToRoot();
XslTransform xt=new XslTransform();
xt.Load(@".\BookList.xslt");
XmlTextWriter writer=new XmlTextWriter(Console.Out);
xt.Transform(nav,null,writer);

using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;namespace 网络爬虫
{public class Crawler{private WebClient webClient = new WebClient();private Hashtable urls = new Hashtable();private int count = 0;static void Main(string[] args){Crawler myCrawler = new Crawler();string startUrl = "http://www.cnblogs.com/dstang2000";if (args.Length >= 1)startUrl = args[0];myCrawler.urls.Add(startUrl, false);//加入初始页面new Thread(new ThreadStart(myCrawler.Crawl)).Start();//开始爬行Console.ReadKey();}private void Crawl(){Console.WriteLine("开始爬行了.....");while(true){string current = null;foreach(string url in urls.Keys)//找到一个还没有下载过的链接{if ((bool)urls[url])continue;//已经下载过的，不再下载current = url;}if (current == null || count > 10)break;Console.WriteLine("爬行" + current + "页面！");string html = DownLoad(current);//下载urls[current] = true;count++;Parse(html);//解析，并加入新的链接}Console.WriteLine("爬行结束");}public string DownLoad(string url){try{HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);req.Timeout = 30000;HttpWebResponse response = (HttpWebResponse)req.GetResponse();byte[] buffer = ReadInstreamIntoMemory(response.GetResponseStream());string fileName = count.ToString();FileStream fs = new FileStream(fileName, FileMode.OpenOrCreate);fs.Write(buffer, 0, buffer.Length);fs.Close();string html = Encoding.UTF8.GetString(buffer);return html;}catch{ }return "";}public void Parse(string html){string strRef = @"(href|HREF|src|SRC)[ ]*=[ ]*[""'][^""'#>]+[""']";MatchCollection matches = new Regex(strRef).Matches(html);foreach(Match match in matches){strRef = match.Value.Substring(match.Value.IndexOf('=') + 1).Trim('"', '\'', '#', ' ', '>');if (strRef.Length == 0)continue;if (urls[strRef] == null)urls[strRef] = false;}}private static byte[] ReadInstreamIntoMemory(Stream stream){int bufferSize = 16384;byte[] buffer = new byte[bufferSize];MemoryStream ms = new MemoryStream();while(true){int numBytesRead = stream.Read(buffer, 0, bufferSize);if (numBytesRead <= 0)break;ms.Write(buffer, 0, numBytesRead);}return ms.ToArray();}}
}