玩轉C#之【爬蟲】

介紹

基礎概念

爬蟲可以做哪些事情?

爬蟲的攻防

下載html(HttpWebRequest)

string html = string.Empty;

HttpWebRequest request = HttpWebRequest.Create(url) as HttpWebRequest;//模擬請求
request.Timeout = 30 * 1000;//設置30s超時
request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36";//pc瀏覽器
//request.UserAgent = "Ruanmou Crawler";
//request.UserAgent = "Mozilla / 5.0(iPhone; CPU iPhone OS 7_1_2 like Mac OS X) App leWebKit/ 537.51.2(KHTML, like Gecko) Version / 7.0 Mobile / 11D257 Safari / 9537.53";//手機板瀏覽器
request.ContentType = "text/html; charset=utf-8";// "text/html;charset=gbk";// 
request.Host = "www.jd.com";

request.Headers.Add("Cookie", @"newUserFlag=1; guid=YFT7C9E6TMFU93FKFVEN7TEA5HTCF5DQ26HZ; gray=959782; cid=av9kKvNkAPJ10JGqM_rB_vDhKxKM62PfyjkB4kdFgFY5y5VO; abtest=31; _ga=GA1.2.334889819.1425524072; grouponAreaId=37; provinceId=20; search_showFreeShipping=1; rURL=http%3A%2F%2Fsearch.yhd.com%2Fc0-0%2Fkiphone%2F20%2F%3Ftp%3D1.1.12.0.73.Ko3mjRR-11-FH7eo; aut=5GTM45VFJZ3RCTU21MHT4YCG1QTYXERWBBUFS4; ac=57265177%40qq.com; msessionid=H5ACCUBNPHMJY3HCK4DRF5VD5VA9MYQW; gc=84358431%2C102362736%2C20001585%2C73387122; tma=40580330.95741028.1425524063040.1430288358914.1430790348439.9; tmd=23.40580330.95741028.1425524063040.; search_browse_history=998435%2C1092925%2C32116683%2C1013204%2C6486125%2C38022757%2C36224528%2C24281304%2C22691497%2C26029325; detail_yhdareas=""; cart_cookie_uuid=b64b04b6-fca7-423b-b2d1-ff091d17e5e5; gla=20.237_0_0; JSESSIONID=14F1F4D714C4EE1DD9E11D11DDCD8EBA; wide_screen=1; linkPosition=search");

//request.Headers.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8");
//request.Headers.Add("Accept-Encoding", "gzip, deflate, sdch");
//request.Headers.Add("Referer", "http://list.yhd.com/c0-0/b/a-s1-v0-p1-price-d0-f0-m1-rt0-pid-mid0-kiphone/");
request.Method = "GET";
//Encoding enc = Encoding.GetEncoding("GB2312"); // 如果是亂碼就改成 utf-8 / GB2312

#region Post
//int sort = 2;//人數
//string dataString = string.Format("k={0}&n=24&st={1}&iso=0&src=1&v=4093&p={2}&isRecommend=false&city_id=0&from=1&ldw=1361580739", keyword, sort, 1);
//Encoding encoding = Encoding.UTF8;//根據網站編碼自訂義
//byte[] postData = encoding.GetBytes(dataString);
//request.ContentLength = postData.Length;
//Stream requestStream = request.GetRequestStream();
//requestStream.Write(postData, 0, postData.Length);
#endregion

Encoding enc = Encoding.UTF8;//.GetEncoding("GB2312");
using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)//發起請求
{
    if (response.StatusCode != HttpStatusCode.OK)
    {
        logger.Warn(string.Format("抓取{0}地址返回失敗,response.StatusCode為{1}", url, response.StatusCode));
    }
    else
    {
        try
        {
            StreamReader sr = new StreamReader(response.GetResponseStream(), enc);
            html = sr.ReadToEnd();//讀取數據
            sr.Close();
        }
        catch (Exception ex)
        {
            logger.Error(string.Format($"DownloadHtml抓取{url}失敗"), ex);
            html = null;
        }
    }
}
return html

日誌紀錄(Log4Net)

<?xml version="1.0" encoding="utf-8"?>
<log4net>
  <!-- Define some output appenders -->
  <appender name="rollingAppender" type="log4net.Appender.RollingFileAppender">
    <file value="log\log.txt" />

    <!--追加日誌內容-->
    <appendToFile value="true" />

    <!--防止多線程時不能寫Log,官方說線程非安全-->
    <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />

    <!--可以為:Once|Size|Date|Composite-->
    <!--Composite為=為Size和Date的組合-->
    <rollingStyle value="Composite" />

    <!--當備份文件時,為文件名加的後綴-->
    <datePattern value="yyyyMMdd.TXT" />

    <!--日誌最大個數,都是最新的-->
    <!--rollingStyle節點為Size時,只能有value個日誌-->
    <!--rollingStyle節點為Composite時,每天有value個日誌-->
    <maxSizeRollBackups value="20" />

    <!--可用的單位:KB|MB|GB-->
    <maximumFileSize value="3MB" />

    <!--設置為true,當前最新日誌文件名永遠為file節中的名字-->
    <staticLogFileName value="true" />

    <!--輸出級別在INFO和ERROR之間的日誌-->
    <filter type="log4net.Filter.LevelRangeFilter">
      <param name="LevelMin" value="INFO" />
      <param name="LevelMax" value="FATAL" />
    </filter>

    <layout type="log4net.Layout.PatternLayout">
      <conversionPattern value="%date [%thread] %-5level %logger - %message%newline"/>
    </layout>
  </appender>

  <!-- levels: OFF > FATAL > ERROR > WARN > INFO > DEBUG  > ALL -->
  <root>
    <priority value="ALL"/>
    <level value="ALL"/>
    <appender-ref ref="rollingAppender" />
  </root>
</log4net>

static Logger()
{
    XmlConfigurator.Configure(new FileInfo(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "CfgFiles\\log4net.cfg.xml")));
    ILog Log = LogManager.GetLogger(typeof(Logger));
    Log.Info("系統初始化Logger模塊");
}

private ILog loger = null;
public Logger(Type type)
{
    loger = LogManager.GetLogger(type);
}

loger.Error(msg, ex);
loger.Warn(msg);
loger.Info(msg);
loger.Debug(msg);

解析HTML資料(HtmlAgiliytyPack)

1. 透過正則表達式搭配Substring/indexof/replace
2. HtmlAgiliytyPack；基於Xpath解析

Xpath

1. 假設要找這段文字的Xpath，先找到它的HTML位置
   📷
2. 再對它的位置點右鍵=>Copy => CopyXPath
   📷
3. 再透過XPath Helper 套件，可以驗證剛剛複製的XPath的路徑，是否正確
   📷

HtmlAgiliytyPack用法

1. 新增HtmlDocument物件
2. 使用LoadHtml存進HtmlDocument物件
3. 使用SelectNodes找尋Xpath節點內容

public void Crawl()
{
    //下載HTML
    string html = HttpHelper.DownloadHtml("https://www.jd.com/allSort.aspx");
    if (string.IsNullOrEmpty(html))
    {
        //需要重試。記錄下來
    }
    HtmlDocument document = new HtmlDocument();
    document.LoadHtml(html);
    {
        //Xpath路徑
        string secondPath = "//dl/dt/a";
        HtmlNodeCollection nodeList = document.DocumentNode.SelectNodes(secondPath);//找多個節點
        if (nodeList != null)
        {
            foreach (HtmlNode node in nodeList)
            {
                string url = node.Attributes["href"].Value;
                string name = node.InnerText;
            }
        }
    }          
}

參考資料