C#抓取网页数据 解析标题描述图片等信息 去除HTML标签
一、首先将网页内容整个抓取下来,数据放在byte[]中(网络上传输时形式是byte),进一步转化为String,以便于对其操作,实例如下:
private static string GetPageData(string url)
{
if (url == null || url.Trim() == "")
return null;
WebClient wc = new WebClient();
wc.Credentials = CredentialCache.DefaultCredentials;
Byte[] pageData = wc.DownloadData(url);
return Encoding.Default.GetString(pageData);//.ASCII.GetString
}
二、得到了数据的字符串形式,然后可以对网页进行解析了(其实就是对字符串的各种操作和正则表达式的应用):
常用的的解析还有以下几种:
1.获取标题
Match TitleMatch = Regex.Match(strResponse, "<title>([^<]*)</title>", RegexOptions.IgnoreCase | RegexOptions.Multiline);
title = TitleMatch.Groups[1].Value;
2.获取描述信息
Match Desc = Regex.Match(strResponse, "<meta name=\"DESCRIPTION\" content=\"([^<]*)\">", RegexOptions.IgnoreCase | RegexOptions.Multiline);
strdesc = Desc.Groups[1].Value;
3.获取图片
public class HtmlHelper
{
/// <summary>
/// HTML中提取图片地址
/// </summary>
public static List<string> PickupImgUrl(string html)
{
Regex regImg = new Regex(@"<img\b[^<>]*?\bsrc[\s\t\r\n]*=[\s\t\r\n]*[""']?[\s\t\r\n]*(?<imgUrl>[^\s\t\r\n""'<>]*)[^<>]*?/?[\s\t\r\n]*>", RegexOptions.IgnoreCase);
MatchCollection matches = regImg.Matches(html);
List<string> lstImg = new List<string>();
foreach (Match match in matches)
{
lstImg.Add(match.Groups["imgUrl"].Value);
}
return lstImg;
}
/// <summary>
/// HTML中提取图片地址
/// </summary>
public static string PickupImgUrlFirst(string html)
{
List<string> lstImg = PickupImgUrl(html);
return lstImg.Count == 0 ? string.Empty : lstImg[0];
}
}
4.去除Html标签
private string StripHtml(string strHtml)
{
Regex objRegExp = new Regex("<(.|\n)+?>");
string strOutput = objRegExp.Replace(strHtml, "");
strOutput = strOutput.Replace("<", "<");
strOutput = strOutput.Replace(">", ">");
return strOutput;
}
有些例外会使得去除不干净,所以建议连续两次转化。这样将Html标签转化为了空格。太多连续的空格会影响之后对字符串的操作。所以再加入这样的语句:
//把所有空格变为一个空格
Regex r = new Regex(@"\s+");
wordsOnly = r.Replace(strResponse, " ");
wordsOnly.Trim();