Java爬虫怎么实现Jsoup利用dom方法遍历Document对象
本文主要介绍"Java爬虫怎么实现Jsoup利用dom方法遍历Document对象" 有关的知识，希望能够解决您遇到有关问题，下面我们一起来看看这篇 "Java爬虫怎么实现Jsoup利用dom方法遍历Document对象" 文章。
先给出网页地址：
https://wall.alphacoders.com/featured.php?lang=Chinese
主要步骤：
利用Jsoup的connect方法获取Document对象
String html = "https://wall.alphacoders.com/featured.php?lang=Chinese"; Document doc = Jsoup.connect(html).get();
内容过长，就不再显示。
我们以这部分为例：
<ul class="nav nav-pills"> <li><a href="https://alphacoders.com/site/about-us" rel="external nofollow" rel="external nofollow" >About Us</a></li> <li><a href="https://alphacoders.com/site/faq" rel="external nofollow" rel="external nofollow" >FAQ</a></li> <li><a href="https://alphacoders.com/site/privacy" rel="external nofollow" rel="external nofollow" >Privacy Policy</a></li> <li><a href="https://alphacoders.com/site/tos" rel="external nofollow" rel="external nofollow" >Terms Of Service</a></li> <li><a href="https://alphacoders.com/site/acceptable_use" rel="external nofollow" rel="external nofollow" >Acceptable Use</a></li> <li><a href="https://alphacoders.com/site/etiquette" rel="external nofollow" rel="external nofollow" >Etiquette</a></li> <li><a href="https://alphacoders.com/site/advertising" rel="external nofollow" rel="external nofollow" >Advertise With Us</a></li> <li><a id="change_consent">Change Consent</a></li> </ul>
我们先找到所有的ul：
Elements elements = doc.getElementsByTag("ul");
输出如下：
<ul class="nav navbar-nav center"> <li> <a title="Submit Wallpapers" href="https://alphacoders.com/site/submit-wallpaper" rel="external nofollow" ><i class="el el-circle-arrow-up"></i> 提交</a> </li> <li> <a href="https://alphacoders.com/contest" rel="external nofollow" ><i class="el el-gift"></i> 精美奖品</a> </li> </ul> <ul class="nav navbar-nav navbar-right center"> <li> <a href="language.php?lang=Chinese" rel="external nofollow" > <img src="https://cache.yisu.com/upload/information/20220517/112/2427.png" alt="Chinese-flag"> 中文 </a> </li> <li> <a href="https://alphacoders.com/users/login" rel="external nofollow" ><i class="el el-user"></i> 登录</a> </li> <li> <a href="https://alphacoders.com/users/register" rel="external nofollow" ><i class="el el-edit"></i> 注册</a> </li> </ul> <ul class="pagination"> <li class="active"><a id="prev_page" href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >< 上一页</a></li> <li class="active"><a>1</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=2" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >2</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=3" rel="external nofollow" rel="external nofollow" rel="external nofollow" >3</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=4" rel="external nofollow" rel="external nofollow" rel="external nofollow" >4</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=5" rel="external nofollow" rel="external nofollow" rel="external nofollow" >5</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=6" rel="external nofollow" rel="external nofollow" rel="external nofollow" >6</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=7" rel="external nofollow" rel="external nofollow" rel="external nofollow" >7</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=8" rel="external nofollow" >8</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=9" rel="external nofollow" >9</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=10" rel="external nofollow" >10</a></li> <li><a>...</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=319" rel="external nofollow" rel="external nofollow" rel="external nofollow" >319</a></li> <li><a id="next_page" href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=2" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >下一页 ></a></li> </ul> <ul class="pagination"> <li class="active"><a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >< 上一页</a></li> <li class="active"><a>1</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=2" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >2</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=3" rel="external nofollow" rel="external nofollow" rel="external nofollow" >3</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=4" rel="external nofollow" rel="external nofollow" rel="external nofollow" >4</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=5" rel="external nofollow" rel="external nofollow" rel="external nofollow" >5</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=6" rel="external nofollow" rel="external nofollow" rel="external nofollow" >6</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=7" rel="external nofollow" rel="external nofollow" rel="external nofollow" >7</a></li> <li><a>...</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=319" rel="external nofollow" rel="external nofollow" rel="external nofollow" >319</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=2" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >下一页 ></a></li> </ul> <ul class="pagination"> <li class="active"><a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" ><< </a></li> <li class="active"><a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >< 上一页</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=2" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >下一页 ></a></li> <li><a title="末页 (319)" href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=319" rel="external nofollow" rel="external nofollow" rel="external nofollow" > >></a></li> </ul> <ul class="pagination"> <li class="active"><a href="#" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >1</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=2" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >2</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=3" rel="external nofollow" rel="external nofollow" rel="external nofollow" >3</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=4" rel="external nofollow" rel="external nofollow" rel="external nofollow" >4</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=5" rel="external nofollow" rel="external nofollow" rel="external nofollow" >5</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=6" rel="external nofollow" rel="external nofollow" rel="external nofollow" >6</a></li> <li><a href="https://wall.alphacoders.com/featured.php?lang=Chinese&page=7" rel="external nofollow" rel="external nofollow" rel="external nofollow" >7</a></li> </ul> <ul class="nav nav-pills"> <li><a href="https://alphacoders.com/site/about-us" rel="external nofollow" rel="external nofollow" >About Us</a></li> <li><a href="https://alphacoders.com/site/faq" rel="external nofollow" rel="external nofollow" >FAQ</a></li> <li><a href="https://alphacoders.com/site/privacy" rel="external nofollow" rel="external nofollow" >Privacy Policy</a></li> <li><a href="https://alphacoders.com/site/tos" rel="external nofollow" rel="external nofollow" >Terms Of Service</a></li> <li><a href="https://alphacoders.com/site/acceptable_use" rel="external nofollow" rel="external nofollow" >Acceptable Use</a></li> <li><a href="https://alphacoders.com/site/etiquette" rel="external nofollow" rel="external nofollow" >Etiquette</a></li> <li><a href="https://alphacoders.com/site/advertising" rel="external nofollow" rel="external nofollow" >Advertise With Us</a></li> <li><a id="change_consent">Change Consent</a></li> </ul>
可以发现class为"nav nav-pills"的只有一个，我们找到它：
Elements elements = doc.getElementsByTag("ul"); //System.out.println(elements); Element tempElement = null; for(Element element : elements) { if (element.className().equals("nav nav-pills")) { tempElement = element; //System.out.println(element.className()); break; } }
循环遍历这个ul，输出其中每一个li里每一个a的href和rel属性：
Elements li = tempElement.getElementsByTag("li"); for(Element element : li) { Elements element2 = element.getElementsByTag("a"); for(Element element3 : element2) { String hrefString = element3.attr("href"); String relString = element3.attr("rel"); if(hrefString != "" && relString != "") { System.out.println("href=" + hrefString + " rel="external nofollow" rel="external nofollow" " + "rel=" + relString); } } }
最终结果：
href=https://alphacoders.com/site/about-us rel=nofollow
href=https://alphacoders.com/site/faq rel=nofollow
href=https://alphacoders.com/site/privacy rel=nofollow
href=https://alphacoders.com/site/tos rel=nofollow
href=https://alphacoders.com/site/acceptable_use rel=nofollow
href=https://alphacoders.com/site/etiquette rel=nofollow
href=https://alphacoders.com/site/advertising rel=nofollow
完整代码：
import org.jsoup.nodes.Document; import org.jsoup.nodes.Element; import org.jsoup.select.Elements; import java.io.IOException; import org.jsoup.Jsoup; /** * @ClassName: Jsoup_Test * @description: * @author: KI * @Date: 2020年8月17日 下午8:15:14 */ public class Jsoup_Test { public static void main(String[] args) throws IOException { // TODO 自动生成的方法存根 String html = "https://wall.alphacoders.com/featured.php?lang=Chinese"; Document doc = Jsoup.connect(html).get(); System.out.println(doc); Elements elements = doc.getElementsByTag("ul"); //System.out.println(elements); Element tempElement = null; for(Element element : elements) { if (element.className().equals("nav nav-pills")) { tempElement = element; //System.out.println(element.className()); break; } } System.out.println(tempElement); Elements li = tempElement.getElementsByTag("li"); for(Element element : li) { Elements element2 = element.getElementsByTag("a"); for(Element element3 : element2) { String hrefString = element3.attr("href"); String relString = element3.attr("rel"); if(hrefString != "" && relString != "") { System.out.println("href=" + hrefString + " rel="external nofollow" rel="external nofollow" " + "rel=" + relString); } } } } }
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