java 利用jousp 爬取知乎首页问题

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;
import java.io.IOException;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.nodes.Element;
import org.jsoup.select.Elements;

public class worm0{
    public static void main(String[] args) throws IOException {
    
        Document document=Jsoup.connect("https://www.zhihu.com/").get();
        Elements main=document.select(".ContentLayout-mainColumn");
        
        Elements url=main.select("h2[class=ContentItem-title]").select("a");
        System.out.println("url"+url);
        for(Element question:url){
            //输出href后的值，即主页上每个关注问题的链接
            String URL=question.attr("abs:href");
            //下载问题链接指向的页面
            Document document2=Jsoup.connect(URL).get();
            //问题
            Elements title=document2.select(".QuestionHeader-title");
            //问题描述
            Elements detail=document2.select("span[class=RichText ztext]");
            //回答
            Elements answer=document2.select(".RichContent-inner");
            System.out.println("\n"+"链接："+URL
                    +"\n"+"标题："+title.text()
                    +"\n"+"问题描述："+detail.text()
                    +"\n"+"回答："+answer.text());
        }   
    }
}