“线程“main”java.Lang.NullPointerException 中的异常”错误
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"Exception in thread "main" java.Lang.NullPointerException" Error
提问by Hen Sapir
I am trying to run a web scraper in Eclipse that, using Jsoup, that can take the names of the professors on this page: yu.edu/faculty and print them out. This is my code:
我正在尝试在 Eclipse 中运行一个网络抓取工具，使用 Jsoup，它可以获取此页面上教授的姓名：yu.edu/faculty 并将它们打印出来。这是我的代码：
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 YUscraper {
public static void main(String[] args) throws IOException {
// fetches & parses HTML
String url = "http://yu.edu/faculty/";
Document document = Jsoup.connect(url).get();
// Extract data
Element content = document.getElementById("mainlist");
Elements names = content.getElementsByTag("a");
// Output data
for (Element name : names) {
System.out.println("Name: " + name.text());
}
}
}
I am getting this error:
我收到此错误：
Exception in thread "main" java.lang.NullPointerException
at YUscraper.main(YUscraper.java:18)
I am relatively new to this so pardon me if I am missing something really evident. I used many examples I have seen to get to this point, but I still don't understand what throws IOException is for and what it means that an exception was found. Please help, thanks!
我对此比较陌生，所以如果我遗漏了一些非常明显的东西，请原谅我。我使用了很多我见过的例子来达到这一点，但我仍然不明白 throws IOException 是什么以及发现异常意味着什么。请帮忙，谢谢！
采纳答案by Vivek Vermani
Line 18 is
第 18 行是
Elements names = content.getElementsByTag("a");
元素名称 = content.getElementsByTag("a");
Seems like there is no tag with id "mainlist" in the html retrieved from http://yu.edu/faculty/.
从http://yu.edu/faculty/检索到的 html 中似乎没有 id 为“mainlist”的标签。
Seems like you were trying to access tag main-nav instead of mainlist.
似乎您试图访问标签 main-nav 而不是 mainlist。
回答by harshit
Line Element content = document.getElementById("mainlist");
线 Element content = document.getElementById("mainlist");
content is returned as null, so null.getElementsByTagis giving the error .. Looks like html doesn't have element by 'mainlist'
内容返回为空，所以null.getElementsByTag给出错误.. 看起来 html 没有“mainlist”的元素
