获取节点的代码出现了问题！老师求助

# 具体遇到的问题

老师 这里获取节点的代码好像出现了问题！List <Node> nodes = document.selectNodes("/root/category");这条代码报错了！

# 报错信息的截图

# 相关课程内容截图

# 尝试过的解决思路和结果

# 粘贴全部相关代码，切记添加代码注释（请勿截图）

在这里输入代码，可通

package com.imooc.library.utils;

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.util.ArrayList;
import java.util.List;

import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.Node;
import org.dom4j.io.SAXReader;

import com.imooc.library.entity.Book;
import com.imooc.library.entity.Category;
import com.imooc.library.entity.User;

/**
 * 数据源类 解析XML
 * 
 * @author zjczbq
 *
 */
public class XmlDataSource {
	private static List<User> userData = new ArrayList();
	private static List<Category> categoryData = new ArrayList();
	private static List<Book> bookData = new ArrayList();
	private static String userDataFile;
	private static String categoryDataFile;
	private static String bookDataFile; //保存图书的文件地址
	static {
		// 下面代码意思是：在程序运行以后去得到类路径目录下的book.xml文件的路径地址
//		bookDataFile = XmlDataSource.class.getResource("/book.xml").getPath();
//		System.out.println(bookDataFile);
		categoryDataFile = XmlDataSource.class.getResource("/category.xml").getPath();
		System.out.println(categoryDataFile);
		reloadUser();
		reloadCategory();
//		reloadBooks();
	}
	private static void reloadUser() {

	}

	private static void reloadCategory() {
		URLDecoder decoder = new URLDecoder();
		try {
			categoryDataFile = decoder.decode(categoryDataFile, "UTF-8");
			System.out.println(categoryDataFile);
			SAXReader reader = new SAXReader();
			Document document = reader.read("file:///"+categoryDataFile);
			List <Node> nodes = document.selectNodes("/root/category");
			categoryData.clear();
			for(Node node : nodes) {
				Element element = (Element)node;
				Category category = new Category();
				category.setCategoryId(element.elementText("categoryId"));
				category.setCategoryName(element.elementText("categoryName"));
				categoryData.add(category);
				System.out.println(category);
			}
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	private static void reloadBooks() {
		URLDecoder decoder = new URLDecoder();
		try {
			bookDataFile = decoder.decode(bookDataFile, "UTF-8");
			System.out.println(bookDataFile);
			SAXReader reader = new SAXReader();
			// 1.获取Document文档对象
			// 如果文件目录含有中文！可以在加载文件时，前边加上 file:/// 。
			Document document = reader.read("file:///"+bookDataFile);
			//2.Xpath得到XML节点集合
			List<Node> nodes = document.selectNodes("/root/book");
			// Node是所有类型XML节点的统称，Element则通常指的是XML中的标签以及标签中所指代的信息
			bookData.clear();
			for(Node node : nodes) {
				Element element = (Element)node;
				Book book = new Book();
				book.setBookId(Integer.parseInt(element.elementText("bookId")));
				book.setBookName(element.elementText("bookName"));
				book.setBookCategory(element.elementText("bookCategory"));
				book.setBookPrice(Integer.parseInt(element.elementText("bookPrice")));
				book.setBookCover(element.elementText("preview"));
				book.setBookDescription(element.elementText("description"));
				bookData.add(book);
				//System.out.println(book);
			}
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public static void main(String[] args) {
		new XmlDataSource();
	}
}

过选择【代码语言】突出显示

<?xml version="1.0" encoding="UTF-8"?>
<!-- 图书数据 -->
<root>
    <book id="1"> <!-- 图书序号 -->
        <bookId>book0001</bookId>
        <bookName>Java基础</bookName>
        <bookCategory>ca0001</bookCategory>
        <bookPrice>29</bookPrice>
        <preview>/image/g1.jpg</preview>
        <description></description>
    </book>
</root>

<?xml version="1.0" encoding="UTF-8"?>
<root>
    <category id="1"> <!-- 图书分类序号 -->
        <categoryId>ca0001</categoryId>
        <categoryName>计算机</categoryName>
    </category>
</root>

package com.imooc.library.entity;

public class Book {

	private Integer bookId; //图书ID
	private String bookName; //图书名
	private String bookCategory; //图书分类
	private Integer bookPrice; //图书价格
	private String bookCover; //图书封面地址
	private String bookDescription; //图书备注

	public Book() {

	}
	public Book(Integer bookId, String bookName, String bookCategory, Integer bookPrice, String bookCover,
			String bookDescription) {
		super();
		this.bookId = bookId;
		this.bookName = bookName;
		this.bookCategory = bookCategory;
		this.bookPrice = bookPrice;
		this.bookCover = bookCover;
		this.bookDescription = bookDescription;
	}

	public Integer getBookId() {
		return bookId;
	}
	public void setBookId(Integer bookId) {
		this.bookId = bookId;
	}
	public String getBookName() {
		return bookName;
	}
	public void setBookName(String bookName) {
		this.bookName = bookName;
	}
	public String getBookCategory() {
		return bookCategory;
	}
	public void setBookCategory(String bookCategory) {
		this.bookCategory = bookCategory;
	}
	public Integer getBookPrice() {
		return bookPrice;
	}
	public void setBookPrice(Integer bookPrice) {
		this.bookPrice = bookPrice;
	}
	public String getBookCover() {
		return bookCover;
	}
	public void setBookCover(String bookCover) {
		this.bookCover = bookCover;
	}
	public String getBookDescription() {
		return bookDescription;
	}
	public void setBookDescription(String bookDescription) {
		this.bookDescription = bookDescription;
	}
	@Override
	public String toString() {
		return "Book [bookId=" + bookId + ", bookName=" + bookName + ", bookCategory=" + bookCategory + ", bookPrice="
				+ bookPrice + ", bookCover=" + bookCover + ", bookDescription=" + bookDescription + "]";
	}

}

package com.imooc.library.entity;

/**
 * JavaBeen
 * 
 * @author zjczbq
 *
 */
public class Category {
	private String categoryId; //图书分类id
	private String categoryName;  //分类名称

	public Category() {

	}

	public Category(String categoryId, String categoryName) {
		super();
		this.categoryId = categoryId;
		this.categoryName = categoryName;
	}

	public String getCategoryId() {
		return categoryId;
	}

	public void setCategoryId(String categoryId) {
		this.categoryId = categoryId;
	}

	public String getCategoryName() {
		return categoryName;
	}

	public void setCategoryName(String categoryName) {
		this.categoryName = categoryName;
	}

	@Override
	public String toString() {
		return "Category [categoryId=" + categoryId + ", categoryName=" + categoryName + "]";
	}

}