public class Dom4j_ {
    /**
     * 指定读取第一个学生的信息 就是 dom4j+xpath
     */
    @Test
    public void readOne() throws DocumentException {

        //得到一个解析器
        SAXReader reader = new SAXReader();
        //老师的代码技巧->debug 看看document对象的属性
        //分析了document对象的底层结构
        Document document = reader.read(new File("src/students.xml"));

        //1. 得到rootElement, 你是OOP
        Element rootElement = document.getRootElement();

        //2. 获取第一个学生
        Element student = (Element) rootElement.elements("student").get(0);
        //3. 输出该信息
        System.out.println("该学生的信息= " + student.element("name").getText() + " " +
                student.element("age").getText() + " " + student.element("resume").getText() +
                student.element("gender").getText());

        //4. 获取student元素的属性
        System.out.println("id= " + student.attributeValue("id"));
    }
}

dom4j增删改

• 添加

    /*添加一个学生节点到xml文件中*/
    @Test
    public void add() throws DocumentException, IOException {
        //1.拿到解析器
        SAXReader reader = new SAXReader();
        //2.指定解析哪个Xml文件
        Document document = reader.read(new File("src/students.xml"));

        //3.首先创建一个学生节点对象
        Element student = DocumentHelper.createElement("student");
        // 创建name, age, gender子节点
        Element student_name = DocumentHelper.createElement("name");
        Element student_age = DocumentHelper.createElement("age");
        Element student_gender = DocumentHelper.createElement("gender");
        // 如何给元素添加属性
        student.addAttribute("id", "003");
        student_name.setText("威震天");
        student_age.setText("40000");
        student_gender.setText("机器族");

        //4.把三个子元素添加到student节点下
        student.add(student_name);
        student.add(student_age);
        student.add(student_gender);
        // 再把student节点挂载到rootElement下
        document.getRootElement().add(student);

        // 直接输出会中文乱码
        OutputFormat outputFormat = OutputFormat.createPrettyPrint();
        outputFormat.setEncoding("utf-8");

        //5.使用到IO编程 文件字节输出流
        XMLWriter Writer =
                new XMLWriter(new FileOutputStream(new File("src/students.xml")), outputFormat);
        Writer.write(document);
        Writer.close();
    }

删除

    /*删除元素 删除最后一个学生信息*/
    @Test
    public void delete() throws DocumentException, IOException {
        //1.拿到解析器
        SAXReader reader = new SAXReader();
        //2.指定解析哪个Xml文件
        Document document = reader.read(new File("src/students.xml"));
        //3.找到最后一个学生节点
        Element student = (Element) document.getRootElement().elements("student").get(2);
        //拿到父节点 删除元素
        student.getParent().remove(student);

        //直接输出会中文乱码
        OutputFormat output = OutputFormat.createPrettyPrint();
        output.setEncoding("utf-8");
        //更新Xml文件
        XMLWriter writer = new XMLWriter(
                new FileOutputStream(new File("src/students.xml")), output);
        writer.write(document);
        writer.close();
    }

修改

/*修改元素(所有元素的age+3)*/
    @Test
    public void update() throws DocumentException, IOException {
        //1.拿到解析器
        SAXReader reader = new SAXReader();
        //2.指定解析哪个Xml文件
        Document document = reader.read(new File("src/students.xml"));
        //3.拿到所有的student元素
        List<Element> students = document.getRootElement().elements("student");
        //遍历
        for (Element student : students) {
            //设置所有学生的年龄
            Element age = student.element("age");
            age.setText(Integer.parseInt(age.getText()) + 3 + "");
        }
        //直接输出会中文乱码
        OutputFormat output = OutputFormat.createPrettyPrint();
        output.setEncoding("utf-8");
        //4.IO流 文件字节输出流
        XMLWriter writer = new XMLWriter(
                new FileOutputStream(new File("src/students.xml")), output);
        writer.write(document);
        writer.close();
    }

作业

public class Homework {
    public static void main(String[] args) throws DocumentException {

        //1.得到解析器
        SAXReader saxReader = new SAXReader();
        //2.指定解析哪个xml文件
        Document document = saxReader.read(new File("src/books.xml"));

        //3.遍历所有的book元素
        List<Element> books = document.getRootElement().elements("book");
        for (Element book : books) {
            //取出book元素的所有信息
            Element name = book.element("name");
            Element author = book.element("author");
            Element price = book.element("price");
            String id = book.attributeValue("id");
            //创建成Book对象
            Book book1 = new Book();
            book1.setId(Integer.parseInt(id));
            book1.setName(name.getText());
            book1.setPrice(Double.parseDouble(price.getText()));
            book1.setAuthor(author.getText());
            System.out.println("book1对象信息= " + book1);
        }
    }
}