XML

XML支持五种实体引用:
< < 小于
> > 大于
& & 和号
' ‘ 单引号
" “ 双引号

CDATA标签：指的是不应有XML解析器进行解析的文本数据
格式：

XML语义约束方式：DTD文(文档类型定义,扩展名为.dtd)与XML Schema
XML引用DTD文件格式：
hehe.dtd

hehe.xml

    
        张三
        31
        4000
        
            会计部
            
xx大厦-B103
        
    

XML Schema比DTD更为复杂，提供了更多功能

hehe.xsd

hehe.xml

    
        张三
        31
        4000
        
            会计部
            
XX大厦-B103
        
    
    
        李四
        23
        3000
        
            工程部
            
XX大厦-B104
        
    

DOM文档对象模型
Dom4j是一个易用的、开源的库,用于解析XML。它应用于Java平台,具有性能优异、功能强大和极其易使用的特点。
Dom4j将XML视为Document对象。
XML标签被Dom4j定义为Element对象。

读取XML文件

public class TestXml {
    public void readXml(){
        String file = "/Users/jxb/Desktop/java/xml/src/main/resources/hr.xml";
        //SAXReader类是读取XML文件的核心类，用于将XML解析后以"树"的形式保存在内存中；
        SAXReader reader = new SAXReader();
        try {
            Document document = reader.read(file);
            //获取XML文档的根节点，即hr标签
            Element root = document.getRootElement();
            //elements方法用于获取指定的标签集合
            List employees = root.elements("employee");
            for (Element employee : employees) {
                //element方法用于获取唯一的子节点对象
                Element name = employee.element("name");
                //getText方法用户获取标签文本
                String empName = name.getText();
                System.out.println(empName);

                System.out.println(employee.elementText("age"));
                System.out.println(employee.elementText("salary"));

                Element department = employee.element("department");
                System.out.println(department.elementText("dname"));
                System.out.println(department.elementText("address"));

                Attribute attribute = employee.attribute("no");
                System.out.println(attribute.getText());
            }

        } catch (DocumentException e) {
            throw new RuntimeException(e);
        }
    }

    public static void main(String[] args) {
        TestXml testXml = new TestXml();
        testXml.readXml();
    }
}

写入XML文件

public class HrWriter {
    public void writeXml(){

        String file = "/Users/jxb/Desktop/java/xml/src/main/resources/hr.xml";
        SAXReader reader = new SAXReader();

        Document document = null;
        try {
            document = reader.read(file);
            Element root = document.getRootElement();
            Element employee = root.addElement("employee");
            employee.addAttribute("no", "3311");
            Element name = employee.addElement("name");
            name.setText("李铁柱");
            employee.addElement("age").setText("24");
            employee.addElement("salary").setText("3600");
            Element department = employee.addElement("department");
            department.addElement("dname").setText("人事部");
            department.addElement("address").setText("xx大厦-B105");

            Writer writer = new OutputStreamWriter(new FileOutputStream(file), "UTF-8");
            document.write(writer);
            writer.close();

        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static void main(String[] args) {
        HrWriter hrWriter = new HrWriter();
        hrWriter.writeXml();
    }
}

XPath路径表达式

截屏2022-08-11 10.23.31.png

截屏2022-08-11 10.23.45.png

截屏2022-08-11 10.24.09.png

截屏2022-08-11 10.24.55.png

public class XPathTestor {
    public void xpath(String xpathExp) {
        String file = "/Users/aisino/Desktop/java/xml/src/main/resources/hr.xml";
        SAXReader reader = new SAXReader();
        try {
            Document document = reader.read(file);
            List nodes = document.selectNodes(xpathExp);
            for (Node node : nodes) {
                Element emp = (Element) node;
                System.out.println(emp.attributeValue("no"));
                System.out.println(emp.elementText("name"));
                System.out.println(emp.elementText("age"));
                System.out.println(emp.elementText("salary"));
                System.out.println("=============================");
            }
        } catch (DocumentException e) {
            throw new RuntimeException(e);
        }
    }

    public static void main(String[] args) {
        XPathTestor testor = new XPathTestor();
//        testor.xpath("/hr/employee");
//        testor.xpath("//employee");
//        testor.xpath("//employee[salary<3600]");
//        testor.xpath("//employee[name='李铁柱']");
//        testor.xpath("//employee[@no=3311]");
//        testor.xpath("//employee[1]");
//        testor.xpath("//employee[last()]");
//        testor.xpath("//employee[position()<3]");
        testor.xpath("//employee[1] | //employee[3]");
    }
}