XML 文档解析及 XPath 语言

DOM文档对象模型

• DOM（Document Object Model）定义了访问和操作XML文档的标准方法，DOM把XML文档作为树结构来查看，能够通过DOM树来读写所有元素。

Dom4j

• 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
• 下载Dom4j.jar：链接
• 安装如下图所示

利用Dom4j遍历XML

package week11.dom4j;
import java.util.List;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
public class HrReader {
    public void readXml(){
        String file = ".\\week11\\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<Element> 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");
                String empName = name.getText();//getText()方法用于获取标签文本
                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.element("dname").getText());
                System.out.println(department.element("address").getText());
                Attribute att = employee.attribute("no");
                System.out.println(att.getText());
            }
        } catch (DocumentException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        HrReader reader = new HrReader();
        reader.readXml();
    }
}

利用Dom4j更新XML

package week11.dom4j;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
public class HrWriter {
    public void writeXml(){
        String file = ".\\week11\\hr.xml";
        SAXReader reader = new SAXReader();
        try {
            Document 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("37");
            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) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        HrWriter hrWriter = new HrWriter();
        hrWriter.writeXml();
    }
}

XPath

路径表达式

• XPath路径表达式是XML文档中查找数据的语言
• 掌握XPath可以极大可能的提高在提取数据时的开发效率

• 学习XPath本质就是掌握各种形式表达式的使用技巧

  XPath基本表达式

  
  
  

  Jaxen介绍

• Jaxen是一个Java编写的开源的XPath库。可以适应多种不同对象的模型，如

  • DOM
  • XOM
  • Dom4j
  • JDOM
• Dom4j底层依赖Jaxen实现XPath查询
• Jaxen下载地址
• 安装如下图所示

package week11.dom4j;
import java.util.List;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.Node;
import org.dom4j.io.SAXReader;
public class XPathTestor {
    public void xpath(String xpathExp){
        String file = ".\\week11\\hr.xml";
        SAXReader reader = new SAXReader();
        try {
            Document document = reader.read(file);
            List<Node> 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) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
        XPathTestor testor = new XPathTestor();
//        testor.xpath("/hr/employee");
//        testor.xpath("//employee");
//        testor.xpath("//employee[salary<4000]");
//        testor.xpath("//employee[name='李铁柱']");
//        testor.xpath("//employee[@no=3304]");
//        testor.xpath("//employee[1]");
//        testor.xpath("//employee[last()]");
        //testor.xpath("//employee[position()<3]");
        testor.xpath("//employee[3] | //employee[8]");
    }
}

编程练习一

使用Dom4j操作存储课程信息的plan.xml文件：

1. 为plan.xml文件添加一条新的课程信息

2. 遍历plan.xml文件并将节点和属性等内容输出

   编程练习二

   利用XPath对存储课程信息的plan.xml文档进行查询并将结果输出，要求如下：

3. 获取所有课程信息

4. 查询课时小于50的课程信息
5. 查询课程名为高等数学的课程信息
6. 查询属性id为001的课程信息
7. 查询前两条课程信息