javaweb-day02-3（XML 解析 - Dom4j解析开发包 - XPath）

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本文介绍了如何结合Dom4j API和XPath表达式方便地获取XML节点，并提供了XPath快速入门指南。通过示例展示了如何利用XPath选择多个和单个节点。还涉及到学生成绩管理系统重构的实践，包括需求分析、模块流程和开发顺序，强调了代码组织结构的重要性。

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由于dom4j在获取某个节点时都得一级一级往下获，很不方便。

由于XPath表达式，获取某个节点很方便直观，所以就要由dom4j API 结合XPath表达式来获取节点，然后对节点进行某些操作。

XPath快速入门，查看官方帮助文档：XPathTutorial.chm
dom4j API 与XPath的结合，要看dom4j的docs里面的Quick Start：Powerful Navigation with XPath
获取多个节点：Listlist = document. selectNodes ("//foo/bar");
获取单个节点：Nodenode = document. selectSingleNode ("//foo/bar/author");

创建XPath需要jaxen.jar包的支持。如没有导入可能会报错：java.lang.NoClassDefFoundError: org/jaxen/JaxenException

练习一：

book.xml

<?xml version="1.0" encoding="UTF-8"?>

<书架> 
  <书 name="yyyYYY"> 
    <书名>Java就业培训教程</书名>  
    <售价>999</售价>  
    <售价>999</售价>  
    <作者>张孝祥</作者>  
    <售价>20元</售价>  
    <售价>20元</售价>
  </书>  
  <书> 
    <书名>JavaScript网页开发</书名>  
    <作者>张孝祥</作者>  
    <售价>28.00元</售价> 
  </书> 
</书架>

//获取第二个书名的值

	@Test
	public void findwithXpath() throws DocumentException{
		SAXReader reader = new SAXReader();
		Document document = reader.read("src/book.xml");
		
		//获取第二个书名的值
		Element ele = (Element)document.selectNodes("//书名").get(1);
		System.out.println(ele.getText());
	}

练习二：

users.xml

<?xml version="1.0" encoding="UTF-8"?>

<users>
	<user username="lisi" password="123"></user>
	<user username="wanghong" password="123"></user>
	<user username="hehe" password="123"></user>
</users>

//用户登录

	@Test
	public void login() throws DocumentException{
		SAXReader reader = new SAXReader();
		Document document = reader.read("src/users.xml");
		
		String username = "lisi";
		String password = "123";
		
		Node node = document.selectSingleNode("//user[@username='"+username+"' and @password='"+password+"']");
		if(node != null){
			System.out.println("登录成功！");
		}else{
			System.out.println("用户名或密码错误......");
		}
		
	}

练习三：用dom4j做学生成绩管理系统的重构

需求分析：

1、以如下格式的exam.xml文件为例

exam.xml

<?xml version="1.0" encoding="UTF-8"?>

<exam> 
  <student examid="222" idcard="111"> 
    <name>张三</name>  
    <location>沈阳</location>  
    <grade>89.00</grade> 
  </student>  
  <student examid="444" idcard="333"> 
    <name>李四</name>  
    <location>大连</location>  
    <grade>97.00</grade> 
  </student> 
</exam>

２、编程实现如下功能

３、实现学生信息的添加

４、实现学生信息的查询

５、实现学生的删除功能

模块流程图：

添加数据：

查询数据：

开发顺序：

先写javabean，再写Dao用到的工具类、 Dao ，最后写界面层Main。

不同模块的程序，要放在不同的包里：

实体javabean：放在domain包。
Dao：放在dao包。dao操作xml文档必定会有重复代码：得到document、更新xml文档。将他们抽取到工具类XmlUtils里。
工具类XmlUtils：放在utils工具包中。
界面Main：放在main包。

程序源码：

package cn.mengmei.domain;

public class Student {
	private String idcard;
	private String examid;
	private String name;
	private String location;
	private double grade;
	
	public String getIdcard() {
		return idcard;
	}
	public void setIdcard(String idcard) {
		this.idcard = idcard;
	}
	public String getExamid() {
		return examid;
	}
	public void setExamid(String examid) {
		this.examid = examid;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getLocation() {
		return location;
	}
	public void setLocation(String location) {
		this.location = location;
	}
	public double getGrade() {
		return grade;
	}
	public void setGrade(double grade) {
		this.grade = grade;
	}
}

package cn.mengmei.utils;

import java.io.FileOutputStream;
import java.io.IOException;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;

public class XMLUtils {
	
	public static Document getDocument() throws DocumentException{
		SAXReader reader = new SAXReader();
		Document document = reader.read("src/exam.xml");
		return document;
	}
	
	public static void write2XML(Document document) throws IOException{
		OutputFormat format = OutputFormat.createPrettyPrint();
		format.setEncoding("UTF-8");
		XMLWriter writer = new XMLWriter(new FileOutputStream("src/exam.xml"),format);
		writer.write(document);
		writer.close();
	}
	
}

package cn.mengmei.dao;

import java.util.Iterator;
import java.util.List;

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

import cn.mengmei.domain.Student;
import cn.mengmei.utils.XMLUtils;

public class StudentDao {

	public void add(Student student){
		try {
			Document document = XMLUtils.getDocument();
			Element root = document.getRootElement();
			
			Element stuNode = root.addElement("student");
			stuNode.addAttribute("idcard", student.getIdcard());
			stuNode.addAttribute("examid", student.getExamid());
			stuNode.addElement("name").setText(student.getName());
			stuNode.addElement("location").setText(student.getLocation());
			stuNode.addElement("grade").setText(student.getGrade()+"");
			
			XMLUtils.write2XML(document);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
	
	public void delete(String name){
		try {
			Document document = XMLUtils.getDocument();
			List<Node> nameList = document.selectNodes("//name");
			
			for(Iterator<Node> it=nameList.iterator(); it.hasNext(); ){
				Node nameNode = it.next();
				if(nameNode.getText().equals(name)){
					Node stuNode = nameNode.getParent();
					stuNode.getParent().remove(stuNode);
					XMLUtils.write2XML(document);
					return;
				}
			}
			throw new RuntimeException("------对不起，没有查到此学生！-----");
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
	
	public Student read(String examid){
		
		try{
			Document document = XMLUtils.getDocument();
			
			Element stuNode = (Element)document.selectSingleNode("//student[@examid='"+examid+"']");
			if(stuNode != null){
				Student student = new Student();
				student.setIdcard(stuNode.attributeValue("idcard"));
				student.setExamid(stuNode.attributeValue("examid"));
				student.setName(stuNode.elementText("name"));
				student.setLocation(stuNode.elementText("location"));
				student.setGrade(Double.parseDouble(stuNode.elementText("grade")));
				return student;
			}
			return null;
			
		}catch(Exception e){
			throw new RuntimeException(e);
		}
	}
}

package cn.mengmei.main;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import cn.mengmei.dao.StudentDao;
import cn.mengmei.domain.Student;

public class Main {

	public static void main(String[] args) {

		System.out.println("添加用户：(a)       删除用户：(b)       查询成绩：(c)");
		System.out.print("请输入操作类型：");
		BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
		String item = null;
		try {
			item = reader.readLine();
		} catch (IOException e) {
			System.out.println("-----------类型读取失败！---------");
		}
		
		Student student = null;
		String idcard = null;
		String examid = null;
		String name = null;
		String location = null;
		String grade = null;
		StudentDao dao = null;
		
		switch (item) {
		
		case "a":
			try{
				System.out.print("请输入学生姓名：");
				name = reader.readLine();
				System.out.print("请输入学生身份证号：");
				idcard = reader.readLine();
				System.out.print("请输入学生准考证号：");
				examid = reader.readLine();
				System.out.print("请输入学生所在地：");
				location = reader.readLine();
				System.out.print("请输入学生成绩：");
				grade = reader.readLine();
				
				student = new Student();
				student.setName(name);
				student.setIdcard(idcard);
				student.setExamid(examid);
				student.setLocation(location);
				student.setGrade(Double.parseDouble(grade));
				
				dao = new StudentDao();
				dao.add(student);
				
				System.out.println("--------添加数据成功--------");
			}catch(Exception e){
				System.out.println("---------对不起，添加失败！---------");
			}
			break;
			
		case "b":
			try{
				System.out.print("请输入要删除的学生姓名：");
				name = reader.readLine();
				dao = new StudentDao();
				dao.delete(name);
				System.out.println("------已成功删除学生信息------");
			}catch(Exception e){
				System.out.println(e.getMessage());
			}
			break;
			
		case "c":
			try {
				System.out.print("请输入要查询的学生准考证号：");
				examid = reader.readLine();
				dao = new StudentDao();
				student = dao.read(examid);
				if(student != null){
					System.out.println("姓名："+student.getName());
					System.out.println("身份证号："+student.getIdcard());
					System.out.println("准考证号："+student.getExamid());
					System.out.println("所在地："+student.getLocation());
					System.out.println("成绩："+student.getGrade());
				}else{
					System.out.println("-----对不起，你要查询的学生信息不存在！-----");
				}
			} catch (Exception e) {
				System.out.println("------对不起，查询失败！------");
			}
			break;

		default:
			System.out.println("------对不起，不支持此种操作类型！------");
			break;
		}
	}

}