环境：

myeclipse 10

window 10

导入包：dom4j-1.6.1.jar jaxen-1.1-beta-6.jar

代码实现：

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

<student> 
  <stu> 
    <id>100</id>  
    <name>张三</name>  
    <age>20</age> 
  </stu>  
  <stu> 
    <id>101</id>  
    <name>李四</name>  
    <age>30</age> 
  </stu> 
</student>

package com.java.xml;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.List;

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

public class StudentService {
	/**
	 * 增加	添加学生信息
	 * @param student
	 * @throws DocumentException 
	 * @throws IOException 
	 */
	public static void addStudent(Student student) throws DocumentException,IOException {
		/*
		 * 1.创建解析器
		 * 2.得到document
		 * 3.获取根节点
		 * 4.在根节点上面创建stu标签
		 * 5.在stu标签上面创建id name age
		 * 6.分别给id name age元素赋值
		 * 7.回写xml
		 */
		//创建解析器
		SAXReader saxReader = new SAXReader();
		//得到Document
		Document document = saxReader.read("src/student.xml");
		//获取根节点
		Element root = document.getRootElement();
		//在根节点上面添加stu标签
		Element stu = root.addElement("stu");
		//在stu上面添加id name age
		Element id = stu.addElement("id");
		Element name = stu.addElement("name");
		Element age = stu.addElement("age");
		//分别给id name age元素赋值
		id.setText(student.getId());
		name.setText(student.getName());
		age.setText(String.valueOf(student.getAge()));
		//回写xml
		OutputFormat format = OutputFormat.createPrettyPrint();
		XMLWriter xmlWriter = new XMLWriter(new FileOutputStream("src/student.xml"),format);
		xmlWriter.write(document);
		xmlWriter.close();
	}
	/**
	 * 删除 根据id删除学生
	 * @param id
	 * @throws DocumentException 
	 * @throws IOException 
	 */
	public static void deleteStudent(String id) throws DocumentException,IOException {
		/*
		 * 1.创建解析器
		 * 2.得到document
		 * 3.获取所有的id，使用xpath //id 返回 list集合
		 * 4.遍历list集合
		 * 5.判断集合里面的id和传递的id是否相同
		 * 6.如果相同把id所在的stu删除
		 * 7.回写xml
		 */
		//创建解析器
		SAXReader saxReader = new SAXReader();
		//得到document
		Document document = saxReader.read("src/student.xml");
		//获取所有的id
		List<Node> list = document.selectNodes("//id");
		//遍历list集合
		for (Node node : list) {
			//node是每一个id的元素,得到id的值
			String value = node.getText();
			//判断value与传递的id是否相同
			if(value.equals(id)) {
				//id相同，得到stu标签
				Element stu = node.getParent();
				//获取stu的父节点
				Element student = stu.getParent();
				//删除stu
				student.remove(stu);
			}
		}
		//回写xml
		OutputFormat format = OutputFormat.createPrettyPrint();
		XMLWriter xmlWriter = new XMLWriter(new FileOutputStream("src/student.xml"),format);
		xmlWriter.write(document);
		xmlWriter.close();
	}
	/**
	 * 查询 根据id查询学生信息
	 * @param id
	 * @throws DocumentException 
	 */
	public static Student getStudent(String id) throws DocumentException {
		/*
		 * 1.创建解析器
		 * 2.得到document
		 * 3.获取所有的id，返回list集合
		 * 4.遍历list集合
		 * 5.得到每一个id的节点
		 * 6.得到id的节点值
		 * 7.判断id的值与传递的值是否相同
		 * 8.如果相同，先获取到父节点stu
		 * 9.通过stu获取到name，age
		 */
		//创建解析器
		SAXReader saxReader = new SAXReader();
		//得到document
		Document document = saxReader.read("src/student.xml");
		//获取所有的id，得到集合list
		List<Node> list = document.selectNodes("//id");
		//创建Student对象
		Student student = new Student();
		//遍历集合list
		for (Node node : list) {
			//node是每一个id节点,得到id节点的值
			String value = node.getText(); 
			//判读值是否与传入的相同
			if(value.equals(id)) {
				//得到id的父节点
				Element stu = node.getParent();
				//通过stu获取name，age
				String name = stu.element("name").getText();
				String age = stu.element("age").getText();
				student.setId(value);
				student.setName(name);
				student.setAge(Integer.parseInt(age));
			}
		}
		return student;
	}
	
}

package com.java.xml;

import java.io.IOException;

import org.dom4j.DocumentException;

public class StudentCRUD {

	public static void main(String[] args) throws DocumentException,IOException {
//		addStudent();
//		deleteStudent("102");
		getStudent("101");
	}
	
	public static void addStudent() throws DocumentException,IOException {
		Student student = new Student();
		student.setId("102");
		student.setName("王五");
		student.setAge(35);
		StudentService.addStudent(student);
	}
	
	public static void deleteStudent(String id) throws DocumentException,IOException {
		StudentService.deleteStudent(id);
	}
	
	public static void getStudent(String id) throws DocumentException {
		Student student = StudentService.getStudent(id);
		System.out.println(student);
	}
}