<?xml version="1.0" encoding="UTF-8"?><Students>
 <student id="2">
 <name>ttt</name>
 <age>44</age>
 </student>
 <student id="3">
 <name>linda2</name>
 <age>22</age>
 </student>
 <student id="4">
 <name>linda3</name>
 <age>23</age>
 </student>
 <student id="5">
 <name>jack</name>
 <age>2</age>
 </student>
 <student id="1">
  <name>yyh1</name>
  <age>22</age>
 </student>
</Students>

import java.io.File;
import java.io.IOException;
import java.util.Scanner;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.TransformerFactoryConfigurationError;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.w3c.dom.Text;
import org.xml.sax.SAXException;

//在学生管理系统里面，学生的学号是唯一的，姓名有可能重复
public class StudentManager {
 public static void main(String[] args) {
  try {
   Document doc = Domutils.getDoc(new File("xml文件的相对路径"));
   Scanner input = new Scanner(System.in);
   System.out.println("欢迎来到学生管理系统\n\n\n请输入你要进行什么操作是：\n1.添加学生信息\n2.删除学生信息\n3.修改学生信息\n(请输入前边的序号)");
   int num = input.nextInt();
   if(num == 1) {
    addStudent(doc);
   }else if(num == 2) {
    delStudent(doc);
   }else if(num == 3) {
    updStudent(doc);
   }
  } catch (SAXException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  } catch (ParserConfigurationException e) {
   e.printStackTrace();
  }
 }
 //修改学生信息
 private static void updStudent(Document doc) {
  Element updStudent = null;
  Scanner input = new Scanner(System.in);
  System.out.println("请输入你要修改的学生的学号：");
  String studentid = input.nextLine();
  System.out.println("请输入新学生的姓名：");
  String newName = input.nextLine();
  System.out.println("请输入新学生的年龄：");
  String newAge = input.nextLine();
  
  //将每一个学生的列出来，for循环判断你要修改信息的学生是哪一个
  NodeList list = doc.getElementsByTagName("student");
  for(int i = 0; i <list.getLength(); i++) {
   if(studentid.equals(list.item(i).getAttributes().getNamedItem("id").getNodeValue())){
    updStudent = (Element) doc.getElementsByTagName("student").item(i).getFirstChild().getParentNode();
    //对学生的name属性进行赋新值
    updStudent.getElementsByTagName("name").item(i).getFirstChild().setNodeValue(newName);
    //对学生的age 属性赋新值
    updStudent.getElementsByTagName("age").item(i).getFirstChild().setNodeValue(newAge);
    
   }else{
    break;
   }
  }
  //找出根元素，将修改后的元素持久化到文件
  Element root = doc.getDocumentElement();
  transform(root);
  System.out.println(updStudent);
 }
 //删除学生信息
 private static void delStudent(Document doc) {
  Scanner input = new Scanner(System.in);
  //输入你要删除的学生的 学号
  System.out.println("请输入要删除学生的学号：");
  String studentid = input.nextLine();
  Element root = doc.getDocumentElement();
  
  //将学生列成一个表，进行遍历，找对应学号的学生进行删除
  NodeList list = doc.getElementsByTagName("student");
  for(int i = 0; i < list.getLength(); i++) {
  if((studentid).equals(list.item(i).getAttributes().getNamedItem("id").getNodeValue())){
   Element delStudent = (Element) doc.getElementsByTagName("student").item(i).getFirstChild().getParentNode(); 
    root.removeChild(delStudent);
    break;
   }else {
    System.out.println("没有该学生");
    break;
   }
  }
  //持久化到文件
  transform(root);
 }
 
 //添加学生信息
 private static void addStudent(Document doc) {
//  System.out.println(doc.getElementsByTagName("student").item(1).getAttributes().getNamedItem("id").getNodeValue());
  Element root = doc.getDocumentElement();
  //从控制台输入
  Scanner input = new Scanner(System.in);
  System.out.println("请输入学生的序号：id = ");
   
  //将学生放到一个列表里面，看我们要添加的学生的学号里面是否已经有了，如果有，需要将新加入的学生的学号改一下
  NodeList list = doc.getElementsByTagName("student");
  String studentid = input.nextLine();
  for(int i = 0; i < list.getLength(); i++) {
   if(studentid.equals(list.item(i).getAttributes().getNamedItem("id").getNodeValue())){
    System.out.println("该序号学生表里面已经存在，请重新输入一个新的序号：");
     studentid = input.nextLine();
   }else {
    break;
   }
  }
  
  System.out.println("请输入要添加学生的姓名：name = ");
  String name_value = input.nextLine();
  System.out.println("请输入要添加学生的年龄：age = ");
  String age_value = input.nextLine();
  
  //创建节点
  Element student = doc.createElement("student");
  Element name = doc.createElement("name");
  Element age = doc.createElement("age");
  Text namText = doc.createTextNode(name_value);
  Text ageText = doc.createTextNode(age_value);
  //关联节点之间的关系
  root.appendChild(student);
  student.appendChild(name);
  student.appendChild(age);
  student.setAttribute("id", studentid);
  name.appendChild(namText);
  age.appendChild(ageText);
  //持久化到文件
  transform(root);
  
 }
 //持久化到文件的方法
 private static void transform(Element root)
   throws TransformerFactoryConfigurationError {
  TransformerFactory factory = TransformerFactory.newInstance();
  try {
   Transformer tf = factory.newTransformer();
   tf.transform(new DOMSource(root), new StreamResult(new File("src/com/briup/dom/student.xml")));
  } catch (TransformerConfigurationException e) {
   e.printStackTrace();
  } catch (TransformerException e) {
   e.printStackTrace();
  }
 }
}

import java.io.File;
import java.io.IOException;
import java.nio.file.attribute.AclEntry.Builder;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.xml.sax.SAXException;

public class Domutils {
 public static Document getDoc(File file) throws SAXException, IOException, ParserConfigurationException {
//获取工厂模式
  DocumentBuilderFactory factory = 
    DocumentBuilderFactory.newInstance();
//获取builder对象
   DocumentBuilder builder = factory.newDocumentBuilder(); 
//将要解析文件加载成一个树状文件，开始解析   
   Document document = builder.parse(file);
  return document;
 }
}