Dom4解析XML文件

XML文件
XML :Extensible Markup Language 可扩展标记语言

XML文档在项目主要用来存配制信息，熟悉XML文档数据编写

解析XML ：在JDK中有API，可以解析，但不方便(读)，在实际应用中，一般用第三方开源组件 （dom4j）

DOM：对HTML文档，基DOM称为HTML DOM ,对XML文档，其DOM称为XML DOM

DOM :Document Object Model 文档对象模型，在我们加载文档到内存中后，会自动构建一个DOM模型（是一个倒立节点树）

在DOM节点树中，主要有三种类型的节点：元素节点、属性节点、文本节点

解析XML文件
Java Bean

package cn.lanqiao.xml;
/**
 * @author 阿木木
 */ //实体类
public class Student {
    private  String sid;
    private  String sname;
    private  String smajor;
    private  String stel;

    public Student(String sid,String sname,String smajor,String stel) {
        this.sid = sid;
        this.sname = sname;
        this.smajor = smajor;
        this.stel = stel;
    }

    public String getSid() {
        return sid;
    }

    public void setSid(String sid) {
        this.sid = sid;
    }

    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

    public String getSmajor() {
        return smajor;
    }

    public void setSmajor(String smajor) {
        this.smajor = smajor;
    }

    public String getStel() {
        return stel;
    }

    public void setStel(String stel) {
        this.stel = stel;
    }

    @Override
    public String toString() {
        return "Student{" +
                "sid='" + sid + '\'' +
                ", sname='" + sname + '\'' +
                ", smajor='" + smajor + '\'' +
                ", stel='" + stel + '\'' +
                '}';
    }
}

xml文件

<?xml version="1.0" encoding="UTF-8"?>
<students> 
  <student sid="2"> 
    <sname>张三</sname>  
    <smajor>软件工程</smajor>  
    <stel>130.......</stel> 
  </student>  
  <student sid="3">
    <sname>李四</sname>
    <smajor>软件工程</smajor>
    <stel>130...</stel>
  </student>
</students>
<!--
  约定大于配制 ： 约束
-->

操作类

package cn.lanqiao.xml;

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

import java.io.FileOutputStream;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * @author 阿木木
 */
public class Dom4JDemo {

    //读取xml文件;
    static final String URL="xmlproject/src/students.xml";
    public static void main(String[] args) throws Exception {
        //添加数据
        //Student student=new Student("3","廖灵妹","软件工程","130...");
        //add(student);
        //获取所有数据
        //List<Student> students = listAll();
        //System.out.println(students);
        //修改数据；
        //stu.setSmajor("dddd");
        //stu.setSname("dddd");
        //stu.setStel("dddd");
        //update(stu);
        // Student stu =get("1");
        //删除数据；
        // delete("1");
    }
    public static  void delete(String sid){
        try{
            SAXReader reader = new SAXReader(); //创建一个流对象;
            //获取根元素;
            Document document = null; //返回一个文档对象 --- 内存中的DOM
            document = reader.read(URL);
            Element root = document.getRootElement();
            List<Element> list = root.elements("student");
            Element findElement = null;
            for(Element e :list){
                if(e.attributeValue("sid").equals(sid)){
                    findElement = e;
                    break;
                }
            }
            if(findElement!=null){
                root.remove(findElement);
            }
            //保存
            OutputFormat format = OutputFormat.createPrettyPrint(); //格式化;
            XMLWriter xmlWriter = new XMLWriter(new FileOutputStream(URL),format);
            xmlWriter.write(document);
            xmlWriter.close();

        }catch (Exception e){e.printStackTrace();}
    }
    public static Student get(String sid){
        Student stu =null;
        try{
            SAXReader reader = new SAXReader(); //创建一个流对象;
            //获取根元素;
            Document document = null; //返回一个文档对象 --- 内存中的DOM
            document = reader.read(URL);
            Element root = document.getRootElement();
            //找到要修改的元素;
            List<Element> list = root.elements("student");
            Element findElement = null;
            for(Element e :list){
                if(e.attributeValue("sid").equals(sid)){
                    findElement = e;
                    break;
                }
            }
            if(findElement!=null){
                stu=new Student(findElement.attributeValue("sid"),findElement.elementText("sname"),findElement.elementText("smajor"),findElement.elementText("stel"));
            }
        }catch (Exception e){e.printStackTrace();}
        return stu;
    }
    public static  void update(Student student){
        try{
            SAXReader reader = new SAXReader(); //创建一个流对象;
            //获取根元素;
            Document document = null; //返回一个文档对象 --- 内存中的DOM
            document = reader.read(URL);
            Element root = document.getRootElement();
            //找到要修改的元素;
            List<Element> list = root.elements("student");
            Element upateElement = null;
            for(Element e :list){
                if(e.attributeValue("sid").equals(student.getSid())){
                    upateElement = e;
                    break;
                }
            }

            //实现修改
            if(upateElement!=null){
                upateElement.element("sname").setText(student.getSname());
                upateElement.element("smajor").setText(student.getSmajor());
                upateElement.element("stel").setText(student.getStel());
            }
            //保存
            OutputFormat format = OutputFormat.createPrettyPrint(); //格式化;
            XMLWriter xmlWriter = new XMLWriter(new FileOutputStream(URL),format);
            xmlWriter.write(document);
            xmlWriter.close();
        }catch (Exception e){e.printStackTrace();}
    }
    public static  void add(Student student){
        try {
            SAXReader reader = new SAXReader(); //创建一个流对象;
            //获取根元素;
            Document document = null; //返回一个文档对象 --- 内存中的DOM
            document = reader.read(URL);
            Element root = document.getRootElement();
            //在根元素的下面添加一个子元素(student);
            Element addStudent = root.addElement("student");
            //设置元素属性;
            addStudent.addAttribute("sid",student.getSid());
            //添加子元素sname,smajor,stel;
            addStudent.addElement("sname").setText(student.getSname());
            addStudent.addElement("smajor").setText(student.getSmajor());
            addStudent.addElement("stel").setText(student.getStel());
            //持久化 --将document对象写入磁盘文件;
            OutputFormat format = OutputFormat.createPrettyPrint(); //格式化;
            XMLWriter xmlWriter = new XMLWriter(new FileOutputStream(URL),format);
            xmlWriter.write(document);
            xmlWriter.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static List<Student> listAll(){
        List<Student> list=new ArrayList<>();
        //加载xml文件 --- 流
        SAXReader reader = new SAXReader(); //创建一个流对象;
        try {
            Document document = reader.read(URL); //返回一个文档对象
            //获取根元素;
            Element root = document.getRootElement();
            //获取根元素下的子元素(student);
            Iterator<Element> it=  root.elementIterator("student");
            Student stu = null;
            while(it.hasNext()){
                Element student = it.next();
                //取属性;
                String sid =student.attributeValue("sid");
                //获取子元素(sname,smajor,stel);
                String sname = student.elementText("sname");
                String smajor = student.elementText("smajor");
                String stel = student.elementText("stel");
                stu = new Student(sid,sname,smajor,stel);
                list.add(stu);
            }
        } catch (DocumentException e) {
            e.printStackTrace();
        }
        return  list;
    }
}

读取
添加
修改
删除

**约束：**能文档语法、格式等加载规则 ----- 需要你遵守 ，XML文档的约束可以使用2种方式：DTD | Schema ,可以为某一个XML文档编写DTD或者Schema,但一般没有必要