Java——DOM解析XML

关于XML：基础知识
关于DTD：基础知识
常用的两种XML解析技术：

• DOM：将整个xml文件读入内存并将xml中的标签生成一棵对象树，程序对于xml标签的操作转换为对树结构的操作，优点是增删改查比较方便，缺点是占用内存大，不适合大文档；
• SAX：边解析边处理，占用内存少，解析速度快，但是只能读取XML文件不能进行增删改操作。
  常用的几个操作：

package com.kexin.day2;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import javax.xml.parsers.ParserConfigurationException;import javax.xml.transform.Transformer;import javax.xml.transform.TransformerException;import javax.xml.transform.TransformerFactory;import javax.xml.transform.dom.DOMSource;import javax.xml.transform.stream.StreamResult;import org.junit.After;import org.junit.Before;import org.junit.Test;import org.w3c.dom.Document;import org.w3c.dom.Element;import org.w3c.dom.Node;import org.w3c.dom.NodeList;import org.xml.sax.SAXException;//使用J2SE自带的xml解析器解析xmlpublic class Demo1 {    Document document;    @Before    public void Before() throws ParserConfigurationException, SAXException, IOException {        // 获取xml文件生成的对象树        DocumentBuilderFactory builderfactory = DocumentBuilderFactory.newInstance();        DocumentBuilder db = builderfactory.newDocumentBuilder();        document = db.parse("src/com/kexin/day2/PRODUCT.xml");    }    // 递归遍历对象树(空格回车也是一个节点）    public static void list(Node n) {        NodeList nl = n.getChildNodes();        System.out.println(n.getNodeName());        for (int i = 0; i < nl.getLength(); i++) {            Node node = nl.item(i);            list(node);        }    }    @Test    public void test() {        list(document);    }    // 获取结点属性值    @Test    public void test1() {        NodeList nl = document.getElementsByTagName("PRODUCT");        for (int i = 0; i < nl.getLength(); i++) {            Node node = nl.item(i);            Element e = (Element) node;            System.out.println(e.getAttribute("name"));        }    }    // 向xml文件中增加新节点    @Test    public void test2() throws FileNotFoundException, TransformerException {        Element e = document.createElement("PRODUCT");        e.setAttribute("name", "ipad");        Element e1 = document.createElement("PRODUCE");        e1.setTextContent("apple");        Element e2 = document.createElement("PRICE");        e2.setTextContent("1800");        // 将结点添加到对象树，还有insertBefore等方法        Node node = document.getElementsByTagName("PRODUCTS").item(0);        e.appendChild(e1);        e.appendChild(e2);        node.appendChild(e);    }    // 更改或添加xml属性节点的值    @Test    public void test3() {        Element e = (Element) document.getElementsByTagName("PRODUCT").item(0);        e.setAttribute("name", "phone");    }    //删除xml中的节点    @Test    public void test4(){        Node node = document.getElementsByTagName("PRODUCT").item(0);        node.getParentNode().removeChild(node);    }    @After    public void after() throws FileNotFoundException, TransformerException {        // 将document写入xml        TransformerFactory tff = TransformerFactory.newInstance();        Transformer tf = tff.newTransformer();        tf.transform(new DOMSource(document), new StreamResult(new FileOutputStream("src/com/kexin/day2/PRODUCT.xml")));    }}

PRODUCT.xml：

<?xml version="1.0" encoding="UTF-8" standalone="no"?><PRODUCTS><PRODUCT name="手机">    <PRODUCE>华为</PRODUCE>    <PRICE>2000</PRICE></PRODUCT><PRODUCT name="ipad">    <PRODUCE>apple</PRODUCE>    <PRICE>2400</PRICE></PRODUCT><PRODUCT name="电脑">    <PRODUCE>华硕</PRODUCE>    <PRICE>4200</PRICE></PRODUCT></PRODUCTS>

作业：使用DOM实现对XML文件的一系列操作，模拟数据库存取改，实现学生信息录入、删除、读取

package com.kexin.day2;import java.io.File;import java.io.IOException;import java.util.Scanner;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import javax.xml.parsers.ParserConfigurationException;import javax.xml.transform.Transformer;import javax.xml.transform.TransformerException;import javax.xml.transform.TransformerFactory;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.xml.sax.SAXException;public class StuTask {    private final String xml_path = "src/com/kexin/day2/stu_info.xml";    private final String STU = "stu", EXAM = "exam", EXAMID = "examid", IDCARD = "idcard", NAME = "name",            LOCATION = "location", GRADE = "grade";    /*     * 添加新用户     */    public void AddStu() throws ParserConfigurationException, SAXException, IOException, TransformerException {        Student stu = new Student();        Scanner s1 = new Scanner(System.in);        System.out.println("请输入学生姓名");        stu.setName(s1.nextLine());        System.out.println("请输入准考证号");        stu.setExamid(s1.nextLine());        System.out.println("请输入身份证号");        stu.setIdcard(s1.nextLine());        System.out.println("请输入学生地址");        stu.setLocation(s1.nextLine());        System.out.println("请输入学生成绩");        stu.setGrade(s1.nextLine());        Document document = this.GetDocument(xml_path);        // 创建stu标签        Element stu_node = document.createElement(STU);        stu_node.setAttribute(IDCARD, stu.getIdcard());        stu_node.setAttribute(EXAMID, stu.getExamid());        // 创建stu标签内的name location grade标签        Element stu_name_node = document.createElement(NAME);        stu_name_node.setTextContent(stu.getName());        Element stu_location_node = document.createElement(LOCATION);        stu_location_node.setTextContent(stu.getLocation());        Element stu_grade_node = document.createElement(GRADE);        stu_grade_node.setTextContent(stu.getGrade());        // 将子标签添加到stu标签内        stu_node.appendChild(stu_name_node);        stu_node.appendChild(stu_location_node);        stu_node.appendChild(stu_grade_node);        document.getElementsByTagName(EXAM).item(0).appendChild(stu_node);        this.SvaeToXML(document);    }    /*     * 删除用户     */    public void DeleteStu() throws ParserConfigurationException, SAXException, IOException, TransformerException {        System.out.println("请输入准考证号");        Scanner s1 = new Scanner(System.in);        String examid = s1.nextLine();        Document document = this.GetDocument(xml_path);        NodeList nl = document.getElementsByTagName(STU);        Element e;        for(int i = 0;i<nl.getLength();i++){            e = (Element) nl.item(i);            if(e.getAttribute(EXAMID).equals(examid)){                nl.item(i).getParentNode().removeChild(nl.item(i));                break;            }        }        this.SvaeToXML(document);    }    /*     * 查询成绩     */    public void QuestStu() throws ParserConfigurationException, SAXException, IOException {        System.out.println("请输入准考证号");        Scanner s1 = new Scanner(System.in);        String examid = s1.nextLine();        Document document = this.GetDocument(xml_path);        NodeList nl = document.getElementsByTagName(STU);        Element e;        for(int i = 0;i<nl.getLength();i++){            e = (Element) nl.item(i);            if(e.getAttribute(EXAMID).equals(examid)){                System.out.println(e.getElementsByTagName(GRADE).item(0).getTextContent());                break;            }        }    }    public Document GetDocument(String path) throws ParserConfigurationException, SAXException, IOException {        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();        DocumentBuilder db = dbf.newDocumentBuilder();        Document document = db.parse(path);        return document;    }    public static void main(String[] args)            throws ParserConfigurationException, SAXException, IOException, TransformerException {        int key = 0;        StuTask st = new StuTask();        Scanner scan = new Scanner(System.in);        System.out.println("请选择操作：");        while (key != 4) {            System.out.println("1、添加新用户；2、删除用户；3、查询成绩；4、退出系统");            key = scan.nextInt();            switch (key) {            case 1:                st.AddStu();                break;            case 2:                st.DeleteStu();                break;            case 3:                st.QuestStu();                break;            default:                key = 4;            }        }    }    /*     * 将document输出至xml文件     */    public void SvaeToXML(Document document) throws TransformerException {        TransformerFactory tff = TransformerFactory.newInstance();        Transformer tf = tff.newTransformer();        tf.transform(new DOMSource(document), new StreamResult(new File(xml_path)));    }}

Student类：

package com.kexin.day2;public class Student {    private String idcard;    private String examid;    private String name;    private String location;    private String 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 String getGrade() {        return grade;    }    public void setGrade(String grade) {        this.grade = grade;    }}

stu_info.xml：

<?xml version="1.0" encoding="UTF-8" standalone="no"?><exam>    <stu examid="222" idcard="111">        <name>张三</name>        <location>济南</location>        <grade>99</grade>    </stu>    <stu examid="142" idcard="325">        <name>李四</name>        <location>青岛</location>        <grade>88</grade>    </stu></exam>