Java——DOM解析XML

迈不过友情╰ 2022-06-06 14:07 293阅读 0赞

关于XML：[基础知识][Link 1]  
关于DTD：[基础知识][Link 2]  
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xml
    public 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>

[Link 1]: http://www.w3school.com.cn/xmldom/
[Link 2]: http://www.w3school.com.cn/dtd/