JAXP进行DOM和SAX解析

2022-10-22 07:59:50

1.常用XML的解析方式：DOM和SAX

1）DOM思想：将整个XML加载内存中，形成文档对象，所以对XML操作都对内存中文档对象进行。

2）SAX思想：一边解析，一边处理，一边释放内存资源---不允许在内存中保留大规模XML数据

3）DOM和SAX的区别

DOM：支持回写，会将整个XML载入内存，以树形结构方式存储

XML比较复杂的时候，或者当你需要随机处理文档中数据的时候不建议使用

SAX：相比DOM是一种更为轻量级的方案

无法在读取过程中修改XML数据

2.常用解析开发包：JAXP、DOM4J

3.DOM解析原理图

4.使用JAXP进行DOM解析

JAXP:(Java API for XML Processing)开发包是JavaSE的一部分，它由以下几个包及其子包组成：

org.w3c.dom:提供DOM方式解析XML的标准接口

org.xml.sax:提供SAX方式解析XML的标准接口

javax.xml:提供了解析XML文档的类

5.JAXP进行DOM解析的实例（增删改查）

book.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?><书架>

    <书 ISBN="a11" 出版社="清华大学出版社">

        <书名>JavaSE基础</书名>

        <作者>张三</作者>

        <批发价>35.00元</批发价>

        <售价>38.00元</售价>

    </书>

    <书 ISBN="b11" 出版社="北京大学出版社">

        <书名>Android</书名>

        <作者>李四</作者>

        <售价>38.00元</售价>

    </书>

</书架>

JaxpDomDemo.java

package cn.lsl.jaxp;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.transform.Transformer;

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.Node;

import org.w3c.dom.NodeList;

public class JaxpDomDemo {

    public static void main(String[] args) throws Exception {

        //得到解析工厂DocumentBuilderFactory

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

        //得到解析器DocumentBuilder

        DocumentBuilder builder =  factory.newDocumentBuilder();

        //解析指定的XML文档，得到代表内存DOM树的Document对象

        Document document = builder.parse("src/book.xml");

        test8(document);

    }

    //1.得到某个具体节点内容：打印第2本书的作者

    public static void test1(Document document){

        //根据标签的名称获取所有的作者元素

        NodeList nodeList = document.getElementsByTagName("作者");

        //按照索引取第2个作者元素

        Node node = nodeList.item(1);

        //打印该元素的文本

        String text = node.getTextContent();

        System.out.println(text);

    }

    // 2、遍历所有元素节点:打印元素的名称

    public static void test2(Node node){

        //判断当前节点是不是一个元素节点

        if(node.getNodeType() == Node.ELEMENT_NODE){

            //如果是：打印他的名称

            System.out.println(node.getNodeName());

        }

        //查找子节点

        NodeList nodeList = node.getChildNodes();

        int len = nodeList.getLength();

        for (int i = 0; i < len; i++) {

            Node n = nodeList.item(i);

            test2(n);

        }

    }

    //3、修改某个元素节点的主体内容:把第一本书的售价改为38.00元

    public static void test3(Document document) throws Exception{

        //找到第一本书的售价

        NodeList nodeList = document.getElementsByTagName("售价");

        //设置其主体内容

        Node node = nodeList.item(0);

        node.setTextContent("38.00元");

        //把内存中Document树写回xml文件中

        TransformerFactory factory = TransformerFactory.newInstance();

        Transformer ts = factory.newTransformer();

        ts.transform(new DOMSource(document), new StreamResult("src/book.xml"));

    }

    //4.向指定元素节点中增加子元素节点:第一本中增加子元素<内部价>29.00</内部价>

    public static void test4(Document document) throws Exception{

        //创建一个新的元素并设置其主体内容

        Element e = document.createElement("内部价");

        e.setTextContent("29.00元");

        //找到第一本书元素

        Node firstBookNode = document.getElementsByTagName("书").item(0);

        //把新节点挂接到第一本书上

        firstBookNode.appendChild(e);

        //把内存中Document树写回XML文件中

        TransformerFactory factory = TransformerFactory.newInstance();

        Transformer ts = factory.newTransformer();

        ts.transform(new DOMSource(document), new StreamResult("src/book.xml"));

    }

    //5.向指定元素节点上增加同级元素节点:在第一本书的售价前面增加批发价

    public static void test5(Document document) throws Exception{

        //创建一个新的元素并设置其中的主题内容

        Element e = document.createElement("批发价");

        e.setTextContent("35.00元");

        //找到第一本书的售价

        Node firstPrice = document.getElementsByTagName("售价").item(0);

        //在售价的前面加入新建的元素：增加子元素一定要用父元素来增加

        firstPrice.getParentNode().insertBefore(e, firstPrice);

        //把内存中Document树写回XML文件中

        TransformerFactory factory = TransformerFactory.newInstance();

        Transformer ts = factory.newTransformer();

        ts.transform(new DOMSource(document), new StreamResult("src/book.xml"));

    }

    //6.删除指定元素节点：删除内部价

    public static void test6(Document document) throws Exception{

        //找到内部价节点，用父节点删除

        Node n = document.getElementsByTagName("内部价").item(0);

        n.getParentNode().removeChild(n);

        //把内存中Document书写回XML文件中

        TransformerFactory factory = TransformerFactory.newInstance();

        Transformer ts = factory.newTransformer();

        ts.transform(new DOMSource(document), new StreamResult("src/book.xml"));

    }

    //7、操作XML文件属性:打印第一本书的出版社

    public static void test7(Document document){

        //得到第一本书

        Node n = document.getElementsByTagName("书").item(0);

        //打印指定属性的取值

        Element e = (Element)n;

        System.out.println(e.getAttribute("出版社"));

    }

    //8、添加一个出版社属性给第二本书

    public static void test8(Document document) throws Exception{

        //得到第二本书

        Node n = document.getElementsByTagName("书").item(1);

        //打印指定属性的取值

        Element e = (Element)n;

        e.setAttribute("出版社", "北京大学出版社");

        //把内存中Document树写回XML文件中

        TransformerFactory factory  = TransformerFactory.newInstance();

        Transformer ts = factory.newTransformer();

        ts.transform(new DOMSource(document), new StreamResult("src/book.xml"));

    }

}

6.案例（学生成绩的增删改查，采用分层开发）

案例原型

exam.xml

<?xml version="1.0" encoding="UTF-8" standalone="no"?><exam>

    <student examid="444" idcard="333">

        <name>李四</name>

        <location>大连</location>

        <grade>97</grade>

    </student>

    <student examid="666" idcard="555">

        <name>小舒</name>

        <location>福建</location>

        <grade>90.0</grade>

    </student>

</exam>

实体类：Student.java

package cn.lsl.domain;

public class Student {

    private String idcard;

    private String examid;

    private String name;

    private String location;

    private Double 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 Double getGrade() {

        return grade;

    }

    public void setGrade(Double grade) {

        this.grade = grade;

    }

    @Override

    public String toString() {

        return "Student [examid=" + examid + ", grade=" + grade + ", idcard="

                + idcard + ", location=" + location + ", name=" + name + "]";

    }

}

工具类：DocumentUtil.java

package cn.lsl.util;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.transform.Transformer;

import javax.xml.transform.TransformerFactory;

import javax.xml.transform.dom.DOMSource;

import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;

//操作XML的工具类

//工具类中的异常可以抛也可以处理

public class DocumentUtil {

    public static Document getDocument() throws Exception{

        DocumentBuilder builder =  DocumentBuilderFactory.newInstance().newDocumentBuilder();

        return builder.parse("src/exam.xml");

    }

    public static void write2xml(Document document) throws Exception{

        Transformer ts = TransformerFactory.newInstance().newTransformer();

        ts.transform(new DOMSource(document), new StreamResult("src/exam.xml"));

    }

}

DAO层：（StudentDao.java）

package cn.lsl.dao;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

import cn.lsl.domain.Student;

import cn.lsl.util.DocumentUtil;

public class StudentDao {

    //添加学生信息到XML中

    public boolean createStudent(Student s){

        boolean result = false;

        try{

            Document document = DocumentUtil.getDocument();

            //创建name、location、grade元素并设置内容

            Element nameE = document.createElement("name");

            nameE.setTextContent(s.getName());

            Element locationE = document.createElement("location");

            locationE.setTextContent(s.getLocation());

            Element gradeE = document.createElement("grade");

            gradeE.setTextContent(s.getGrade()+"");

            //创建student元素，并设置属性

            Element studentE = document.createElement("student");

            studentE.setAttribute("idcard", s.getIdcard());

            studentE.setAttribute("examid", s.getExamid());

            studentE.appendChild(nameE);

            studentE.appendChild(locationE);

            studentE.appendChild(gradeE);

            //得到exam元素，把student挂接上去

            Node node = document.getElementsByTagName("exam").item(0);

            node.appendChild(studentE);

            //写回XML文件中

            DocumentUtil.write2xml(document);

            result = true;

        }catch(Exception e){

            throw new RuntimeException(e);    //异常转义。异常链

        }

        return result;

    }

    //根据准考证号查询学生信息

    public Student findStudent(String examid){

        Student s = null;

        try{

            Document document = DocumentUtil.getDocument();

            //得到所有student元素

            NodeList nodelist = document.getElementsByTagName("student");

            //遍历student元素，判断他的examid属性的取值是否与参数匹配

            for (int i = 0; i < nodelist.getLength(); i++) {

                Node node = nodelist.item(i);

                if(node instanceof Element){

                    Element e = (Element)node;

                    if(e.getAttribute("examid").equals(examid)){

                        //如果匹配，说明找到了学生，创建学生对象

                        s = new Student();

                        s.setExamid(examid);

                        s.setIdcard(e.getAttribute("idcard"));

                        s.setName(e.getElementsByTagName("name").item(0).getTextContent());

                        s.setLocation(e.getElementsByTagName("location").item(0).getTextContent());

                        s.setGrade(Double.parseDouble(e.getElementsByTagName("grade").item(0).getTextContent()));

                    }

                }

            }

        }catch(Exception e){

            throw new RuntimeException(e);

        }

        return s;

    }

    //根据学生姓名删除学生

    public boolean deleteStudent(String name){

        boolean result = false;

        try{

            //得到Document对象

            Document document = DocumentUtil.getDocument();

            NodeList nodelist = document.getElementsByTagName("name");

            for(int i=0; i<nodelist.getLength(); i++){

                Node node = nodelist.item(i);

                if(node.getTextContent().equals(name)){

                    node.getParentNode().getParentNode().removeChild(node.getParentNode());

                    //写回XML文档

                    DocumentUtil.write2xml(document);

                    result = true;

                    break;

                }

            }

        }catch(Exception e){

                throw new RuntimeException(e);

        }

        return result;

    }

}

View层（Main.java）

package cn.lsl.view;

import java.io.BufferedReader;

import java.io.InputStreamReader;

import cn.lsl.dao.StudentDao;

import cn.lsl.domain.Student;

public class Main {

    public static void main(String[] args) {

        try{

            StudentDao dao = new StudentDao();

            System.out.println("a、添加学生\tb、删除学生\tc、查询成绩");

            System.out.println("请输入操作类型");

            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

            String operation = br.readLine();

            if("a".equals(operation)){

                //添加操作

                System.out.println("请输入学生姓名");

                String name = br.readLine();

                System.out.println("请输入学生准考证号");

                String examid = br.readLine();

                System.out.println("请输入学生身份证号");

                String idcard = br.readLine();

                System.out.println("请输入学生所在地");

                String location = br.readLine();

                System.out.println("请输入学生成绩");

                String grade = br.readLine();

                Student s = new Student();

                s.setExamid(examid);

                s.setIdcard(idcard);

                s.setName(name);

                s.setLocation(location);

                s.setGrade(Double.parseDouble(grade));

                //System.out.println(s);

                boolean b = dao.createStudent(s);

                if(b){

                    System.out.println("---添加成功---");

                }else{

                    System.out.println("对不起！数据有误");

                }

            }else if("b".equals(operation)){

                System.out.println("请输入要删除的学生姓名:");

                String name = br.readLine();

                boolean b = dao.deleteStudent(name);

                if(b){

                    System.out.println("--删除成功--");

                }else{

                    System.out.println("对不起！删除失败或者学生不存在");

                }

            }else if("c".equals(operation)){

                //查询操作

                System.out.println("请输入要查询的学生准考证号:");

                String examid = br.readLine();

                Student s = dao.findStudent(examid);

                if(s == null){

                    System.out.println("对不起！您查询的学生不存在");

                }else{

                    System.out.println(s);

                }

            }else{

                System.out.println("请输入正确的操作类型");

            }

        }catch(Exception e){

            System.out.println("对不起！服务器忙！");

        }

    }

}

7.SAX解析原理图

8. SAX采用事件处理的方式解析XML文件，利用 SAX 解析 XML 文档，涉及两个部分：解析器和事件处理器。

9.SAX解析

实例一：

book.xml

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

<书架>

  <书 出版社="清华大学出版社">

    <书名>JavaSE基础</书名>

    <作者>张三</作者>

    <售价>38.00</售价>

    <内部价>19.00</内部价>

  </书>

  <书>

    <书名>Android</书名>

    <作者>李四</作者>

    <售价>28.00</售价>

  </书>

</书架>

SAXDemo1.java

package cn.lsl.sax;

import javax.xml.parsers.SAXParser;

import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;

import org.xml.sax.ContentHandler;

import org.xml.sax.Locator;

import org.xml.sax.SAXException;

import org.xml.sax.XMLReader;

//JAXP进行SAX解析

public class SAXDemo1 {

    public static void main(String[] args) throws Exception {

        //得到解析工厂SAXParserFactory

        SAXParserFactory factory = SAXParserFactory.newInstance();

        //得到解析器SAXParser

        SAXParser parser = factory.newSAXParser();

        //得到XML读取器：XMLReader

        XMLReader reader = parser.getXMLReader();

        //注册内容处理器：ContentHandler

        reader.setContentHandler(new MyContentHandler());

        //取出XML文档

        reader.parse("src/book.xml");

    }

}

class MyContentHandler implements ContentHandler{

    //解析到文档开始时被调用

    @Override

    public void startDocument() throws SAXException {

        System.out.println("解析到了文档的开始");

    }

    //解析到了元素开始时被调用：    qName元素名称

    @Override

    public void startElement(String uri, String localName, String qName,

            Attributes atts) throws SAXException {

        System.out.println("解析到了元素的开始："+qName);

    }

    //解析到了文本内容被调用

    @Override

    public void characters(char[] ch, int start, int length)

            throws SAXException {

        System.out.println("文本内容："+new String(ch,start,length));

    }

    //解析到元素结束时被调用

    @Override

    public void endElement(String uri, String localName, String qName)

            throws SAXException {

        System.out.println("解析到了元素的结束："+qName);

    }

    //解析到文档结束时被调用

    @Override

    public void endDocument() throws SAXException {

        System.out.println("解析到了文档的结束");

    }

    @Override

    public void endPrefixMapping(String prefix) throws SAXException {

        // TODO Auto-generated method stub

    }

    @Override

    public void ignorableWhitespace(char[] ch, int start, int length)

            throws SAXException {

        // TODO Auto-generated method stub

    }

    @Override

    public void processingInstruction(String target, String data)

            throws SAXException {

        // TODO Auto-generated method stub

    }

    @Override

    public void setDocumentLocator(Locator locator) {

        // TODO Auto-generated method stub

    }

    @Override

    public void skippedEntity(String name) throws SAXException {

        // TODO Auto-generated method stub

    }

    @Override

    public void startPrefixMapping(String prefix, String uri)

            throws SAXException {

        // TODO Auto-generated method stub

    }

}

实例二：

SAXDemo2.java

package cn.lsl.sax;

import javax.xml.parsers.SAXParser;

import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;

import org.xml.sax.ContentHandler;

import org.xml.sax.Locator;

import org.xml.sax.SAXException;

import org.xml.sax.XMLReader;

//打印第2本书的作者

public class SAXDemo2 {

    public static void main(String[] args) throws Exception {

        SAXParser parser = SAXParserFactory.newInstance().newSAXParser();

        XMLReader reader = parser.getXMLReader();

        reader.setContentHandler(new ContentHandler(){    //匿名内部类

            boolean isAuthor = false;    //是不是作者标签

            int index = 0;    //作者标签的索引

            @Override

            public void startElement(String uri, String localName,

                    String qName, Attributes atts) throws SAXException {

                if("作者".equals(qName)){

                    isAuthor = true;

                }

            }

            @Override

            public void characters(char[] ch, int start, int length)

                    throws SAXException {

                if(isAuthor&&index==1){

                    System.out.println(new String(ch,start,length));

                }

            }

            @Override

            public void endElement(String uri, String localName, String qName)

                    throws SAXException {

                if("作者".equals(qName)){

                    index++;

                }

                isAuthor = false;

            }

            @Override

            public void endDocument() throws SAXException {

                // TODO Auto-generated method stub

            }

            @Override

            public void endPrefixMapping(String prefix) throws SAXException {

                // TODO Auto-generated method stub

            }

            @Override

            public void ignorableWhitespace(char[] ch, int start, int length)

                    throws SAXException {

                // TODO Auto-generated method stub

            }

            @Override

            public void processingInstruction(String target, String data)

                    throws SAXException {

                // TODO Auto-generated method stub

            }

            @Override

            public void setDocumentLocator(Locator locator) {

                // TODO Auto-generated method stub

            }

            @Override

            public void skippedEntity(String name) throws SAXException {

                // TODO Auto-generated method stub

            }

            @Override

            public void startDocument() throws SAXException {

                // TODO Auto-generated method stub

            }

            @Override

            public void startPrefixMapping(String prefix, String uri)

                    throws SAXException {

                // TODO Auto-generated method stub

            }

        });

        reader.parse("src/book.xml");

    }

}

实例三：读取XML内容，封装到JavaBean

Book.java

package cn.lsl.domain;

public class Book {

    private String name;

    private String author;

    private Double price;

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public String getAuthor() {

        return author;

    }

    public void setAuthor(String author) {

        this.author = author;

    }

    public Double getPrice() {

        return price;

    }

    public void setPrice(Double price) {

        this.price = price;

    }

    @Override

    public String toString() {

        return "Book [author=" + author + ", name=" + name + ", price=" + price

                + "]";

    }

}

SAXDemo3.java

package cn.lsl.sax;

import java.util.ArrayList;

import java.util.List;

import javax.xml.parsers.SAXParser;

import javax.xml.parsers.SAXParserFactory;

import org.xml.sax.Attributes;

import org.xml.sax.SAXException;

import org.xml.sax.XMLReader;

import org.xml.sax.helpers.DefaultHandler;

import cn.lsl.domain.Book;

//读取XML内容，封装到JavaBean

public class SAXDemo3 {

    public static void main(String[] args) throws Exception {

        SAXParser parser = SAXParserFactory.newInstance().newSAXParser();

        XMLReader reader =  parser.getXMLReader();

        final List books = new ArrayList();

        reader.setContentHandler(new DefaultHandler(){

            Book book = null;

            String currentTagName = null;

            @Override

            public void startElement(String uri, String localName,

                    String qName, Attributes attributes) throws SAXException {

                if("书".equals(qName)){

                    book = new Book();

                }

                currentTagName = qName;

            }

            @Override

            public void characters(char[] ch, int start, int length)

                    throws SAXException {

                if("书名".equals(currentTagName)){

                    book.setName(new String(ch,start,length));

                }

                if("作者".equals(currentTagName)){

                    book.setAuthor(new String(ch,start,length));

                }

                if("售价".equals(currentTagName)){

                    book.setPrice(Double.parseDouble(new String(ch,start,length)));

                }

            }

            @Override

            public void endElement(String uri, String localName, String qName)

                    throws SAXException {

                if("书".equals(qName)){

                    books.add(book);

                    book = null;

                }

                currentTagName = null;

            }

        });

        reader.parse("src/book.xml");

        for (Object b:books) {

            System.out.println(b);

        }

    }

}

码农公寓

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