JAXP进行DOM和SAX解析

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);
        }
    }
}