XML 解析

　　XML解析的分式分为两种，DOM和SAX。
　　DOM（Document Object Model，即文挡对象模型）是W3C组织推荐的解析XML的一种方式。DOM解析的缺点是文挡太大的话，内存消耗大，速度慢。但对DOM进行增删查改很方便。
　　SAX是一个用于处理XML事件驱动的“推”模型，虽然它不是W3C标准，但它却是一个得到了广泛认可的API。SAX解析器不像DOM那样建立一个完整的文档树，而是在读取文档时激活一系列事件，这些事件被推给事件处理器，然后由事件处理器提供对文档内容的访问。SAX不会产生内存消耗大，但不能对数据进行增删改，只能对数据进行数据的读取。

　　XML解析开发包：JAXP(SUN)，DOM4J
　　

　　JAXP开发包是J2SE的一部份，它由JAVA.XML、ORG.W3C.DOM、ORG.XML.SAX包及其子包组成。在JAVA.XML.PARSERS包中，定义了几个工厂类，程序员调用这些工厂类，可以得到XML文挡的DOM或SAX的解析器，从而实现对XML文挡的解析。在JAVA.XML.PARSERS包中DocumentBuilderFactory用于创建DOM模式的解析器对象，DocumentBuilderFactory是一个抽象工厂类，不能直接实例好。该类提供了一个newInstance方法用于创建一个工厂对象。

　　使用JAXP创建一个XML解析文挡

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;

public class demo1 {
    public static void main(String[] args) throws Exception {
        //创建工厂
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        //得到DOM解析器
        DocumentBuilder builder = factory.newDocumentBuilder();
        //解析XML文挡
        Document document =    builder.parse("src/book.xml");
        
    
    }
}

　　使用JAXP对XML进行查操作

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;


public class demo1 {
    public static void main(String[] args) throws Exception {
        // 创建工厂
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        // 得到DOM解析器
        DocumentBuilder builder = factory.newDocumentBuilder();
        // 解析XML文挡
        Document document = builder.parse("src/book.xml");

    }

    @Test
    public void read() throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();

        Document document = builder.parse("src/book.xml");
        NodeList list = document.getElementsByTagName("书名");
        Node node = list.item(0);
        String content = node.getTextContent();
        System.out.println(content);
    }

    //递归的例子
    @Test
    public void read2() throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document document = builder.parse("src/book.xml");

        // 得到根结点
        Node root = document.getElementsByTagName("书架").item(0);
        list(root);
    }

    private void list(Node node) {
        if(node instanceof org.w3c.dom.Element){
            System.out.println(node.getNodeName());
        }
        NodeList list = node.getChildNodes();
        for(int i=0;i<list.getLength();i++){
            Node child = list.item(i);
            list(child);
        }
    }
    
    //得到XML文档中的标签属性
    @Test
    public void read3() throws Exception{
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse("src/book.xml");
        
        Element node = (Element)dom.getElementsByTagName("书架").item(0);
        String value = node.getAttribute("电话");
        System.out.println(value);
    }
    
}

　　使用JAXP对XML文挡进行增删改

import java.io.FileOutputStream;

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.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class demo1 {

    @Test
    public void add() throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse("src/book.xml");
        
        //创建节点
        Element price = dom.createElement("价格");
        price.setTextContent("100");
    
        //把节点加到第一本书上
        Element book =  (Element)dom.getElementsByTagName("书").item(0);
        book.appendChild(price);
        
        //把更新后的内容从内存中写回XML文挡里
        TransformerFactory tffactory = TransformerFactory.newInstance();
        Transformer tf = tffactory.newTransformer();
        tf.transform(new DOMSource(dom), new StreamResult(new FileOutputStream("src/book.xml")));
    
    }
    
    //往指定的位置前插入节点
    @Test
    public void add2() throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse("src/book.xml");
        
        //创建节点
        Element price = dom.createElement("价格");
        price.setTextContent("100");
    
        //得到参考节点
        Element refNode = (Element)dom.getElementsByTagName("作者").item(0);
        
        //往指定的位置前插入节点
        Element book = (Element)dom.getElementsByTagName("书").item(0);
        book.insertBefore(price, refNode);
        
        
        //把更新后的内容从内存中写回XML文挡里
        TransformerFactory tffactory = TransformerFactory.newInstance();
        Transformer tf = tffactory.newTransformer();
        tf.transform(new DOMSource(dom), new StreamResult(new FileOutputStream("src/book.xml")));
    
    }
    
    //往XML结点上添加属性
    @Test
    public void addAttr() throws Exception{
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse("src/book.xml");
        
        //添加属性
        Element bookName = (Element)dom.getElementsByTagName("书名").item(0);
        bookName.setAttribute("name", "xxxx");
    
        //把更新后的内容从内存中写回XML文挡里
        TransformerFactory tffactory = TransformerFactory.newInstance();
        Transformer tf = tffactory.newTransformer();
        tf.transform(new DOMSource(dom), new StreamResult(new FileOutputStream("src/book.xml")));
    }
    
    //删除
    @Test
    public void delete() throws Exception{
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse("src/book.xml");
        
        //得到要删除的结点
        Element e = (Element)dom.getElementsByTagName("价格").item(0);
        //得到要删除结点的爸爸
        Element book = (Element)dom.getElementsByTagName("书").item(0);
        //爸爸删除儿子
        book.removeChild(e);
        
        //把更新后的内容从内存中写回XML文挡里
        TransformerFactory tffactory = TransformerFactory.newInstance();
        Transformer tf = tffactory.newTransformer();
        tf.transform(new DOMSource(dom), new StreamResult(new FileOutputStream("src/book.xml")));
    }
    
    //删除2
    @Test
    public void delete2() throws Exception{
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse("src/book.xml");
        
        //得到要删除的结点
        Element e = (Element)dom.getElementsByTagName("价格").item(0);
        e.getParentNode().removeChild(e);
        
        //把更新后的内容从内存中写回XML文挡里
        TransformerFactory tffactory = TransformerFactory.newInstance();
        Transformer tf = tffactory.newTransformer();
        tf.transform(new DOMSource(dom), new StreamResult(new FileOutputStream("src/book.xml")));
    }
    
    //更新价格
    @Test
    public void update() throws Exception{
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse("src/book.xml");
    
        Element e = (Element)dom.getElementsByTagName("价格").item(0);
        e.setTextContent("100");
        
        //把更新后的内容从内存中写回XML文挡里
        TransformerFactory tffactory = TransformerFactory.newInstance();
        Transformer tf = tffactory.newTransformer();
        tf.transform(new DOMSource(dom), new StreamResult(new FileOutputStream("src/book.xml")));
    
    }
    
}

BOOK.XML

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<书架 电话="89891231">
 <书>
  <书名 name="xxxx">C#程序设计</书名>
  <作者>Ketty</作者>
  <价格>100</价格>
 </书>
 <书>
  <书名>Java程序设计</书名>
  <作者>Okla</作者>
  <价格>77</价格>
 </书>
</书架>

 ================================

一个踪合的例子

//EXAM.XML文件
//---------------------------------------------------------------
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<exam>
    <student examid="222" idcard="111">
        <name>张三</name>
        <location>汕头</location>
        <grade>89</grade>
    </student>
    <student examid="444" idcard="333">
        <name>李四</name>
        <location>广州</location>
        <grade>67</grade>
    </student>
    <student examid="121">
        <name>aaa</name>
        <location>北京</location>
        <grade>89</grade>
    </student>
</exam>


//---------------------------------------------------------------
//XMLUTILS文件
//---------------------------------------------------------------
import java.io.FileOutputStream;
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;

public class XmlUtils {
    private static String fileName = "src/exam.xml";

    public static Document getDocument() throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document dom = builder.parse(fileName);
        return dom;
    }

    public static void writeXml(Document dom) throws Exception {
        // 把更新后的内容从内存中写回XML文挡里
        TransformerFactory tffactory = TransformerFactory.newInstance();
        Transformer tf = tffactory.newTransformer();
        tf.transform(new DOMSource(dom), new StreamResult(new FileOutputStream(
                fileName)));
    }
}


//---------------------------------------------------------------
//Student.DAO文件
//---------------------------------------------------------------
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

public class StudentDao {

    //增加
    public void add(Student s) {
        try {
            Document dom = XmlUtils.getDocument();
            // 创建出封装学生信息的标签
            Element student_tag = dom.createElement("student");
            student_tag.setAttribute("examid", s.getIdcard());
            student_tag.setAttribute("examid", s.getExamid());

            // 创建用于封装学生姓名，所在地和成绩的标签
            Element name = dom.createElement("name");
            Element location = dom.createElement("location");
            Element grade = dom.createElement("grade");

            name.setTextContent(s.getName());
            location.setTextContent(s.getLocation());
            grade.setTextContent(s.getGrade());

            student_tag.appendChild(name);
            student_tag.appendChild(location);
            student_tag.appendChild(grade);

            dom.getElementsByTagName("exam").item(0).appendChild(student_tag);
            // 将结果保存
            XmlUtils.writeXml(dom);
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    //查找
    public Student find(String examid) {

        try {
            Document dom = XmlUtils.getDocument();
            NodeList list = dom.getElementsByTagName("student");
            for (int i = 0; i < list.getLength(); i++) {
                Element student_tag = (Element) list.item(i);
                if (student_tag.getAttribute("examid") == examid) {
                    Student s = new Student();
                    s.setExamid(examid);
                    s.setIdcard(student_tag.getAttribute("idcard"));
                    s.setName(student_tag.getElementsByTagName("name").item(0)
                            .getTextContent());
                    s.setLocation(student_tag.getElementsByTagName("location")
                            .item(0).getTextContent());
                    s.setGrade(student_tag.getElementsByTagName("grade")
                            .item(0).getTextContent());
                    return s;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
    
    //删除
    public boolean delete(String name){
        try {
            Document dom = XmlUtils.getDocument();
            NodeList list = dom.getElementsByTagName("name");
            for(int i=0;i<list.getLength();i++){
                if(list.item(i).getTextContent() == name){
                    //寻找爸爸删除儿子
                    list.item(i).getParentNode().getParentNode().removeChild(list.item(i).getParentNode());
                    XmlUtils.writeXml(dom);
                    return true;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
        
    }

}


//---------------------------------------------------------------
//Student文件
//---------------------------------------------------------------
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;
    }
    
}



//---------------------------------------------------------------
//TestDemo文件
//---------------------------------------------------------------
import org.junit.Test;

public class DemoTest {
    public static void main(String[] args) {

    }

    @Test
    public void testAdd() {
        StudentDao dao = new StudentDao();
        Student s = new Student();
        s.setExamid("121");
        s.setGrade("89");
        s.setIdcard("121");
        s.setLocation("北京");
        s.setName("aaa");
        dao.add(s);
    }

    @Test
    public void testFind() {
        StudentDao dao = new StudentDao();
        Student s = new Student();
        s = dao.find("444");
        System.out.println(s.getName());
    }
}