JAXP开发工具包j2se的一部分，它由javax.xml、org.w3c.dom、org.xml.sax 包及其子包组成。

在javax.xml.parsers包中，定义了几个工厂类，通过调用这几个工厂类，可以创建dom和sax解析器，对XML文档进行解析。

自己尝试使用了DOM解析器来解析XML文档，给大家分享下经验，第一次写技术BLOG，有缺陷的地方还望大家拍砖。

具体代码和注释如下：

1、创建一个XmlUtils类，这里面写2个方法，一个方法是用来得到Document对象，一个方法用来将内存中的数据写入指定XML文档。

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.TransformerConfigurationException;
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.xml.sax.SAXException;


public class XmlUtils {
//定义文档路径
public static String filename = "src/test.xml";
//获取解析后的XML文档方法
public static Document getDocument() throws Exception {
//获取Dom工厂实例
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
//获取Dom解析器
DocumentBuilder builder = factory.newDocumentBuilder();
//解析所需文档
return builder.parse(filename);
}
//将内存中的数据写入XML中
    public static void document2Xml(Document document) throws Exception{
    //获取工厂实例
    TransformerFactory tffactory=TransformerFactory.newInstance();
    //获取Transformer对象
    Transformer tf =tffactory.newTransformer();
    //调用transform(Source xmlSource,Result outputTarget) 方法，将内存数据写入指定XML
    tf.transform(new DOMSource(document),new StreamResult(new FileOutputStream(filename)));
    }    
}

2、用XML作为数据库存储学生的信息（姓名，城市和身份证号），创建一个StudentBean类，来获取Student对象

public class StudentBean {
private String name;
private double idcard;
private String city;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getIdcard() {
return idcard;
}
public void setIdcard(double idcard) {
this.idcard = idcard;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
}

3、StudentDao类来处理对XML增删查的功能

import java.io.IOException;
import javax.xml.parsers.ParserConfigurationException;
import org.junit.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
import cn.shenyoujun.Bean.StudentBean;
import cn.shenyoujun.Exception.StudentNotExistException;
import cn.shenyoujun.XmlUtils.XmlUtils;


public class StudentDao {
//增加学生信息方法
public void add(StudentBean student) {
try {
Document document = XmlUtils.getDocument();
Element student_tag = document.createElement("student");
student_tag.setAttribute("name",student.getName());
Element idcard = document.createElement("idcard");
Element city = document.createElement("city");
idcard.setTextContent(student.getIdcard() + "");
city.setTextContent(student.getCity());
student_tag.appendChild(idcard);
student_tag.appendChild(city);
document.getElementsByTagName("exam").item(0)
.appendChild(student_tag);
XmlUtils.document2Xml(document);
System.out.print("添加成功");
} catch (Exception e) {
// TODO Auto-generated catch block
throw new RuntimeException(e);
}
}

//删除学生信息方法
public void remove(String name) throws StudentNotExistException {


try {
Document document = XmlUtils.getDocument();
NodeList list = document.getElementsByTagName("student");
StudentBean sb = new StudentBean();
for (int i = 0; i < list.getLength(); i++) {
Element student = (Element) list.item(i);
if (student.getAttribute("name").equals(name)) {
list.item(i).getParentNode().removeChild(list.item(i));
XmlUtils.document2Xml(document);
}
}
throw new StudentNotExistException(name + "不存在！");
} catch (StudentNotExistException e) {
throw e;
} catch (Exception e) {
throw new RuntimeException(e);
}
}
//寻找学生信息方法
public StudentBean search(String name) {
try {
Document document = XmlUtils.getDocument();
NodeList list = document.getElementsByTagName("student");
StudentBean sb = new StudentBean();
for (int i = 0; i < list.getLength(); i++) {
Element student = (Element) list.item(i);
if (student.getAttribute("name").equals(name)) {
sb.setName(name);
sb.setIdcard(Double.parseDouble(student
.getElementsByTagName("idcard").item(0)
.getTextContent()));
sb.setCity(student.getElementsByTagName("city").item(0)
.getTextContent());
return sb;
}
}
return null;
} catch (Exception e) {
// TODO Auto-generated catch block
throw new RuntimeException(e);
}
}
}

4、最后写个单元测试类，来测试这些功能

package Junit;
import org.junit.Test;
import cn.shenyoujun.Bean.StudentBean;
import cn.shenyoujun.Dao.StudentDao;
import cn.shenyoujun.Exception.StudentNotExistException;

public class TestStudentDao {
@Test
public void testAdd() {
StudentDao sd = new StudentDao();
StudentBean s = new StudentBean();
s.setName("张三");
s.setCity("nanjing");
s.setIdcard(2);
sd.add(s);
} 
@Test
public void testSearch(){
StudentDao sd = new StudentDao();
String name="张三";
StudentBean sb=sd.search(name);
System.out.print(sb.getName()+"  "+sb.getCity()+"  "+sb.getIdcard());
}
@Test
public void testRemove(){
StudentDao sd = new StudentDao();
String name="张三";
try {
sd.remove(name);
} catch (StudentNotExistException e) {
e.printStackTrace();
}
}
}

总结下Dom解析的优劣点：

使用Dom解析的原理是将所有的标签和熟悉都解析成对象存入到内存中，优点是对做增删改的操作比较方便

但是缺点是对内存消耗大，不宜做查询。