Java&Xml教學（二）使用DOM方式解析XML文件-XML/RSS教程-PHP中文網

DOM XML 解析方式是最容易理解的，它將XML文件作为Document对象读取到内存中，然后你可以轻松地遍历不同的元素和节点对象。遍历元素和节点不需要按照顺序进行。
DOM解析方式适合尺寸较小的XML文件，由于它將整个XML文件全部装载到内存中处理，所以不太适合处理尺寸较大的XML文件。对于较大的XML文件需要使用SAX解析。
在本教程中我们将对XML文件读取和解析，并用它来创建对象。下面是我们将要解析的XML文件。
employee.xml

<?xml version="1.0"?><Employees>
    <Employee>
        <name>Pankaj</name>
        <age>29</age>
        <role>Java Developer</role>
        <gender>Male</gender>
    </Employee>
    <Employee>
        <name>Lisa</name>
        <age>35</age>
        <role>CSS Developer</role>
        <gender>Female</gender>
    </Employee></Employees>

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这个XML文件的内容是一些员工信息列表，因此我们需要创建一个Employee类来表示员工，然后將XML文件信息读取到程序中。
下面是Employee类的定义：

package com.journaldev.xml;public class Employee {
    private String name;    
    private String gender;    
    private int age;    
    private String role;    
    public String getName() {        
    return name;
    }    public void setName(String name) {        this.name = name;
    }    public String getGender() {        return gender;
    }    public void setGender(String gender) {        this.gender = gender;
    }    public int getAge() {        return age;
    }    public void setAge(int age) {        this.age = age;
    }    public String getRole() {        return role;
    }    public void setRole(String role) {        this.role = role;
    }    @Override
    public String toString() {        
    return "Employee:: Name=" + this.name + " Age=" + this.age + " Gender=" + this.gender +                
    " Role=" + this.role;
    }

}

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需要注意的是这里我重写了toString()方法以便打印出员工对象的有用信息。接下来我们在程序中使用DOM解析方式读取XML文件来获取Employee 对象列表。
XMLReaderDOM.java

package com.journaldev.xml;
import java.io.File;import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
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;public class XMLReaderDOM {

    public static void main(String[] args) {
        String filePath = "employee.xml";
        File xmlFile = new File(filePath);
        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder;
        try {
            dBuilder = dbFactory.newDocumentBuilder();
            Document doc = dBuilder.parse(xmlFile);
            doc.getDocumentElement().normalize();
            System.out.println("Root element :" + doc.getDocumentElement().getNodeName());
            NodeList nodeList = doc.getElementsByTagName("Employee");
            //now XML is loaded as Document in memory, lets convert it to Object List
            List<Employee> empList = new ArrayList<Employee>();
            for (int i = 0; i < nodeList.getLength(); i++) {
                empList.add(getEmployee(nodeList.item(i)));
            }
            //lets print Employee list information
            for (Employee emp : empList) {
                System.out.println(emp.toString());
            }
        } catch (SAXException | ParserConfigurationException | IOException e1) {
            e1.printStackTrace();
        }

    }


    private static Employee getEmployee(Node node) {
        //XMLReaderDOM domReader = new XMLReaderDOM();
        Employee emp = new Employee();
        if (node.getNodeType() == Node.ELEMENT_NODE) {
            Element element = (Element) node;
            emp.setName(getTagValue("name", element));
            emp.setAge(Integer.parseInt(getTagValue("age", element)));
            emp.setGender(getTagValue("gender", element));
            emp.setRole(getTagValue("role", element));
        }

        return emp;
    }


    private static String getTagValue(String tag, Element element) {
        NodeList nodeList = element.getElementsByTagName(tag).item(0).getChildNodes();
        Node node = (Node) nodeList.item(0);
        return node.getNodeValue();
    }

}

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程序输出内容如下：

Root element :EmployeesEmployee:: Name=Pankaj Age=29 Gender=Male 
Role=Java DeveloperEmployee:: Name=Lisa Age=35 Gender=Female Role=CSS Developer

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在实际情况下，我们在解析XML文件之前先要对XML文件的合法性进行校验，学习如何使用XSD校验XML文件。

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<?xml version="1.0"?><Employees>
    <Employee>
        <name>Pankaj</name>
        <age>29</age>
        <role>Java Developer</role>
        <gender>Male</gender>
    </Employee>
    <Employee>
        <name>Lisa</name>
        <age>35</age>
        <role>CSS Developer</role>
        <gender>Female</gender>
    </Employee></Employees>

登入後複製

这个XML文件的内容是一些员工信息列表，因此我们需要创建一个Employee类来表示员工，然后將XML文件信息读取到程序中。
下面是Employee类的定义：

package com.journaldev.xml;public class Employee {
    private String name;    
    private String gender;    
    private int age;    
    private String role;    
    public String getName() {        
    return name;
    }    public void setName(String name) {        
    this.name = name;
    }    public String getGender() {        
    return gender;
    }    public void setGender(String gender) {        
    this.gender = gender;
    }    public int getAge() {        
    return age;
    }    public void setAge(int age) {        
    this.age = age;
    }    public String getRole() {        
    return role;
    }    public void setRole(String role) {        
    this.role = role;
    }    @Override
    public String toString() {        
    return "Employee:: Name=" + this.name + " Age=" + this.age + " Gender=" + this.gender +                
    " Role=" + this.role;
    }

}

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package com.journaldev.xml;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
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;public class XMLReaderDOM {

    public static void main(String[] args) {
        String filePath = "employee.xml";
        File xmlFile = new File(filePath);
        DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder dBuilder;
        try {
            dBuilder = dbFactory.newDocumentBuilder();
            Document doc = dBuilder.parse(xmlFile);
            doc.getDocumentElement().normalize();
            System.out.println("Root element :" + doc.getDocumentElement().getNodeName());
            NodeList nodeList = doc.getElementsByTagName("Employee");
            //now XML is loaded as Document in memory, lets convert it to Object List
            List<Employee> empList = new ArrayList<Employee>();
            for (int i = 0; i < nodeList.getLength(); i++) {
                empList.add(getEmployee(nodeList.item(i)));
            }
            //lets print Employee list information
            for (Employee emp : empList) {
                System.out.println(emp.toString());
            }
        } catch (SAXException | ParserConfigurationException | IOException e1) {
            e1.printStackTrace();
        }

    }


    private static Employee getEmployee(Node node) {
        //XMLReaderDOM domReader = new XMLReaderDOM();
        Employee emp = new Employee();
        if (node.getNodeType() == Node.ELEMENT_NODE) {
            Element element = (Element) node;
            emp.setName(getTagValue("name", element));
            emp.setAge(Integer.parseInt(getTagValue("age", element)));
            emp.setGender(getTagValue("gender", element));
            emp.setRole(getTagValue("role", element));
        }

        return emp;
    }


    private static String getTagValue(String tag, Element element) {
        NodeList nodeList = element.getElementsByTagName(tag).item(0).getChildNodes();
        Node node = (Node) nodeList.item(0);
        return node.getNodeValue();
    }

}

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程序输出内容如下：

Root element :EmployeesEmployee:: Name=Pankaj Age=29 Gender=Male Role=Java DeveloperEmployee:: Name=Lisa Age=35 Gender=Female Role=CSS Developer

登入後複製

在实际情况下，我们在解析XML文件之前先要对XML文件的合法性进行校验，学习如何使用XSD校验XML文件。

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