Java&Xml Tutorial (2) Using DOM to parse XML files

DOM XML parsing method is the easiest to understand. It reads the XML file into memory as a Document object, and then you can easily traverse different element and node objects. Traversing elements and nodes does not need to be done in order.
The DOM parsing method is suitable for smaller XML files. Since it loads the entire XML file into memory for processing, it is not suitable for processing larger XML files. For larger XML files you need to use SAX parsing.
In this tutorial we will read and parse an XML file and use it to create objects. Below is the XML file we will parse.
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>

The content of this XML file is a list of employee information, so we need to create an Employee class to represent employees, and then read the XML file information into the program.
The following is the definition of the Employee class:

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;
    }

}

It should be noted that here I have overridden the toString() method to print out useful information about the employee object. Next, we use DOM parsing in the program to read the XML file to obtain the Employee object list.
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();
    }

}

The program output is as follows:

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

In actual circumstances, we must first verify the legality of the XML file before parsing the XML file. Learn how Use XSD to validate XML files.

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DOM XML parsing method is the easiest to understand. It reads the XML file into memory as a Document object, and then you Different element and node objects can be easily traversed. Traversing elements and nodes does not need to be done in order.
The DOM parsing method is suitable for smaller XML files. Since it loads the entire XML file into memory for processing, it is not suitable for processing larger XML files. For larger XML files you need to use SAX parsing.
In this tutorial we will read and parse an XML file and use it to create objects. Below is the XML file we will parse.
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>

The content of this XML file is a list of employee information, so we need to create an Employee class to represent employees, and then read the XML file information into the program.
The following is the definition of the Employee class:

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;
    }

}

It should be noted that here I have overridden the toString() method to print out useful information about the employee object. Next, we use DOM parsing in the program to read the XML file to obtain the Employee object list.
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();
    }

}

The program output is as follows:

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

In actual circumstances, we must verify the legality of the XML file before parsing it. Learn how Use XSD to validate XML files.

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