Steps to Using DOM4J

Following are the steps used while parsing a document using DOM4J Parser.

• Import XML-related packages.
• Create a SAXReader.
• Create a Document from a file or stream.
• Get the required nodes using XPath Expression by calling document.selectNodes()
• Extract the root element.
• Iterate over the list of nodes.
• Examine attributes.
• Examine sub-elements.

Import XML-related packages

import java.io.*;

import java.util.*;

import org.dom4j.*;

Create a DocumentBuilder

SAXBuilder saxBuilder = new SAXBuilder();

Create a Document from a file or stream

File inputFile = new File("input.txt");

SAXBuilder saxBuilder = new SAXBuilder();

Document document = saxBuilder.build(inputFile);

Extract the root element

Element classElement = document.getRootElement();

Examine attributes

//returns specific attribute

valueOf("@attributeName"); 

Examine sub-elements

//returns first child node

selectSingleNode("subelementName"); 

Demo Example

Here is the input xml file that we need to parse −

<?xml version = "1.0"?>

<class>

   <student rollno = "393">

      <firstname>dinkar</firstname>

      <lastname>kad</lastname>

      <nickname>dinkar</nickname>

      <marks>85</marks>

   </student>

   <student rollno = "493">

      <firstname>Vaneet</firstname>

      <lastname>Gupta</lastname>

      <nickname>vinni</nickname>

      <marks>95</marks>

   </student>

   <student rollno = "593">

      <firstname>jasvir</firstname>

      <lastname>singn</lastname>

      <nickname>jazz</nickname>

      <marks>90</marks>

   </student>

</class>

DOM4JParserDemo.java

package com.tutorialspoint.xml;

import java.io.File;

import java.util.List;

import org.dom4j.Document;

import org.dom4j.DocumentException;

import org.dom4j.Element;

import org.dom4j.Node;

import org.dom4j.io.SAXReader;

public class DOM4JParserDemo {

   public static void main(String[] args) {

      try {

         File inputFile = new File("input.txt");

         SAXReader reader = new SAXReader();

         Document document = reader.read( inputFile );

         System.out.println("Root element :" + document.getRootElement().getName());

         Element classElement = document.getRootElement();

         List<Node> nodes = document.selectNodes("/class/student" );

         System.out.println("----------------------------");

         for (Node node : nodes) {

            System.out.println("\nCurrent Element :"

               + node.getName());

            System.out.println("Student roll no : " 

               + node.valueOf("@rollno") );

            System.out.println("First Name : "

               + node.selectSingleNode("firstname").getText());

            System.out.println("Last Name : "

               + node.selectSingleNode("lastname").getText());

            System.out.println("First Name : "

               + node.selectSingleNode("nickname").getText());

            System.out.println("Marks : "

               + node.selectSingleNode("marks").getText());

         }

      } catch (DocumentException e) {

         e.printStackTrace();

      }

   }

}

This would produce the following result −

Root element :class

----------------------------

Current Element :student

Student roll no : 

First Name : dinkar

Last Name : kad

First Name : dinkar

Marks : 85

Current Element :student

Student roll no : 

First Name : Vaneet

Last Name : Gupta

First Name : vinni

Marks : 95

Current Element :student

Student roll no : 

First Name : jasvir

Last Name : singn

First Name : jazz

Marks : 90