Working with XML in Java: DOM, SAX, StAX and JAXB — A Complete Guide

Working with XML in Java: DOM, SAX, StAX and JAXB

XML (eXtensible Markup Language) remains one of the key formats for storing and transmitting structured data. In Java, there are several built-in and popular libraries for working with XML. In this article, we will cover all the main approaches: from classic DOM and SAX to modern JAXB.

1. DOM (Document Object Model) — Full Access to the Document

The DOM parser loads the entire XML document into memory as a tree structure. This provides full control over the document: you can read, modify, delete, and add nodes.

Advantages of DOM:

• Random access to any element of the document
• Ability to modify the XML structure
• Intuitive object model

Disadvantages:

• High memory consumption (entire document in RAM)
• Slow performance with large files

Example of using DOM:

import javax.xml.parsers.*;import org.w3c.dom.*;import java.io.*;

public class DomExample {    public static void main(String[] args) throws Exception {        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        DocumentBuilder builder = factory.newDocumentBuilder();        Document document = builder.parse(new File("books.xml"));

        NodeList bookList = document.getElementsByTagName("book");        for (int i = 0; i < bookList.getLength(); i++) {            Element book = (Element) bookList.item(i);            String title = book.getElementsByTagName("title").item(0).getTextContent();            String author = book.getElementsByTagName("author").item(0).getTextContent();            System.out.println(title + " — " + author);        }    }}

2. SAX (Simple API for XML) — Streaming Parsing

SAX is an event-driven parser. It reads XML sequentially and calls callback methods when encountering opening/closing tags, text, or attributes. Memory consumption is minimal.

When to use SAX:

• Huge XML files (hundreds of megabytes)
• Read-only, no modification needed
• Limited device resources

Example of a SAX parser:

import org.xml.sax.*;import org.xml.sax.helpers.*;import javax.xml.parsers.*;

public class SaxExample {    public static void main(String[] args) throws Exception {        SAXParserFactory factory = SAXParserFactory.newInstance();        SAXParser saxParser = factory.newSAXParser();

        DefaultHandler handler = new DefaultHandler() {            boolean isTitle = false;

            public void startElement(String uri, String localName,                                     String qName, Attributes attributes) {                if (qName.equalsIgnoreCase("title")) isTitle = true;            }

            public void characters(char ch[], int start, int length) {                if (isTitle) {                    System.out.println("Title: " + new String(ch, start, length));                    isTitle = false;                }            }        };

        saxParser.parse("books.xml", handler);    }}

3. StAX (Streaming API for XML) — Convenient Streaming Parsing

StAX is a compromise between DOM and SAX. It also works in streaming mode but provides a more convenient pull interface (you request the next element yourself).

Two ways to work with StAX:

• XMLStreamReader — for reading
• XMLStreamWriter — for writing

import javax.xml.stream.*;import java.io.*;

public class StaxExample {    public static void main(String[] args) throws Exception {        XMLInputFactory factory = XMLInputFactory.newInstance();        XMLStreamReader reader = factory.createXMLStreamReade