XML with Java

Java has comprehensive built-in XML support through the javax.xml package. It supports DOM, SAX, StAX, XSLT transformation, and XML Schema validation — all without external libraries. For advanced needs, third-party libraries like JDOM2 and dom4j offer simpler APIs.

Parsing XML with DOM

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

public class XMLReader {
    public static void main(String[] args) throws Exception {

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(new File("products.xml"));
        doc.getDocumentElement().normalize();

        NodeList products = doc.getElementsByTagName("product");

        for (int i = 0; i < products.getLength(); i++) {
            Element p = (Element) products.item(i);
            String id    = p.getAttribute("id");
            String name  = p.getElementsByTagName("name")
                            .item(0).getTextContent();
            String price = p.getElementsByTagName("price")
                            .item(0).getTextContent();

            System.out.println(id + ": " + name + " — INR " + price);
        }
    }
}

Building XML with Java DOM

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.newDocument();

Element root = doc.createElement("catalog");
doc.appendChild(root);

Element product = doc.createElement("product");
product.setAttribute("id", "P001");

Element name = doc.createElement("name");
name.setTextContent("USB Hub");
product.appendChild(name);
root.appendChild(product);

// Write to file
TransformerFactory tf = TransformerFactory.newInstance();
Transformer transformer = tf.newTransformer();
transformer.transform(new DOMSource(doc), new StreamResult("output.xml"));

Parsing XML with StAX (Pull Parsing)

import javax.xml.stream.*;

XMLInputFactory factory = XMLInputFactory.newInstance();
XMLStreamReader reader = factory.createXMLStreamReader(
    new FileInputStream("products.xml"));

while (reader.hasNext()) {
    int event = reader.next();
    if (event == XMLStreamConstants.START_ELEMENT) {
        System.out.println("Start: " + reader.getLocalName());
    } else if (event == XMLStreamConstants.CHARACTERS) {
        String text = reader.getText().trim();
        if (!text.isEmpty()) System.out.println("Text: " + text);
    }
}
reader.close();

Key Points to Remember

• Java's DocumentBuilder parses XML into a DOM Document object.
• getTextContent() returns the combined text of an element including all descendants.
• Transformer serializes a DOM Document to a file or stream.
• StAX (XMLStreamReader) is Java's pull-parsing model — lower memory than DOM.
• Always call doc.getDocumentElement().normalize() after parsing to clean up whitespace text nodes.