XPath (XML Path Language) is a language for selecting / searching nodes from an XML document. Java 5 introduced the javax.xml.xpath package which provides a XPath library.

The following explains how to use XPath to query an XML document via Java.

The following explains how to use XPath. Create a new Java project called "UsingXPath".

Create the following xml file.

				
<?xml version="1.0" encoding="UTF-8"?>
<people>
	<person>
		<firstname>Lars</firstname>
		<lastname>Vogel</lastname>
		<city>Heidelberg</city>
	</person>
	<person>
		<firstname>Jim</firstname>
		<lastname>Knopf</lastname>
		<city>Heidelberg</city>
	</person>
	<person>
		<firstname>Lars</firstname>
		<lastname>Strangelastname</lastname>
		<city>London</city>
	</person>
	<person>
		<firstname>Landerman</firstname>
		<lastname>Petrelli</lastname>
		<city>Somewhere</city>
	</person>
	<person>
		<firstname>Lars</firstname>
		<lastname>Tim</lastname>
		<city>SomewhereElse</city>
	</person>
</people>

			

Create a new package "myxml" and a new Java class "QueryXML".

				
package myxml;

import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class QueryXML {
	public void query() throws ParserConfigurationException, SAXException,
			IOException, XPathExpressionException {
		// Standard of reading a XML file
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		factory.setNamespaceAware(true);
		DocumentBuilder builder;
		Document doc = null;
		XPathExpression expr = null;
		builder = factory.newDocumentBuilder();
		doc = builder.parse("person.xml");

		// Create a XPathFactory
		XPathFactory xFactory = XPathFactory.newInstance();

		// Create a XPath object
		XPath xpath = xFactory.newXPath();

		// Compile the XPath expression
		expr = xpath.compile("//person[firstname='Lars']/lastname/text()");
		// Run the query and get a nodeset
		Object result = expr.evaluate(doc, XPathConstants.NODESET);
		
		// Cast the result to a DOM NodeList
		NodeList nodes = (NodeList) result;
		for (int i=0; i<nodes.getLength();i++){
			System.out.println(nodes.item(i).getNodeValue());
		}
		
		// New XPath expression to get the number of people with name lars
		expr = xpath.compile("count(//person[firstname='Lars'])");
		// Run the query and get the number of nodes
		Double number = (Double) expr.evaluate(doc, XPathConstants.NUMBER);
		System.out.println("Number of objects " +number);
		
		// Do we have more then 2 people with name lars?
		expr = xpath.compile("count(//person[firstname='Lars']) >2");
		// Run the query and get the number of nodes
		Boolean check = (Boolean) expr.evaluate(doc, XPathConstants.BOOLEAN);
		System.out.println(check);
		
	}

	public static void main(String[] args) throws XPathExpressionException, ParserConfigurationException, SAXException, IOException {
		QueryXML process = new QueryXML();
		process.query();
	}
}