XPath and JAXP

XPath is a language for querying XML Documents. Using a certain syntax XPath can retrieve specific node or list of nodes from the XML Document. This tutorial does not explain XPath syntax but shows how to use JAXP to implement XPath querying. The Steps for XPath querying are:

• Obtain the XPath class from XPathFactory. This class provides the environment for querying the XML DOM Document using an XPath expression
• Create the XPath expression String
• Evaluate the XPath expession using the XPath class, the DOM Document and the Xpath expression

Here’s an example that demonstrates it all.

package com.studytrails.xml.jaxp;

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.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

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

public class JaxpXpathExample6 {
	private static String xmlSource = "http://feeds.bbci.co.uk/news/technology/rss.xml?edition=int";

	public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException, XPathExpressionException {
		// create the DOM Document
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document bbcDoc = builder.parse(xmlSource);

		// create the JAXP XPath evaluation environment.
		XPath xpath = XPathFactory.newInstance().newXPath();

		// creat an xpath expression. This example select all nodes with the
		// name 'link' from the root of the document.
		String expression = "//link";
		// get a list of nodes using the xpath environment, DOM Document and the
		// XPath expression. Specify the type of node that is retrived (in this
		// case its a NODESET which is a list of nodes)
		NodeList linkNodes = (NodeList) xpath.evaluate(expression, bbcDoc, XPathConstants.NODESET);
		for (int i = 0; i < linkNodes.getLength(); i++) {
			// System.out.println(linkNodes.item(i).getTextContent());
		}

		// get the element with name item from parent with name 'channel' whose
		// parent is an element with name 'rss'
		expression = "/rss/channel/item";
		NodeList itemNodes = (NodeList) xpath.evaluate(expression, bbcDoc, XPathConstants.NODESET);
		for (int i = 0; i < itemNodes.getLength(); i++) {
			String expression2 = "title";
			// the resulting node of an XPath evaluation can also be the source
			// of another XPath query. In this case we query for all 'title'
			// elements under '/rss/channel/item'
			Node titleInItemNode = (Node) xpath.evaluate(expression2, itemNodes.item(i), XPathConstants.NODE);
			// System.out.println(titleInItemNode.getTextContent());
		}

		// another way to find the title of all item elements
		expression = "//channel/child::item/descendant::title";
		NodeList someNodes = (NodeList) xpath.evaluate(expression, bbcDoc, XPathConstants.NODESET);
		for (int i = 0; i < someNodes.getLength(); i++) {
			System.out.println(someNodes.item(i).getTextContent());
		}

	}
}