Java XPath Get Attribute Value from XML

Many times we need to parse an XML file and extract information from it. For example, read attribute value of an XML element with xpath. In this Java XPath tutorial, learn to get attribute value from an XML String.

I am using jdom and jaxen. These are other plenty open source APIs available also, but the idea remains the same.

Java program to get value from in Java using XPath

Below given Java program create a DOM object from supplied XML string. It then applies the XPATH expression using XPath.selectNodes() method.

Method returns list of Element instances which are result of evaluating XPath expression. You can iterate the list and use the results.

package com.howtodoinjava.xml;

import java.io.IOException;
import java.io.StringReader;
import java.util.ArrayList;

import org.jdom.Document;
import org.jdom.Element;
import org.jdom.JDOMException;
import org.jdom.input.SAXBuilder;
import org.jdom.xpath.XPath;

public class XmlAttributesUsingXPathExample
{
	@SuppressWarnings("unchecked")
	public static void main(String[] args) throws JDOMException, IOException
	{
		Document doc = new SAXBuilder(false).build(new StringReader(new String(
                                               <users>	" +
													<user id='13423'>" +
														<firstname>Andre</firstname>" +
													</user>" +
													<user id='32424'>" +
														<firstname>Peter</firstname>" +
													</user> " +
													<user id='543534'>" +
														<firstname>Sandra</firstname>" +
													</user>" +
												</users>")));

		//Build the xpath expression
		XPath xpathExpression = XPath.newInstance("//*[@id]");

		//Apply xpath and fetch all matching nodes
		ArrayList<Element> userIds =  (ArrayList<Element>) xpathExpression.selectNodes(doc);

		//Iterate over naodes and print the value
		for (int i = 0; i < userIds.size(); i++)
        {
        	System.out.println((userIds.get(i)).getAttributeValue("id").trim());
        }
	}
}

Program output.

13423
32424
543534

java.lang.ClassCastException: org.jdom.Document cannot be cast to org.w3c.dom.Node
at com.sun.org.apache.xpath.internal.jaxp.XPathExpressionImpl.eval(XPathExpressionImpl.java:116)
at com.sun.org.apache.xpath.internal.jaxp.XPathExpressionImpl.eval(XPathExpressionImpl.java:98)
at com.sun.org.apache.xpath.internal.jaxp.XPathExpressionImpl.evaluate(XPathExpressionImpl.java:180)

Happy Learning !!