Treat XPath Only Using Library Provided by Java SDK

Have you ever treated XML only using library provided in Java SDK?
I think many people use external library for treating XML in Java.
To be honest, I would prefer to use JDom ;P
But I think it's good thing to know how to treat XML only using Java SDK.
I will show you small code snippet for treating XML especially from XPath usage.

The classes you should remember for treating XML is:

• DocumentBuilderFactory
• DocumentBuilder
• Document
• XPathFactory
• XPath
• XPathExpression
• XPathConstants
• NodeList
• Node

Oops, a bit quite too much.
Anyway I will show you an example code for reading XML string and select nodes by XPath.

package com.dulesoftware.xpath;

import java.io.IOException;
import java.io.StringReader;

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

public class XPathExample {

    public static void main(String[] args) throws XPathExpressionException, SAXException, IOException, ParserConfigurationException {
        String xmlString = 
                "<root>"
                + "<items id=\"12345\">"
                + "  <item>"
                + "    <name>Java</name>"
                + "  </item>"
                + "  <item>"
                + "    <name>C#</name>"
                + "  </item>"
                + "</items>"
                + "</root>";

        // build Document
        DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document doc = builder.parse(new InputSource(new StringReader(xmlString)));

        // prepare xpath
        XPathFactory xPathfactory = XPathFactory.newInstance();
        XPath xPath = xPathfactory.newXPath();
        
        // xpaths
        XPathExpression itemPathExpr = xPath.compile("/root/items/item");
        XPathExpression itemsIdPathExpr = xPath.compile("/root/items/@id");
        XPathExpression itemNamePathExpr = xPath.compile("name");            // you should not put "/" if you evaluate xpath on child node

        
        // get attribute
        String id = (String)itemsIdPathExpr.evaluate(doc, XPathConstants.STRING);
        System.out.println("id="+id);
        
        // get nodeset
        NodeList items = (NodeList)itemPathExpr.evaluate(doc, XPathConstants.NODESET);
        for(int i = 0, len = items.getLength(); i < len; i++)
        {
            Node item = items.item(i);
            System.out.println("node name="+item.getNodeName());
            
            // get node
            Node name = (Node)itemNamePathExpr.evaluate(item, XPathConstants.NODE);
            System.out.println("child node value=" + name.getTextContent());
        }
        
    }
}

I think code itself is really straight forward and not so bad.
But the disadvantages of the XML library provided by Java SDK which I felt after I wrote this post is:

1. Too much casting
2. can't use foreach to iterate NodeList
3. Always need Factory and newDocument or newXPath - don't you think quite annoying?