Parsing XML files in Java using javax.xml.parsers.DocumentBuilder

Background

If you want to read xml files and process tag and attributes then there is a smarter way to do it than just reading the file line by line. That is exactly what we are going to see in this post.

To the Code.....

Assume we have the following data.xml file in the root directory of the project with following contents - 

<ROOT>
    <data key="name" value="John"></data>
    <data key="age" value="23"></data>
    <data key="sex" value="male"></data>
</ROOT>

Our goal is to parse this file and print key and value in an efficient manner. We do it the following way - 

import java.io.File;
import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

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

/**
 * 
 * @author athakur
 *
 */
public class XMLParser {
    
    public static void main(String args[]) throws IOException, ParserConfigurationException, SAXException
    {
        File file = new File("data.xml");
        DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document doc = db.parse(file);
        NodeList nodes = doc.getElementsByTagName("data");
        for ( int i = 0; i < nodes.getLength(); i++) 
        {
            Element element = (Element) nodes.item(i);
            String key = element.getAttribute("key");
            String value = element.getAttribute("value");    
            System.out.println("Key : " + key + " || Value : " + value);
        }
    }
}

and the output is as expected - 

Key : name || Value : John
Key : age || Value : 23
Key : sex || Value : male

Easy... wasn't it? Using DocumentBuilder makes parsing xml files easy.

NOTE : The XML file should have only one root element and can have multiple child elements. If this is not satisfied you will get following Exception

org.xml.sax.SAXParseException: The markup in the document following the root element must be well-formed.

In case of such cases (multiple root elements) how can we parse the XML? I have explained the same in separate post (See Related Links section below)

Parsing XML String

For parsing Simple XML strings you can do - 

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

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

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


public class StringXMLParser {
    
    public static void main(String args[]) throws SAXException, IOException, ParserConfigurationException {
        
            String xmlString = "<records><employee><name>Aniket</name><title>Software Developer</title></employee></records>";
            
            DocumentBuilder db = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            Document doc = db.parse(new InputSource(new StringReader(xmlString)));
            
            NodeList nodes = doc.getElementsByTagName("employee");

            for (int i = 0; i < nodes.getLength(); i++) {
              Element element = (Element) nodes.item(i);

              NodeList name = element.getElementsByTagName("name");
              Element line = (Element) name.item(0);
              System.out.println("Name: " + line.getFirstChild().getNodeValue());

              NodeList title = element.getElementsByTagName("title");
              line = (Element) title.item(0);
              System.out.println("Title: " + line.getFirstChild().getNodeValue());
            }
    }
}

Related Links

• Resolving "The markup in the document following the root element must be well-formed" Exception