Java SAX Parser – Read XML Example

SAX parser, or Simple API for XML has been around for many years and was originally a development lead by David Megginson before the turn of the millennium. In those days, you had to download the Java version of SAX from David’s personal web site. This developed into the SAX Project before finally being added to Java Standard Edition 1.4.

SAX is a streaming interface for XML, which means that applications using SAX receive event notifications about the XML document being processed an element, and attribute, at a time in sequential order starting at the top of the document, and ending with the closing of the ROOT element. This means that it’s extremely efficient at processing XML in linear time without placing too many demands upon system memory.

Lets create a demo program to read xml file with SAX parser to understand fully.

1. Prepare xml file to be parsed

This xml file contains xml attributes also along with xml elements.

<users>
	<user id="100">
		<firstname>Tom</firstname>
		<lastname>Hanks</lastname>
	</user>
	<user id="101">
		<firstname>Lokesh</firstname>
		<lastname>Gupta</lastname>
	</user>
	<user id="102">
		<firstname>HowToDo</firstname>
		<lastname>InJava</lastname>
	</user>
</users>

2. Create model class

package com.howtodoinjava.xml.sax;

/**
 * Model class. Its instances will be populated using SAX parser.
 * */
public class User
{
	//XML attribute id
	private int id;
	//XML element fisrtName
	private String firstName;
	//XML element lastName
	private String lastName;

	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getFirstName() {
		return firstName;
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	public String getLastName() {
		return lastName;
	}
	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	@Override
	public String toString() {
		return this.id + ":" + this.firstName +  ":" +this.lastName ;
	}
}

3. Build the handler by extending DefaultParser

Below the code for parse handler. I have put additional information in code comments. Still, is you have any query, drop me a comment.

package com.howtodoinjava.xml.sax;

import java.util.ArrayList;
import java.util.Stack;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

public class UserParserHandler extends DefaultHandler
{
	//This is the list which shall be populated while parsing the XML.
    private ArrayList userList = new ArrayList();

    //As we read any XML element we will push that in this stack
    private Stack elementStack = new Stack();

    //As we complete one user block in XML, we will push the User instance in userList
    private Stack objectStack = new Stack();

    public void startDocument() throws SAXException
    {
        //System.out.println("start of the document   : ");
    }

    public void endDocument() throws SAXException
    {
        //System.out.println("end of the document document     : ");
    }

    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException
    {
    	//Push it in element stack
        this.elementStack.push(qName);

        //If this is start of 'user' element then prepare a new User instance and push it in object stack
        if ("user".equals(qName))
        {
            //New User instance
        	User user = new User();

            //Set all required attributes in any XML element here itself
            if(attributes != null && attributes.getLength() == 1)
            {
            	user.setId(Integer.parseInt(attributes.getValue(0)));
            }
            this.objectStack.push(user);
        }
    }

    public void endElement(String uri, String localName, String qName) throws SAXException
    {
    	//Remove last added  element
        this.elementStack.pop();

        //User instance has been constructed so pop it from object stack and push in userList
        if ("user".equals(qName))
        {
            User object = this.objectStack.pop();
            this.userList.add(object);
        }
    }

    /**
     * This will be called everytime parser encounter a value node
     * */
    public void characters(char[] ch, int start, int length) throws SAXException
    {
        String value = new String(ch, start, length).trim();

        if (value.length() == 0)
        {
            return; // ignore white space
        }

        //handle the value based on to which element it belongs
        if ("firstName".equals(currentElement()))
        {
            User user = (User) this.objectStack.peek();
            user.setFirstName(value);
        }
        else if ("lastName".equals(currentElement()))
        {
            User user = (User) this.objectStack.peek();
            user.setLastName(value);
        }
    }

    /**
     * Utility method for getting the current element in processing
     * */
    private String currentElement()
    {
        return this.elementStack.peek();
    }

    //Accessor for userList object
    public ArrayList getUsers()
    {
    	return userList;
    }
}

4. SAX parser to read XML file

package com.howtodoinjava.xml.sax;

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

import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.XMLReaderFactory;

public class UsersXmlParser
{
	public ArrayList parseXml(InputStream in)
	{
		//Create a empty link of users initially
		ArrayList<user> users = new ArrayList</user><user>();
		try
		{
			//Create default handler instance
			UserParserHandler handler = new UserParserHandler();

			//Create parser from factory
			XMLReader parser = XMLReaderFactory.createXMLReader();

			//Register handler with parser
			parser.setContentHandler(handler);

			//Create an input source from the XML input stream
			InputSource source = new InputSource(in);

			//parse the document
			parser.parse(source);

			//populate the parsed users list in above created empty list; You can return from here also.
			users = handler.getUsers();

		} catch (SAXException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {

		}
		return users;
	}
}

5) Test SAX parser

Lets write some code to test whether our handler is actually working.

package com.howtodoinjava.xml.sax;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.ArrayList;

public class TestSaxParser
{
	public static void main(String[] args) throws FileNotFoundException
	{
		//Locate the file
		File xmlFile = new File("D:/temp/sample.xml");

		//Create the parser instance
		UsersXmlParser parser = new UsersXmlParser();

		//Parse the file
		ArrayList users = parser.parseXml(new FileInputStream(xmlFile));

		//Verify the result
		System.out.println(users);
	}
}

Output:
[100:Tom:Hanks, 101:Lokesh:Gupta, 102:HowToDo:InJava]

Happy Learning !!