Java SAX Parser – Read XML Example

SAX Parser or, Simple API for XML, has been around for many years and was originally a development led 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 website. 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.

1. Setup

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 Java POJO

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;

        //Setters, getters
}

3. SAX Event Handler

Below is the code for the parsing handler. I have put additional information in the code comments. Still, if you have any queries, 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. Reading the XML File

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) Demo

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

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);
        }
}

Program output.

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

Happy Learning !!