• You could write your own program to process an XML document.
• Two APIs make these programs easy to write in Java: SAX, DOM.
• SAX walks through an XML document. It generates events for each part of a document.
• In your Java program, you can provide an object to handle these events.
• DOM builds a data structure representing an XML document.
• Your Java program can wander around the data structure at will.

• Suppose we want to write a Java program to transform some XML into HTML.
• Although DOM could be used to do this, makes more sense to use SAX.
• Many software developers provide SAX.
• Code you write that uses SAX is the same except for creating an instance of the SAX parser.
• Suppose we use the Xerces parser from the Apache Software Foundation:

XMLReader tXMLReader = new org.apache.xerces.parsers.SAXParser();

• We also need to create the handler that is to handle the events generated by the SAX parser:

Handler tHandler = new Handler();

• This object then needs to be registered with the SAX parser:

tXMLReader.setContentHandler(tHandler);

• Then the parser is let loose on the document:

FileReader tFileReader = new FileReader("consumables.xml");
InputSource tInputSource = new InputSource(tFileReader);
tXMLReader.parse(tInputSource);

• It is the Handler class that is used to state what should happen when each event arises.
• It has to override the methods of the DefaultHandler class (which has methods that do nothing).
• For example, consider:

public class Handler extends DefaultHandler
{
   public void startElement(String pURI, String pLocalName,
                            String pQualifiedName, Attributes pAttributes)
   {
      System.out.println(pLocalName);
   }
}

• This Handler class would cause the name of each element to be output when the start tag of the element is parsed.

• The full code of a program that produces HTML from the consumables.xml file is given at http://www.dur.ac.uk/barry.cornelius/java/xml.processing/code/ConvertConsumables.java and http://www.dur.ac.uk/barry.cornelius/java/xml.processing/code/Handler.java.