Sax Parsing in android

Basic SAX

There are currently two published versions of the SAX API. We'll use version 2 (see Resources) for our examples. Version 2 uses different class and method names than version 1, but the structure of the code is the same.

SAX is an API, not a parser, so this code is generic across XML parsers. To get the examples to run, you will need to access an XML parser that supports SAX v2. I use Apache's Xerces parser. (See Resources.) Review your parser's getting-started guide for specifics on invoking a SAX parser.

The SAX API specification is pretty straightforward. In includes many details, but its primary task is to create a class that implements the ContentHandler interface, a callback interface used by XML parsers to notify your program of SAX events as they are found in the XML document.

The SAX API also conveniently supplies a DefaultHandler implementation class for the ContentHandler interface.

Once you've implemented the ContentHandler or extended the DefaultHandler, you need only direct the XML parser to parse a particular document.

Our first example extends the DefaultHandler to print each SAX event to the console. This will give you a feel for what SAX events will be generated and in what order.

To get started, here's the sample XML document we will use in our first example:

<?xml version="1.0"?>
<simple date="7/7/2000" >
   <name> Bob </name>
   <location> New York </location>
</simple>

Next, we see the source code for XML mapping code of the first example:

import org.xml.sax.*;
import org.xml.sax.helpers.*;
import java.io.*;

public class Example1 extends DefaultHandler {


   // Override methods of the DefaultHandler class
   // to gain notification of SAX Events.
   //
        // See org.xml.sax.ContentHandler for all available events.
   //
   public void startDocument( ) throws SAXException {
      System.out.println( "SAX Event: START DOCUMENT" );
   }

   public void endDocument( ) throws SAXException {
      System.out.println( "SAX Event: END DOCUMENT" );
   }

   public void startElement( String namespaceURI,
              String localName,
              String qName,
              Attributes attr ) throws SAXException {
         System.out.println( "SAX Event: START ELEMENT[ " +
                &nbs p; localName + " ]" );

      // Also, let's print the attributes if
      // there are any...
                for ( int i = 0; i < attr.getLength(); i++ ){
                &nbs p;  System.out.println( " ATTRIBUTE: " +
                &nbs p; attr.getLocalName(i) +
                &nbs p; " VALUE: " +
                &nbs p; attr.getValue(i) );
      }

   }

   public void endElement( String namespaceURI,
              String localName,
              String qName ) throws SAXException {
      System.out.println( "SAX Event: END ELEMENT[ " +
                &nbs p; localName + " ]" );
   }

   public void characters( char[] ch, int start, int length )
                &nbs p; throws SAXException {

      System.out.print( "SAX Event: CHARACTERS[ " );

      try {
         OutputStreamWriter outw = new OutputStreamWriter(System.out);
         outw.write( ch, start,length );
         outw.flush();
      } catch (Exception e) {
         e.printStackTrace();
      }

      System.out.println( " ]" );

   }


   public static void main( String[] argv ){

      System.out.println( "Example1 SAX Events:" );
      try {

         // Create SAX 2 parser...
         XMLReader xr = XMLReaderFactory.createXMLReader();

         // Set the ContentHandler...
         xr.setContentHandler( new Example1() );

            // Parse the file...
         xr.parse( new InputSource(
               new FileReader( "Example1.xml" )) );


      }catch ( Exception e ) {
         e.printStackTrace();
      }

   }

}

Finally, here is the output generated by running the first example with our sample XML document:

Example1 SAX Events:
SAX Event: START DOCUMENT
SAX Event: START ELEMENT[ simple ]
   ATTRIBUTE: date VALUE: 7/7/2000
SAX Event: CHARACTERS[
    ]
SAX Event: START ELEMENT[ name ]
SAX Event: CHARACTERS[ Bob ]
SAX Event: END ELEMENT[ name ]
SAX Event: CHARACTERS[
    ]
SAX Event: START ELEMENT[ location ]
SAX Event: CHARACTERS[ New York ]
SAX Event: END ELEMENT[ location ]
SAX Event: CHARACTERS[
 ]
SAX Event: END ELEMENT[ simple ]
SAX Event: END DOCUMENT

As you can see, the SAX parser will call the appropriate ContentHandler method for every SAX event it discovers in the XML document.