Home arrow XML arrow Page 5 - XML Parsing With SAX and Xerces (part 1)

Sweeping Up The Mess - XML

So you've already seen how Perl and PHP handle XML data. But you're a Real Programmer, and Real Programmers don't waste time with scripting languages. Nope, you need something a little more powerful, something with more horsepower under the hood. Something written in Java. Something like Xerces.

TABLE OF CONTENTS:
  1. XML Parsing With SAX and Xerces (part 1)
  2. Playing The SAX
  3. Reaching For The Nailgun
  4. Under The Microscope
  5. Sweeping Up The Mess
  6. Diving Deeper
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 16
January 28, 2002

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The example you just saw contains a whole bunch of callback method definitions that don't actually do anything. This merely clutters your code while adding very little by way of functionality. Which is why the guys behind Xerces came up with an alternative to the ContentHandler interface, called the DefaultHandler interface.

This "helper" class implements the ContentHandler class, along with all of its callbacks; however, these callbacks do nothing by default. The developer can then selectively override these empty callbacks as per the requirements of the application - this is more efficient in general, and also results in cleaner code.

Take a look at this version of the previous example, this one built on the DefaultHandler class instead of the ContentHandler class:

import org.apache.xerces.parsers.SAXParser; import org.xml.sax.*; import org.xml.sax.helpers.DefaultHandler; import java.io.*; public class MySecondSaxApp extends DefaultHandler { // constructor public MySecondSaxApp (String xmlFile) { // create a Xerces SAX parser SAXParser parser = new SAXParser(); // set the content handler parser.setContentHandler(this); // parse the document try { parser.parse(xmlFile); } catch (SAXException e) { System.err.println (e); } catch (IOException e) { System.err.println (e); } } // call when start elements are found public void startElement (String uri, String local, String qName, Attributes atts) { System.out.println ("Found element: " + local); } // everything starts here public static void main (String[] args) { MySecondSaxApp mySecondExample = new MySecondSaxApp(args[0]); } } This example is much more readable than the previous one, primarily because the entire set of callbacks defined previously are conspicuously absent here. As stated above, these empty callbacks are already provided by the DefaultHandler class; a developer only needs to redefine those which are actually required by the application. Note, though, that extending the DefaultHandler class requires you to add one more item to your list of includes at the top of the program: [code] import org.xml.sax.helpers.DefaultHandler;
Here's the output:

Found element: inventory Found element: item Found element: id Found element: name Found element: supplier Found element: cost Found element: quantity Found element: item Found element: id Found element: name Found element: supplier Found element: cost Found element: quantity


 
 
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