SAXBrowser.java - SAX Based XML Browser

JDK Tutorials - Herong's Tutorial Examples

∟SAXBrowser.java - SAX Based XML Browser

This section provides a tutorial example on how to write an XML file browser, SAXBrowser.java. This browser implements some event handler methods provided by the SAX interface.

Let's build a simple SAX based XML browser by handling the events in the ContentHandler interface:

/* SAXBrowser.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.io.File;
import java.io.IOException;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.ParserConfigurationException;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
class SAXBrowser {
   public static void main(String[] args) {
      try {
         File x = new File(args[0]);
         SAXParserFactory f = SAXParserFactory.newInstance();
         SAXParser p = f.newSAXParser();
         DefaultHandler h = new MyContentHandler();
         p.parse(x,h);
      } catch (ParserConfigurationException e) {
         System.out.println(e.toString());
      } catch (SAXException e) {
         System.out.println(e.toString());
      } catch (IOException e) {
         System.out.println(e.toString());
      }
   }
   private static class MyContentHandler extends DefaultHandler {
      static String p = "_";
      public void startDocument() throws SAXException {
         System.out.println("Starting document...");
      }
      public void endDocument() throws SAXException {
         System.out.println("Ending document...");
      }
      public void startElement(String ns, String sName, String qName,
         Attributes attrs) throws SAXException {
         String eName = sName;
         if (sName.equals("")) eName = qName;
         System.out.println("e"+p+eName);
         if (attrs!=null) {
            for (int i=0; i<attrs.getLength(); i++) {
               String aName = attrs.getLocalName(i);
               if (aName.equals("")) aName = attrs.getQName(i);
               System.out.println("a"+p+" "+aName+"="
                  +attrs.getValue(i));
            }
         }
         p = p + "_";
      }
      public void endElement(String ns, String sName, String qName)
         throws SAXException {
         p = p.replaceFirst("__", "_");
      }
      public void characters(char buf[], int offset, int len)
         throws SAXException {
         String s = new String(buf, offset, len);
         System.out.println("c"+p+s);
      }
      public void ignorableWhitespace(char buf[], int offset, int len)
         throws SAXException {
         String s = new String(buf, offset, len);
         System.out.println("i"+p+s);
      }
   }
}

Note that:

I cheated a little bit. Instead of implementing the ContentHandler interface directly, I extended the DefaultHandler class, which implements handling methods for all events (by doing nothing). In this way, I only need to override the handling methods that I am interested in.
"_" character is used to indent sub-elements in nested elements.

Let's try this with hello.xml:

<?xml version="1.0"?>
<body>Hello world!</body>

Run java SAXBrowser hello.xml, I got:

herong> java SAXBrowser.java hello.xml

Starting document...
e_body
c__Hello world!
Ending document...

Excellent. The program seems to be working.

Now, let's try it with user.xml:

<?xml version="1.0"?>
<user status="active">
 <!-- This is not a real user. -->
 <first_name>John</first_name>
 <last_name>Smith</last_name>
</user>

Run SAXBrowser with newer versions of JDK, I got:

herong> java SAXBrowser user.xml

Starting document...
e_user
a_ status=active
c__

c__

e__first_name
c___John
c__

e__last_name
c___Smith
c__

Ending document...

The output has a number "characters" entries with just line breaks. Here is how to read them:

The first "c__\n" after "a_ status=active" represents the line break before the comment line in the XML document.
The second "c__\n" after "a_ status=active" represents the line break after the comment line in the XML document.
The "c__\n" after "c___John" represents the line break after the "first_name" line in the XML document.
The "c__\n" after "c___Smith" represents the line break after the "last_name" line in the XML document.

But I ran SAXBrowser on user.xml with JDK 1.4, I got:

herong> \j2sdk1.4.1_01\bin\java SAXBrowser user.xml

Starting document...
e_user
a_ status=active
c__
c__

c__
c__
c__

c__
e__first_name
c___John
c__
c__

c__
e__last_name
c___Smith
c__
c__

Ending document...

In JDK 1.4, the parser fired so many "characters()" events. It looks like the parser didn't group the space character, line feed, and cartridge return into a single char[] and fire one "characters()" event. It fired multiple events, one per character.