[jdom-interest] making SAXHandler class public?

[Jan Peter Hecking]

Hi!

A while ago I asked whether it would be possible to turn the SAXHandler
class used by the SAXBuilder internaly into a public class. Well, I
went ahead and did so in my JDOM source tree. In the attached program
one can see why I think this change is useful: there's no need any more
for those pesky Piped(Input|Output)Streams when trying to transform a
JDOM document into another JDOM document using the TrAX API. As the
J2SE API docs state:

------------------------------ snip --------------------------------
[...] Typically, data is read from a PipedInputStream object by one
thread and data is written to the corresponding PipedOutputStream
by some other thread. Attempting to use both objects from a single
thread is not recommended, as it may deadlock the thread. [...]
------------------------------ snip --------------------------------

I had this problem and using the SAXHandler directly is the most elegant
solution to this problem I think. It is probably a lot faster, too.

If there is no fundamental problem with turning the SAXHandler into a
public class I would like to suggest this change for the JDOM API.
No changes to the SAXHandler class or the SAXBuilder class are
necessary!

bye,
Jan

-- 
Jan Peter Hecking                  jhecking at netgaroo.com
University of Rostock     Department of Computer Science
Homepage: http://www.informatik.uni-rostock.de/~jhecking
-------------- next part --------------
import org.jdom.Document;
import org.jdom.input.SAXHandler;
import org.jdom.output.SAXOutputter;

import org.xml.sax.XMLReader;
import org.xml.sax.helpers.XMLReaderFactory;

import javax.xml.transform.Templates;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.sax.SAXResult;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.sax.TemplatesHandler;
import javax.xml.transform.sax.TransformerHandler;

/**
 * Helper class with one static method to allow clients to transform JDOM
 * documents using XSLT.
 */
public class XsltTransformer
{
    private static SAXOutputter saxOutputter;
    private static SAXTransformerFactory saxTFactory;
    private static TemplatesHandler templatesHandler;
    private static XMLReader reader;

    static{
        try{
            // don't forget to set the ContentHandler before using
            // the outputter!
            saxOutputter = new SAXOutputter( null );
            saxTFactory = (SAXTransformerFactory) TransformerFactory.newInstance();
            templatesHandler = saxTFactory.newTemplatesHandler();
            reader = XMLReaderFactory.createXMLReader();
            reader.setContentHandler( templatesHandler );
        }
        catch( Exception e ){
            e.printStackTrace();
            //System.exit( -1 );
        }
    }

    /**
     * Transforms a JDOM document into another JDOM document using the given
     * stylesheet.
     */
    public static Document transform( Document sourceDoc, String stylesheet )
        throws XsltTransformerException
    {
        try{
            reader.parse( stylesheet );

            Templates templates = templatesHandler.getTemplates();
            TransformerHandler handler = saxTFactory.newTransformerHandler(
                    templates );

            Document targetDoc = new Document( null );
            // had to turn SAXHandler into a public class to use it here:
            handler.setResult( new SAXResult( new SAXHandler( targetDoc ) ) );

            saxOutputter.setContentHandler( handler );
            saxOutputter.output( sourceDoc );

            return targetDoc;
        }
        catch( Exception e ){
            throw new XsltTransformerException( e );
        }
    }//transform()
}//XsltTransformer
-------------- next part --------------
/**
 * Encapsulates all Exceptions that can be thrown by the
 * XsltTransformer.transform() method.
 */
public class XsltTransformerException
    extends Exception
{
    private Exception nestedException;

    public XsltTransformerException( Exception e )
    {
        super( e.getMessage() );
        nestedException = e;
    }//XsltTransformerException

    public Exception getNestedException()
    {
        return nestedException;
    }//getNestedException()
}//XsltTransformerException