XSLT SAXParser which inserts user trace calls in xsl:template instructions.

TraceXmlReader.java

package rocks.xml.saxontrace;

import org.apache.xerces.parsers.SAXParser;
import org.apache.xerces.util.AugmentationsImpl;
import org.apache.xerces.util.XMLAttributesImpl;
import org.apache.xerces.xni.Augmentations;
import org.apache.xerces.xni.QName;
import org.apache.xerces.xni.XMLAttributes;
import org.apache.xerces.xni.XNIException;

public class TraceXmlReader extends SAXParser {
    private static final QName TEMPLATE_NAME = new QName("xsl", "template", "xsl:template", "http://www.w3.org/1999/XSL/Transform");
    private static final QName SEQUENCE_NAME = new QName("xsl", "sequence", "xsl:sequence", "http://www.w3.org/1999/XSL/Transform");
    private static final QName SELECT_NAME = new QName(null, "select", "value", "http://www.w3.org/1999/XSL/Transform");

    @Override
    public void startElement(QName element, XMLAttributes attributes, Augmentations augs) throws XNIException {
        super.startElement(element, attributes, augs);
        if (isMatchTemplate(element, attributes)) {
            sequenceWithTraceCall(attributes);
        }
    }

    private boolean isMatchTemplate(QName element, XMLAttributes attributes) {
        return TEMPLATE_NAME.equals(element) && attributes.getIndex("match") != -1;
    }

    /*
     * Inserts xsl:sequence instruction with a trace call.
     *
     * The trace info contains the match pattern. For instance,
     * <xsl:sequence select="trace(., 'attribute() | node()')"/>
     */
    private void sequenceWithTraceCall(XMLAttributes attributes) {
        XMLAttributesImpl sequenceAttributes = new XMLAttributesImpl();
        String selectValue = String.format("trace((), '%s')", attributes.getValue("match"));
        sequenceAttributes.addAttribute(SELECT_NAME, "CDATA", selectValue);

        super.startElement(SEQUENCE_NAME, sequenceAttributes, new AugmentationsImpl());
        super.endElement(SEQUENCE_NAME, new AugmentationsImpl());
    }
}