org.apache.xpath.XPathContext Java Examples

/**
   * Copy the template contents into the result tree.
   * The content of the xsl:template element is the template
   * that is instantiated when the template rule is applied.
   *
   * @param transformer non-null reference to the the current transform-time state.
   *
   * @throws TransformerException
   */
  public void execute(
          TransformerImpl transformer)
            throws TransformerException
  {
    XPathContext xctxt = transformer.getXPathContext();
    
    xctxt.pushRTFContext();

      // %REVIEW% commenting out of the code below.
//    if (null != sourceNode)
//    {
      transformer.executeChildTemplates(this, true);
//    }
//    else  // if(null == sourceNode)
//    {
//      transformer.getMsgMgr().error(this,
//        this, sourceNode,
//        XSLTErrorResources.ER_NULL_SOURCENODE_HANDLEAPPLYTEMPLATES);
//
//      //"sourceNode is null in handleApplyTemplatesInstruction!");
//    }

    xctxt.popRTFContext();
    }
 

/**
 * Cast result object to a result tree fragment.
 *
 * @param support XPath context to use for the conversion
 *
 * @return the objec as a result tree fragment.
 */
public int rtf(XPathContext support)
{

  int result = rtf();

  if (DTM.NULL == result)
  {
    DTM frag = support.createDocumentFragment();

    // %OPT%
    frag.appendTextChild(str());

    result = frag.getDocument();
  }

  return result;
}
 

/**
 * Get the match score of the given node.
 *
 * @param xctxt The XPath runtime context.
 * @param context The node to be tested.
 *
 * @return {@link org.apache.xpath.patterns.NodeTest#SCORE_NODETEST},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_NONE},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_NSWILD},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_QNAME}, or
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_OTHER}.
 *
 * @throws javax.xml.transform.TransformerException
 */
public double getMatchScore(XPathContext xctxt, int context)
        throws javax.xml.transform.TransformerException
{

  xctxt.pushCurrentNode(context);
  xctxt.pushCurrentExpressionNode(context);

  try
  {
    XObject score = execute(xctxt);

    return score.num();
  }
  finally
  {
    xctxt.popCurrentNode();
    xctxt.popCurrentExpressionNode();
  }

  // return XPath.MATCH_SCORE_NONE;
}
 

/**
 * Execute an expression in the XPath runtime context, and return the
 * result of the expression.
 *
 *
 * @param xctxt The XPath runtime context.
 * @param handler The target content handler.
 *
 * @return The result of the expression in the form of a <code>XObject</code>.
 *
 * @throws javax.xml.transform.TransformerException if a runtime exception
 *         occurs.
 * @throws org.xml.sax.SAXException
 */
public void executeCharsToContentHandler(
        XPathContext xctxt, org.xml.sax.ContentHandler handler)
          throws javax.xml.transform.TransformerException,
                 org.xml.sax.SAXException
{
  LocPathIterator clone = (LocPathIterator)m_clones.getInstance();

  int current = xctxt.getCurrentNode();
  clone.setRoot(current, xctxt);
  
  int node = clone.nextNode();
  DTM dtm = clone.getDTM(node);
  clone.detach();
	
  if(node != DTM.NULL)
  {
    dtm.dispatchCharactersEvents(node, handler, false);
  }
}
 

/**
 * Execute an expression in the XPath runtime context, and return the 
 * result of the expression.
 *
 *
 * @param xctxt The XPath runtime context.
 *
 * @return The result of the expression in the form of a <code>XObject</code>.
 *
 * @throws javax.xml.transform.TransformerException if a runtime exception 
 *         occurs.
 */
public void executeCharsToContentHandler(XPathContext xctxt, 
                                            ContentHandler handler)
  throws javax.xml.transform.TransformerException,
         org.xml.sax.SAXException
{
  if(Arg0IsNodesetExpr())
  {
    int node = getArg0AsNode(xctxt);
    if(DTM.NULL != node)
    {
      DTM dtm = xctxt.getDTM(node);
      dtm.dispatchCharactersEvents(node, handler, true);
    }
  }
  else
  {
    XObject obj = execute(xctxt);
    obj.dispatchCharactersEvents(handler);
  }
}
 

/**
 * Execute this pattern step, including predicates.
 *
 *
 * @param xctxt XPath runtime context.
 * @param currentNode The current node context.
 *
 * @return {@link org.apache.xpath.patterns.NodeTest#SCORE_NODETEST},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_NONE},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_NSWILD},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_QNAME}, or
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_OTHER}.
 *
 * @throws javax.xml.transform.TransformerException
 */
public XObject execute(XPathContext xctxt, int currentNode)
        throws javax.xml.transform.TransformerException
{

  DTM dtm = xctxt.getDTM(currentNode);

  if (dtm != null)
  {
    int expType = dtm.getExpandedTypeID(currentNode);

    return execute(xctxt, currentNode, dtm, expType);
  }

  return NodeTest.SCORE_NONE;
}
 

/**
 * Execute the function.  The function must return
 * a valid object.
 * @param xctxt The current execution context.
 * @return A valid XObject.
 *
 * @throws javax.xml.transform.TransformerException
 */
public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
{

  int which = getArg0AsNode(xctxt);

  if (DTM.NULL != which)
  {
    // Note that this is a different value than in previous releases
    // of Xalan. It's sensitive to the exact encoding of the node
    // handle anyway, so fighting to maintain backward compatability
    // really didn't make sense; it may change again as we continue
    // to experiment with balancing document and node numbers within
    // that value.
    return new XString("N" + Integer.toHexString(which).toUpperCase());
  }
  else
    return XString.EMPTYSTRING;
}
 

/**
 * Execute the first argument expression that is expected to return a
 * number.  If the argument is null, then get the number value from the
 * current context node.
 *
 * @param xctxt Runtime XPath context.
 *
 * @return The number value of the first argument, or the number value of the
 *         current context node if the first argument is null.
 *
 * @throws javax.xml.transform.TransformerException if an error occurs while
 *                                   executing the argument expression.
 */
protected double getArg0AsNumber(XPathContext xctxt)
        throws javax.xml.transform.TransformerException
{

  if(null == m_arg0)
  {
    int currentNode = xctxt.getCurrentNode();
    if(DTM.NULL == currentNode)
      return 0;
    else
    {
      DTM dtm = xctxt.getDTM(currentNode);
      XMLString str = dtm.getStringValue(currentNode);
      return str.toDouble();
    }
    
  }
  else
    return m_arg0.execute(xctxt).num();
}
 

/**
 * Construct a TransformerHandlerImpl.
 *
 * @param transformer Non-null reference to the Xalan transformer impl.
 * @param doFragment True if the result should be a document fragement.
 * @param baseSystemID  The system ID to use as the base for relative URLs.
 */
public TransformerHandlerImpl(TransformerImpl transformer,
                              boolean doFragment, String baseSystemID)
{

  super();

  m_transformer = transformer;
  m_baseSystemID = baseSystemID;

  XPathContext xctxt = transformer.getXPathContext();
  DTM dtm = xctxt.getDTM(null, true, transformer, true, true);
  
  m_dtm = dtm;
  dtm.setDocumentBaseURI(baseSystemID);

  m_contentHandler = dtm.getContentHandler();
  m_dtdHandler = dtm.getDTDHandler();
  m_entityResolver = dtm.getEntityResolver();
  m_errorHandler = dtm.getErrorHandler();
  m_lexicalHandler = dtm.getLexicalHandler();
  m_incremental = transformer.getIncremental();
  m_optimizer = transformer.getOptimize();
  m_source_location = transformer.getSource_location();
}
 

/**
 * Execute the first argument expression that is expected to return a
 * string.  If the argument is null, then get the string value from the
 * current context node.
 *
 * @param xctxt Runtime XPath context.
 *
 * @return The string value of the first argument, or the string value of the
 *         current context node if the first argument is null.
 *
 * @throws javax.xml.transform.TransformerException if an error occurs while
 *                                   executing the argument expression.
 */
protected XMLString getArg0AsString(XPathContext xctxt)
        throws javax.xml.transform.TransformerException
{
  if(null == m_arg0)
  {
    int currentNode = xctxt.getCurrentNode();
    if(DTM.NULL == currentNode)
      return XString.EMPTYSTRING;
    else
    {
      DTM dtm = xctxt.getDTM(currentNode);
      return dtm.getStringValue(currentNode);
    }
    
  }
  else
    return m_arg0.execute(xctxt).xstr();   
}
 

/**
 * Sort given nodes
 *
 *
 * @param xctxt The XPath runtime state for the sort.
 * @param keys Vector of sort keyx
 * @param sourceNodes Iterator of nodes to sort
 *
 * @return iterator of sorted nodes
 *
 * @throws TransformerException
 */
public DTMIterator sortNodes(
        XPathContext xctxt, Vector keys, DTMIterator sourceNodes)
          throws TransformerException
{

  NodeSorter sorter = new NodeSorter(xctxt);
  sourceNodes.setShouldCacheNodes(true);
  sourceNodes.runTo(-1);
  xctxt.pushContextNodeList(sourceNodes);

  try
  {
    sorter.sort(sourceNodes, keys, xctxt);
    sourceNodes.setCurrentPos(0);
  }
  finally
  {
    xctxt.popContextNodeList();
  }

  return sourceNodes;
}
 

/**
 * Return the value of the attribute interpreted as an Attribute
 * Value Template (in other words, you can use curly expressions
 * such as href="http://{website}".
 *
 * @param rawName Raw name of the attribute to get
 * @param sourceNode non-null reference to the <a href="http://www.w3.org/TR/xslt#dt-current-node">current source node</a>.
 * @param transformer non-null reference to the the current transform-time state.
 *
 * @return the value of the attribute
 *
 * @throws TransformerException
 */
public String getAttribute(
        String rawName, org.w3c.dom.Node sourceNode, TransformerImpl transformer)
          throws TransformerException
{

  AVT avt = getLiteralResultAttribute(rawName);

  if ((null != avt) && avt.getRawName().equals(rawName))
  {
    XPathContext xctxt = transformer.getXPathContext();

    return avt.evaluate(xctxt, 
          xctxt.getDTMHandleFromNode(sourceNode), 
          this);
  }

  return null;
}
 

/**
 * Construct a TransformerImpl.
 *
 * @param stylesheet The root of the stylesheet tree.
 */
public TransformerImpl(StylesheetRoot stylesheet)
 // throws javax.xml.transform.TransformerException    
{
  m_optimizer = stylesheet.getOptimizer();
  m_incremental = stylesheet.getIncremental();
  m_source_location = stylesheet.getSource_location();  	
  setStylesheet(stylesheet);
  XPathContext xPath = new XPathContext(this);
  xPath.setIncremental(m_incremental);
  xPath.getDTMManager().setIncremental(m_incremental);
  xPath.setSource_location(m_source_location);
  xPath.getDTMManager().setSource_location(m_source_location);
  
  if (stylesheet.isSecureProcessing())
    xPath.setSecureProcessing(true);
  
  setXPathContext(xPath);
  getXPathContext().setNamespaceContext(stylesheet);
}
 

/**
 * Get the target node that will be counted..
 *
 * @param xctxt The XPath runtime state for this.
 * @param sourceNode non-null reference to the <a href="http://www.w3.org/TR/xslt#dt-current-node">current source node</a>.
 *
 * @return the target node that will be counted
 *
 * @throws TransformerException
 */
public int getTargetNode(XPathContext xctxt, int sourceNode)
        throws TransformerException
{

  int target = DTM.NULL;
  XPath countMatchPattern = getCountMatchPattern(xctxt, sourceNode);

  if (Constants.NUMBERLEVEL_ANY == m_level)
  {
    target = findPrecedingOrAncestorOrSelf(xctxt, m_fromMatchPattern,
                                           countMatchPattern, sourceNode,
                                           this);
  }
  else
  {
    target = findAncestor(xctxt, m_fromMatchPattern, countMatchPattern,
                          sourceNode, this);
  }

  return target;
}
 

/**
 * Execute an expression in the XPath runtime context, and return the
 * result of the expression.
 *
 *
 * @param xctxt The XPath runtime context.
 * @param currentNode The currentNode.
 * @param dtm The DTM of the current node.
 * @param expType The expanded type ID of the current node.
 *
 * @return The result of the expression in the form of a <code>XObject</code>.
 *
 * @throws javax.xml.transform.TransformerException if a runtime exception
 *         occurs.
 */
public XObject execute(
        XPathContext xctxt, int currentNode, DTM dtm, int expType)
          throws javax.xml.transform.TransformerException
{

  if (m_whatToShow == NodeTest.SHOW_BYFUNCTION)
  {
    if (null != m_relativePathPattern)
    {
      return m_relativePathPattern.execute(xctxt);
    }
    else
      return NodeTest.SCORE_NONE;
  }

  XObject score;

  score = super.execute(xctxt, currentNode, dtm, expType);

  if (score == NodeTest.SCORE_NONE)
    return NodeTest.SCORE_NONE;

  if (getPredicateCount() != 0)
  {
    if (!executePredicates(xctxt, dtm, currentNode))
      return NodeTest.SCORE_NONE;
  }

  if (null != m_relativePathPattern)
    return m_relativePathPattern.executeRelativePathPattern(xctxt, dtm,
            currentNode);

  return score;
}
 

/**
 * OR two expressions and return the boolean result. Override
 * superclass method for optimization purposes.
 *
 * @param xctxt The runtime execution context.
 *
 * @return {@link org.apache.xpath.objects.XBoolean#S_TRUE} or 
 * {@link org.apache.xpath.objects.XBoolean#S_FALSE}.
 *
 * @throws javax.xml.transform.TransformerException
 */
public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
{

  XObject expr1 = m_left.execute(xctxt);

  if (!expr1.bool())
  {
    XObject expr2 = m_right.execute(xctxt);

    return expr2.bool() ? XBoolean.S_TRUE : XBoolean.S_FALSE;
  }
  else
    return XBoolean.S_TRUE;
}
 

/**
 * Execute a binary operation by calling execute on each of the operands,
 * and then calling the operate method on the derived class.
 *
 *
 * @param xctxt The runtime execution context.
 *
 * @return The XObject result of the operation.
 *
 * @throws javax.xml.transform.TransformerException
 */
public XObject execute(XPathContext xctxt)
        throws javax.xml.transform.TransformerException
{

  XObject left = m_left.execute(xctxt, true);
  XObject right = m_right.execute(xctxt, true);

  XObject result = operate(left, right);
  left.detach();
  right.detach();
  return result;
}
 

/**
 * Create an XRTreeFrag Object.
 *
 */
public XRTreeFrag(int root, XPathContext xctxt, ExpressionNode parent)
{
  super(null);
  exprSetParent(parent);
  initDTM(root, xctxt);    
}
 

/**
 * Given a result tree fragment, walk the tree and
 * output it to the SerializationHandler.
 *
 * @param obj Result tree fragment object
 * @param support XPath context for the result tree fragment
 *
 * @throws org.xml.sax.SAXException
 */
public static void outputResultTreeFragment(
    SerializationHandler handler,
    XObject obj,
    XPathContext support)
    throws org.xml.sax.SAXException
{

    int doc = obj.rtf();
    DTM dtm = support.getDTM(doc);

    if (null != dtm)
    {
        for (int n = dtm.getFirstChild(doc);
            DTM.NULL != n;
            n = dtm.getNextSibling(n))
        {
            handler.flushPending();

            // I think. . . . This used to have a (true) arg
            // to flush prefixes, will that cause problems ???
            if (dtm.getNodeType(n) == DTM.ELEMENT_NODE
                    && dtm.getNamespaceURI(n) == null)
                handler.startPrefixMapping("", "");
            dtm.dispatchToEvents(n, handler);
        }
    }
}
 

/**
  * Execute a binary operation by calling execute on each of the operands,
  * and then calling the operate method on the derived class.
  *
  *
  * @param xctxt The runtime execution context.
  *
  * @return The XObject result of the operation.
  *
  * @throws javax.xml.transform.TransformerException
  */
 public boolean bool(XPathContext xctxt)
         throws javax.xml.transform.TransformerException
 {
   XObject left = m_left.execute(xctxt, true);
   XObject right = m_right.execute(xctxt, true);

   boolean result = left.equals(right) ? true : false;
left.detach();
right.detach();
   return result;
 }
 

/**
 * Given a 'from' pattern (ala xsl:number), a match pattern
 * and a context, find the first ancestor that matches the
 * pattern (including the context handed in).
 *
 * @param xctxt The XPath runtime state for this.
 * @param fromMatchPattern The ancestor must match this pattern.
 * @param countMatchPattern The ancestor must also match this pattern.
 * @param context The node that "." expresses.
 * @param namespaceContext The context in which namespaces in the
 * queries are supposed to be expanded.
 *
 * @return the first ancestor that matches the given pattern
 *
 * @throws javax.xml.transform.TransformerException
 */
int findAncestor(
        XPathContext xctxt, XPath fromMatchPattern, XPath countMatchPattern, 
        int context, ElemNumber namespaceContext)
          throws javax.xml.transform.TransformerException
{
  DTM dtm = xctxt.getDTM(context);
  while (DTM.NULL != context)
  {
    if (null != fromMatchPattern)
    {
      if (fromMatchPattern.getMatchScore(xctxt, context)
              != XPath.MATCH_SCORE_NONE)
      {

        //context = null;
        break;
      }
    }

    if (null != countMatchPattern)
    {
      if (countMatchPattern.getMatchScore(xctxt, context)
              != XPath.MATCH_SCORE_NONE)
      {
        break;
      }
    }

    context = dtm.getParent(context);
  }

  return context;
}
 

/**
 * Execute the function.  The function must return
 * a valid object.
 * @param xctxt The current execution context.
 * @return A valid XObject.
 *
 * @throws javax.xml.transform.TransformerException
 */
public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
{

  int context = getArg0AsNode(xctxt);
  if(DTM.NULL == context)
    return XString.EMPTYSTRING;
  DTM dtm = xctxt.getDTM(context);
  String s = (context != DTM.NULL) ? dtm.getLocalName(context) : "";
  if(s.startsWith("#") || s.equals("xmlns"))
    return XString.EMPTYSTRING;

  return new XString(s);
}
 

/**
 * Try and find a node that was previously counted. If found,
 * return a positive integer that corresponds to the count.
 *
 * @param support The XPath context to use
 * @param node The node to be counted.
 * 
 * @return The count of the node, or -1 if not found.
 */
int getPreviouslyCounted(XPathContext support, int node)
{

  int n = m_countNodes.size();

  m_countResult = 0;

  for (int i = n - 1; i >= 0; i--)
  {
    int countedNode = m_countNodes.elementAt(i);

    if (node == countedNode)
    {

      // Since the list is in backwards order, the count is 
      // how many are in the rest of the list.
      m_countResult = i + 1 + m_countNodesStartCount;

      break;
    }
    
    DTM dtm = support.getDTM(countedNode);

    // Try to see if the given node falls after the counted node...
    // if it does, don't keep searching backwards.
    if (dtm.isNodeAfter(countedNode, node))
      break;
  }

  return m_countResult;
}
 

/**
 * Test a node to see if it matches any of the patterns in the union.
 *
 * @param xctxt XPath runtime context.
 *
 * @return {@link org.apache.xpath.patterns.NodeTest#SCORE_NODETEST},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_NONE},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_NSWILD},
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_QNAME}, or
 *         {@link org.apache.xpath.patterns.NodeTest#SCORE_OTHER}.
 *
 * @throws javax.xml.transform.TransformerException
 */
public XObject execute(XPathContext xctxt) throws javax.xml.transform.TransformerException
{

  XObject bestScore = null;
  int n = m_patterns.length;

  for (int i = 0; i < n; i++)
  {
    XObject score = m_patterns[i].execute(xctxt);

    if (score != NodeTest.SCORE_NONE)
    {
      if (null == bestScore)
        bestScore = score;
      else if (score.num() > bestScore.num())
        bestScore = score;
    }
  }

  if (null == bestScore)
  {
    bestScore = NodeTest.SCORE_NONE;
  }

  return bestScore;
}
 

/**
 * Tell the user of an error, and probably throw an
 * exception.
 *
 * @param xctxt The XPath runtime state.
 * @param msg The error message key
 * @param args Arguments to be used in the error message
 * @throws XSLProcessorException thrown if the active ProblemListener and XPathContext decide
 * the error condition is severe enough to halt processing.
 *
 * @throws javax.xml.transform.TransformerException
 */
public void error(XPathContext xctxt, String msg, Object args[])
        throws javax.xml.transform.TransformerException
{

  String formattedMsg = XSLMessages.createMessage(msg, args);
  ErrorListener errHandler = xctxt.getErrorListener();
  TransformerException spe = new TransformerException(formattedMsg,
                            (SourceLocator)xctxt.getSAXLocator());

  if (null != errHandler)
    errHandler.error(spe);
  else
    System.out.println(formattedMsg);
}
 

/**
 * Warn the user of a problem.
 *
 * @param xctxt The XPath runtime state.
 * @param msg Warning message key
 * @param args Arguments to be used in the warning message
 * @throws XSLProcessorException thrown if the active ProblemListener and XPathContext decide
 * the error condition is severe enough to halt processing.
 *
 * @throws javax.xml.transform.TransformerException
 */
public void warn(XPathContext xctxt, String msg, Object args[])
        throws javax.xml.transform.TransformerException
{

  String formattedMsg = XSLMessages.createWarning(msg, args);
  ErrorListener errHandler = xctxt.getErrorListener();
  TransformerException spe = new TransformerException(formattedMsg,
                            (SourceLocator)xctxt.getSAXLocator());

  if (null != errHandler)
    errHandler.warning(spe);
  else
    System.out.println(formattedMsg);
}
 

public XNodeSetForDOM(NodeIterator nodeIter, XPathContext xctxt)
{
  m_dtmMgr = xctxt.getDTMManager();
  m_origObj = nodeIter;

  // JKESS 20020514: Longer-term solution is to force
  // folks to request length through an accessor, so we can defer this
  // retrieval... but that requires an API change.
  // m_obj = new org.apache.xpath.NodeSetDTM(nodeIter, xctxt);
  org.apache.xpath.NodeSetDTM nsdtm=new org.apache.xpath.NodeSetDTM(nodeIter, xctxt);
  m_last=nsdtm.getLength();
  setObject(nsdtm);   
}
 

/**
 * Cast object to type t.
 *
 * @param t Type of object to cast this to
 * @param support XPath context to use for the conversion
 *
 * @return This object as the given type t
 *
 * @throws javax.xml.transform.TransformerException
 */
public Object castToType(int t, XPathContext support)
        throws javax.xml.transform.TransformerException
{

  Object result;

  switch (t)
  {
  case CLASS_STRING :
    result = str();
    break;
  case CLASS_NUMBER :
    result = new Double(num());
    break;
  case CLASS_NODESET :
    result = iter();
    break;
  case CLASS_BOOLEAN :
    result = new Boolean(bool());
    break;
  case CLASS_UNKNOWN :
    result = m_obj;
    break;

  // %TBD%  What to do here?
  //    case CLASS_RTREEFRAG :
  //      result = rtree(support);
  //      break;
  default :
    error(XPATHErrorResources.ER_CANT_CONVERT_TO_TYPE,
          new Object[]{ getTypeString(),
                        Integer.toString(t) });  //"Can not convert "+getTypeString()+" to a type#"+t);

    result = null;
  }

  return result;
}
 

public XNodeSetForDOM(NodeList nodeList, XPathContext xctxt)
{
  m_dtmMgr = xctxt.getDTMManager();
  m_origObj = nodeList;

  // JKESS 20020514: Longer-term solution is to force
  // folks to request length through an accessor, so we can defer this
  // retrieval... but that requires an API change.
  // m_obj=new org.apache.xpath.NodeSetDTM(nodeList, xctxt);
  org.apache.xpath.NodeSetDTM nsdtm=new org.apache.xpath.NodeSetDTM(nodeList, xctxt);
  m_last=nsdtm.getLength();
  setObject(nsdtm);   
}
 

/**
 * Conditionally execute a sub-template.
 * The expression is evaluated and the resulting object is converted
 * to a boolean as if by a call to the boolean function. If the result
 * is true, then the content template is instantiated; otherwise, nothing
 * is created.
 *
 * @param transformer non-null reference to the the current transform-time state.
 *
 * @throws TransformerException
 */
public void execute(TransformerImpl transformer) throws TransformerException
{

  XPathContext xctxt = transformer.getXPathContext();
  int sourceNode = xctxt.getCurrentNode();

    if (m_test.bool(xctxt, sourceNode, this)) {
        transformer.executeChildTemplates(this, true);
    }

}