axeswalker.java

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/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:  
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Xalan" and "Apache Software Foundation" must
 *    not be used to endorse or promote products derived from this
 *    software without prior written permission. For written 
 *    permission, please contact [e-mail].
 *
 * 5. Products derived from this software may not be called "Apache",
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 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xpath.axes;

import java.util.Vector;

import javax.xml.transform.TransformerException;
import org.apache.xml.dtm.DTM;
import org.apache.xml.dtm.DTMAxisTraverser;
import org.apache.xml.dtm.DTMIterator;
import org.apache.xpath.Expression;
import org.apache.xpath.ExpressionOwner;
import org.apache.xpath.XPathContext;
import org.apache.xpath.XPathVisitor;
import org.apache.xpath.compiler.Compiler;
import org.apache.xpath.patterns.NodeTest;

import org.apache.xpath.res.XPATHErrorResources;
import org.apache.xalan.res.XSLMessages;

/**
 * Serves as common interface for axes Walkers, and stores common
 * state variables.
 */
public class AxesWalker extends PredicatedNodeTest
        implements Cloneable, PathComponent, ExpressionOwner
{
  
  /**
   * Construct an AxesWalker using a LocPathIterator.
   *
   * @param locPathIterator non-null reference to the parent iterator.
   */
  public AxesWalker(LocPathIterator locPathIterator, int axis)
  {
    super( locPathIterator );
    m_axis = axis;
  }
  
  public final WalkingIterator wi()
  {
    return (WalkingIterator)m_lpi;
  }

  /**
   * Initialize an AxesWalker during the parse of the XPath expression.
   *
   * @param compiler The Compiler object that has information about this 
   *                 walker in the op map.
   * @param opPos The op code position of this location step.
   * @param stepType  The type of location step.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public void init(Compiler compiler, int opPos, int stepType)
          throws javax.xml.transform.TransformerException
  {

    initPredicateInfo(compiler, opPos);

    // int testType = compiler.getOp(nodeTestOpPos);
  }

  /**
   * Get a cloned AxesWalker.
   *
   * @return A new AxesWalker that can be used without mutating this one.
   *
   * @throws CloneNotSupportedException
   */
  public Object clone() throws CloneNotSupportedException
  {
    // Do not access the location path itterator during this operation!
    
    AxesWalker clone = (AxesWalker) super.clone();

    //clone.setCurrentNode(clone.m_root);

    // clone.m_isFresh = true;

    return clone;
  }
  
  /**
   * Do a deep clone of this walker, including next and previous walkers.
   * If the this AxesWalker is on the clone list, don't clone but 
   * return the already cloned version.
   * 
   * @param cloneOwner non-null reference to the cloned location path 
   *                   iterator to which this clone will be added.
   * @param cloneList non-null vector of sources in odd elements, and the 
   *                  corresponding clones in even vectors.
   * 
   * @return non-null clone, which may be a new clone, or may be a clone 
   *         contained on the cloneList.
   */
  AxesWalker cloneDeep(WalkingIterator cloneOwner, Vector cloneList)
     throws CloneNotSupportedException
  {
    AxesWalker clone = findClone(this, cloneList);
    if(null != clone)
      return clone;
    clone = (AxesWalker)this.clone();
    clone.setLocPathIterator(cloneOwner);
    if(null != cloneList)
    {
      cloneList.addElement(this);
      cloneList.addElement(clone);
    }
    
    if(wi().m_lastUsedWalker == this)
      cloneOwner.m_lastUsedWalker = clone;
      
    if(null != m_nextWalker)
      clone.m_nextWalker = m_nextWalker.cloneDeep(cloneOwner, cloneList);
      
    // If you don't check for the cloneList here, you'll go into an 
    // recursive infinate loop.  
    if(null != cloneList)
    {
      if(null != m_prevWalker)
        clone.m_prevWalker = m_prevWalker.cloneDeep(cloneOwner, cloneList);
    }
    else
    {
      if(null != m_nextWalker)
        clone.m_nextWalker.m_prevWalker = clone;
    }
    return clone;
  }
  
  /**
   * Find a clone that corresponds to the key argument.
   * 
   * @param key The original AxesWalker for which there may be a clone.
   * @param cloneList vector of sources in odd elements, and the 
   *                  corresponding clones in even vectors, may be null.
   * 
   * @return A clone that corresponds to the key, or null if key not found.
   */
  static AxesWalker findClone(AxesWalker key, Vector cloneList)
  {
    if(null != cloneList)
    {
      // First, look for clone on list.
      int n = cloneList.size();
      for (int i = 0; i < n; i+=2) 
      {
        if(key == cloneList.elementAt(i))
          return (AxesWalker)cloneList.elementAt(i+1);
      }
    }
    return null;    
  }
  
  /**
   * Detaches the walker from the set which it iterated over, releasing
   * any computational resources and placing the iterator in the INVALID
   * state.
   */
  public void detach()
  { 
  	m_currentNode = DTM.NULL;
  	m_dtm = null;
  	m_isFresh = true;
  	m_root = DTM.NULL;
  }
  
  //=============== TreeWalker Implementation ===============

  /**
   * The root node of the TreeWalker, as specified in setRoot(int root).
   * Note that this may actually be below the current node.
   *
   * @return The context node of the step.
   */
  public int getRoot()
  {
    return m_root;
  }
  
  /** 
   * Get the analysis bits for this walker, as defined in the WalkerFactory.
   * @return One of WalkerFactory#BIT_DESCENDANT, etc.
   */
  public int getAnalysisBits()
  {
  	int axis = getAxis();
  	int bit = WalkerFactory.getAnalysisBitFromAxes(axis);
  	return bit;
  }

  /**
   * Set the root node of the TreeWalker.
   * (Not part of the DOM2 TreeWalker interface).
   *
   * @param root The context node of this step.
   */
  public void setRoot(int root)
  {
    // %OPT% Get this directly from the lpi.
    XPathContext xctxt = wi().getXPathContext();
    m_dtm = xctxt.getDTM(root);
    m_traverser = m_dtm.getAxisTraverser(m_axis);
    m_isFresh = true;
    m_foundLast = false;
    m_root = root;
    m_currentNode = root;

    if (DTM.NULL == root)
    {
      throw new RuntimeException(
        XSLMessages.createXPATHMessage(XPATHErrorResources.ER_SETTING_WALKER_ROOT_TO_NULL, null)); //"\n !!!! Error! Setting the root of a walker to null!!!");
    }

    resetProximityPositions();
  }

  /**
   * The node at which the TreeWalker is currently positioned.
   * <br> The value must not be null. Alterations to the DOM tree may cause
   * the current node to no longer be accepted by the TreeWalker's
   * associated filter. currentNode may also be explicitly set to any node,
   * whether or not it is within the subtree specified by the root node or
   * would be accepted by the filter and whatToShow flags. Further
   * traversal occurs relative to currentNode even if it is not part of the
   * current view by applying the filters in the requested direction (not
   * changing currentNode where no traversal is possible).
   *
   * @return The node at which the TreeWalker is currently positioned, only null 
   * if setRoot has not yet been called.
   */
  public final int getCurrentNode()
  {
    return m_currentNode;
  }

  /**
   * Set the next walker in the location step chain.
   *
   *
   * @param walker Reference to AxesWalker derivative, or may be null.
   */
  public void setNextWalker(AxesWalker walker)
  {
    m_nextWalker = walker;
  }

  /**
   * Get the next walker in the location step chain.
   *
   *
   * @return Reference to AxesWalker derivative, or null.
   */
  public AxesWalker getNextWalker()
  {
    return m_nextWalker;
  }

  /**