Java example source code file (AxesWalker.java)

This example Java source code file (AxesWalker.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

axeswalker, cloneable, clonenotsupportedexception, dtm, dtmaxistraverser, error, expressionowner, object, pathcomponent, runtimeexception, setting, util, vector, walkingiterator, xpathcontext

The AxesWalker.java Java example source code

/*
 * reserved comment block
 * DO NOT REMOVE OR ALTER!
 */
/*
 * Copyright 1999-2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * $Id: AxesWalker.java,v 1.2.4.1 2005/09/14 19:45:22 jeffsuttor Exp $
 */
package com.sun.org.apache.xpath.internal.axes;

import java.util.Vector;

import com.sun.org.apache.xalan.internal.res.XSLMessages;
import com.sun.org.apache.xml.internal.dtm.DTM;
import com.sun.org.apache.xml.internal.dtm.DTMAxisTraverser;
import com.sun.org.apache.xml.internal.dtm.DTMIterator;
import com.sun.org.apache.xpath.internal.Expression;
import com.sun.org.apache.xpath.internal.ExpressionOwner;
import com.sun.org.apache.xpath.internal.XPathContext;
import com.sun.org.apache.xpath.internal.XPathVisitor;
import com.sun.org.apache.xpath.internal.compiler.Compiler;
import com.sun.org.apache.xpath.internal.res.XPATHErrorResources;

/**
 * Serves as common interface for axes Walkers, and stores common
 * state variables.
 */
public class AxesWalker extends PredicatedNodeTest
        implements Cloneable, PathComponent, ExpressionOwner
{
    static final long serialVersionUID = -2966031951306601247L;

  /**
   * 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_traverser = 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;
  }

  /**
   * Set or clear the previous walker reference in the location step chain.
   *
   *
   * @param walker Reference to previous walker reference in the location
   *               step chain, or null.
   */
  public void setPrevWalker(AxesWalker walker)
  {
    m_prevWalker = walker;
  }

  /**
   * Get the previous walker reference in the location step chain.
   *
   *
   * @return Reference to previous walker reference in the location
   *               step chain, or null.
   */
  public AxesWalker getPrevWalker()
  {
    return m_prevWalker;
  }

  /**
   * This is simply a way to bottle-neck the return of the next node, for
   * diagnostic purposes.
   *
   * @param n Node to return, or null.
   *
   * @return The argument.
   */
  private int returnNextNode(int n)
  {

    return n;
  }

  /**
   * Get the next node in document order on the axes.
   *
   * @return the next node in document order on the axes, or null.
   */
  protected int getNextNode()
  {
    if (m_foundLast)
      return DTM.NULL;

    if (m_isFresh)
    {
      m_currentNode = m_traverser.first(m_root);
      m_isFresh = false;
    }
    // I shouldn't have to do this the check for current node, I think.
    // numbering\numbering24.xsl fails if I don't do this.  I think
    // it occurs as the walkers are backing up. -sb
    else if(DTM.NULL != m_currentNode)
    {
      m_currentNode = m_traverser.next(m_root, m_currentNode);
    }

    if (DTM.NULL == m_currentNode)
      this.m_foundLast = true;

    return m_currentNode;
  }

  /**
   *  Moves the <code>TreeWalker to the next visible node in document
   * order relative to the current node, and returns the new node. If the
   * current node has no next node,  or if the search for nextNode attempts
   * to step upward from the TreeWalker's root node, returns
   * <code>null , and retains the current node.
   * @return  The new node, or <code>null if the current node has no
   *   next node  in the TreeWalker's logical view.
   */
  public int nextNode()
  {
    int nextNode = DTM.NULL;
    AxesWalker walker = wi().getLastUsedWalker();

    while (true)
    {
      if (null == walker)
        break;

      nextNode = walker.getNextNode();

      if (DTM.NULL == nextNode)
      {

        walker = walker.m_prevWalker;
      }
      else
      {
        if (walker.acceptNode(nextNode) != DTMIterator.FILTER_ACCEPT)
        {
          continue;
        }

        if (null == walker.m_nextWalker)
        {
          wi().setLastUsedWalker(walker);

          // return walker.returnNextNode(nextNode);
          break;
        }
        else
        {
          AxesWalker prev = walker;

          walker = walker.m_nextWalker;

          walker.setRoot(nextNode);

          walker.m_prevWalker = prev;

          continue;
        }
      }  // if(null != nextNode)
    }  // while(null != walker)

    return nextNode;
  }

  //============= End TreeWalker Implementation =============

  /**
   * Get the index of the last node that can be itterated to.
   *
   *
   * @param xctxt XPath runtime context.
   *
   * @return the index of the last node that can be itterated to.
   */
  public int getLastPos(XPathContext xctxt)
  {

    int pos = getProximityPosition();

    AxesWalker walker;

    try
    {
      walker = (AxesWalker) clone();
    }
    catch (CloneNotSupportedException cnse)
    {
      return -1;
    }

    walker.setPredicateCount(m_predicateIndex);
    walker.setNextWalker(null);
    walker.setPrevWalker(null);

    WalkingIterator lpi = wi();
    AxesWalker savedWalker = lpi.getLastUsedWalker();

    try
    {
      lpi.setLastUsedWalker(walker);

      int next;

      while (DTM.NULL != (next = walker.nextNode()))
      {
        pos++;
      }

      // TODO: Should probably save this in the iterator.
    }
    finally
    {
      lpi.setLastUsedWalker(savedWalker);
    }

    // System.out.println("pos: "+pos);
    return pos;
  }

  //============= State Data =============

  /**
   * The DTM for the root.  This can not be used, or must be changed,
   * for the filter walker, or any walker that can have nodes
   * from multiple documents.
   * Never, ever, access this value without going through getDTM(int node).
   */
  private DTM m_dtm;

  /**
   * Set the DTM for this walker.
   *
   * @param dtm Non-null reference to a DTM.
   */
  public void setDefaultDTM(DTM dtm)
  {
    m_dtm = dtm;
  }

  /**
   * Get the DTM for this walker.
   *
   * @return Non-null reference to a DTM.
   */
  public DTM getDTM(int node)
  {
    //
    return wi().getXPathContext().getDTM(node);
  }

  /**
   * Returns true if all the nodes in the iteration well be returned in document
   * order.
   * Warning: This can only be called after setRoot has been called!
   *
   * @return true as a default.
   */
  public boolean isDocOrdered()
  {
    return true;
  }

  /**
   * Returns the axis being iterated, if it is known.
   *
   * @return Axis.CHILD, etc., or -1 if the axis is not known or is of multiple
   * types.
   */
  public int getAxis()
  {
    return m_axis;
  }

  /**
   * This will traverse the heararchy, calling the visitor for
   * each member.  If the called visitor method returns
   * false, the subtree should not be called.
   *
   * @param owner The owner of the visitor, where that path may be
   *              rewritten if needed.
   * @param visitor The visitor whose appropriate method will be called.
   */
  public void callVisitors(ExpressionOwner owner, XPathVisitor visitor)
  {
        if(visitor.visitStep(owner, this))
        {
                callPredicateVisitors(visitor);
                if(null != m_nextWalker)
                {
                        m_nextWalker.callVisitors(this, visitor);
                }
        }
  }

  /**
   * @see ExpressionOwner#getExpression()
   */
  public Expression getExpression()
  {
    return m_nextWalker;
  }

  /**
   * @see ExpressionOwner#setExpression(Expression)
   */
  public void setExpression(Expression exp)
  {
        exp.exprSetParent(this);
        m_nextWalker = (AxesWalker)exp;
  }

    /**
     * @see Expression#deepEquals(Expression)
     */
    public boolean deepEquals(Expression expr)
    {
      if (!super.deepEquals(expr))
                return false;

      AxesWalker walker = (AxesWalker)expr;
      if(this.m_axis != walker.m_axis)
        return false;

      return true;
    }

  /**
   *  The root node of the TreeWalker, as specified when it was created.
   */
  transient int m_root = DTM.NULL;

  /**
   *  The node at which the TreeWalker is currently positioned.
   */
  private transient int m_currentNode = DTM.NULL;

  /** True if an itteration has not begun.  */
  transient boolean m_isFresh;

  /** The next walker in the location step chain.
   *  @serial  */
  protected AxesWalker m_nextWalker;

  /** The previous walker in the location step chain, or null.
   *  @serial   */
  AxesWalker m_prevWalker;

  /** The traversal axis from where the nodes will be filtered. */
  protected int m_axis = -1;

  /** The DTM inner traversal class, that corresponds to the super axis. */
  protected DTMAxisTraverser m_traverser;
}