unionpathiterator.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].
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 * 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,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * 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/>.
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package org.apache.xpath.axes;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;
import java.util.Vector;

import javax.xml.transform.TransformerException;
import org.apache.xml.dtm.Axis;
import org.apache.xml.dtm.DTM;
import org.apache.xml.dtm.DTMIterator;
import org.apache.xpath.Expression;
import org.apache.xpath.ExpressionOwner;
import org.apache.xpath.XPathVisitor;
import org.apache.xpath.compiler.Compiler;
import org.apache.xpath.compiler.OpCodes;

/**
 * <meta name="usage" content="advanced"/>
 * This class extends NodeSetDTM, which implements DTMIterator,
 * and fetches nodes one at a time in document order based on a XPath
 * <a href="http://www.w3.org/TR/xpath#NT-UnionExpr">UnionExpr</a>.
 * As each node is iterated via nextNode(), the node is also stored
 * in the NodeVector, so that previousNode() can easily be done.
 */
public class UnionPathIterator extends LocPathIterator
        implements Cloneable, DTMIterator, java.io.Serializable, PathComponent
{

  /**
   * Constructor to create an instance which you can add location paths to.
   */
  public UnionPathIterator()
  {

    super();

    // m_mutable = false;
    // m_cacheNodes = false;
    m_iterators = null;
    m_exprs = null;
  }

  /**
   * Initialize the context values for this expression 
   * after it is cloned.
   *
   * @param execContext The XPath runtime context for this 
   * transformation.
   */
  public void setRoot(int context, Object environment)
  {
    super.setRoot(context, environment);

    try
    {
      if (null != m_exprs)
      {
        int n = m_exprs.length;
        DTMIterator newIters[] = new DTMIterator[n];
  
        for (int i = 0; i < n; i++)
        {
          DTMIterator iter = m_exprs[i].asIterator(m_execContext, context);
          newIters[i] = iter;
          iter.nextNode();
        }
        m_iterators = newIters;
      }
    }
    catch(Exception e)
    {
      throw new org.apache.xml.utils.WrappedRuntimeException(e);
    }
  }
  
  /**
   * Add an iterator to the union list.
   *
   * @param iter non-null reference to a location path iterator.
   */
  public void addIterator(DTMIterator expr)
  {

    // Increase array size by only 1 at a time.  Fix this
    // if it looks to be a problem.
    if (null == m_iterators)
    {
      m_iterators = new DTMIterator[1];
      m_iterators[0] = expr;
    }
    else
    {
      DTMIterator[] exprs = m_iterators;
      int len = m_iterators.length;

      m_iterators = new DTMIterator[len + 1];

      System.arraycopy(exprs, 0, m_iterators, 0, len);

      m_iterators[len] = expr;
    }
    expr.nextNode();
    if(expr instanceof Expression)
    	((Expression)expr).exprSetParent(this);
  }
  
  /**
   *  Detaches the iterator from the set which it iterated over, releasing
   * any computational resources and placing the iterator in the INVALID
   * state. After<code>detach</code> has been invoked, calls to
   * <code>nextNode</code> or<code>previousNode</code> will raise the
   * exception INVALID_STATE_ERR.
   */
  public void detach()
  {    
    if(null != m_iterators)
    {
    	int n = m_iterators.length;
    	for(int i = 0; i < n; i++)
    	{
    		m_iterators[i].detach();
    	}
    	m_iterators = null;
    }
  }


  /**
   * Create a UnionPathIterator object, including creation 
   * of location path iterators from the opcode list, and call back 
   * into the Compiler to create predicate expressions.
   *
   * @param compiler The Compiler which is creating 
   * this expression.
   * @param opPos The position of this iterator in the 
   * opcode list from the compiler.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public UnionPathIterator(Compiler compiler, int opPos)
          throws javax.xml.transform.TransformerException
  {

    super();

    opPos = compiler.getFirstChildPos(opPos);

    loadLocationPaths(compiler, opPos, 0);
  }
  
  /**
   * This will return an iterator capable of handling the union of paths given.
   * 
   * @param compiler The Compiler which is creating 
   * this expression.
   * @param opPos The position of this iterator in the 
   * opcode list from the compiler.
   * 
   * @return Object that is derived from LocPathIterator.
   *
   * @throws javax.xml.transform.TransformerException
   */
  public static LocPathIterator createUnionIterator(Compiler compiler, int opPos)
          throws javax.xml.transform.TransformerException
  {
  	// For the moment, I'm going to first create a full UnionPathIterator, and 
  	// then see if I can reduce it to a UnionChildIterator.  It would obviously 
  	// be more effecient to just test for the conditions for a UnionChildIterator, 
  	// and then create that directly.
  	UnionPathIterator upi = new UnionPathIterator(compiler, opPos);
  	int nPaths = upi.m_exprs.length;
  	boolean isAllChildIterators = true;
  	for(int i = 0; i < nPaths; i++)
  	{
  		LocPathIterator lpi = upi.m_exprs[i];
  		
  		if(lpi.getAxis() != Axis.CHILD)
  		{
  			isAllChildIterators = false;
  			break;
  		}
  		else
  		{
  			// check for positional predicates or position function, which won't work.
  			if(HasPositionalPredChecker.check(lpi))
  			{
  				isAllChildIterators = false;
  				break;
  			}
  		}
  	}
  	if(isAllChildIterators)
  	{
  		UnionChildIterator uci = new UnionChildIterator();
  		
	  	for(int i = 0; i < nPaths; i++)
	  	{
	  		PredicatedNodeTest lpi = upi.m_exprs[i];
	  		// I could strip the lpi down to a pure PredicatedNodeTest, but 
	  		// I don't think it's worth it.  Note that the test can be used 
	  		// as a static object... so it doesn't have to be cloned.
	  		uci.addNodeTest(lpi);
	  	}
	  	return uci;
  		
  	}
  	else
  		return upi;
  }
  
  /** 
   * Get the analysis bits for this walker, as defined in the WalkerFactory.
   * @return One of WalkerFactory#BIT_DESCENDANT, etc.
   */
  public int getAnalysisBits()
  {
    int bits = 0;
    
    if (m_exprs != null)
    {
      int n = m_exprs.length;

      for (int i = 0; i < n; i++)
      {
      	int bit = m_exprs[i].getAnalysisBits();
        bits |= bit;
      }
    }

    return bits;
  }
  
  /**
   * Read the object from a serialization stream.
   *
   * @param stream Input stream to read from
   *
   * @throws java.io.IOException
   * @throws javax.xml.transform.TransformerException
   */
  private void readObject(java.io.ObjectInputStream stream)
          throws java.io.IOException, javax.xml.transform.TransformerException
  {
    try
    {
      stream.defaultReadObject();
      m_clones =  new IteratorPool(this);
    }
    catch (ClassNotFoundException cnfe)
    {
      throw new javax.xml.transform.TransformerException(cnfe);
    }
  }

  /**
   * Get a cloned LocPathIterator that holds the same