AxesWalker


1   /*
2    * Copyright 1999-2004 The Apache Software Foundation.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *     http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  /*
17   * $Id: AxesWalker.java,v 1.28 2004/02/17 04:32:08 minchau Exp $
18   */
19  package org.apache.xpath.axes;
20  
21  import java.util.Vector  ;
22  
23  import org.apache.xalan.res.XSLMessages;
24  import org.apache.xml.dtm.DTM;
25  import org.apache.xml.dtm.DTMAxisTraverser;
26  import org.apache.xml.dtm.DTMIterator;
27  import org.apache.xpath.Expression;
28  import org.apache.xpath.ExpressionOwner;
29  import org.apache.xpath.XPathContext;
30  import org.apache.xpath.XPathVisitor;
31  import org.apache.xpath.compiler.Compiler;
32  import org.apache.xpath.res.XPATHErrorResources;
33  
34  /**
35   * Serves as common interface for axes Walkers, and stores common
36   * state variables.
37   */
38  public class AxesWalker extends PredicatedNodeTest
39          implements Cloneable  , PathComponent, ExpressionOwner
40  {
41    
42    /**
43     * Construct an AxesWalker using a LocPathIterator.
44     *
45     * @param locPathIterator non-null reference to the parent iterator.
46     */
47    public AxesWalker(LocPathIterator locPathIterator, int axis)
48    {
49      super( locPathIterator );
50      m_axis = axis;
51    }
52    
53    public final WalkingIterator wi()
54    {
55      return (WalkingIterator)m_lpi;
56    }
57  
58    /**
59     * Initialize an AxesWalker during the parse of the XPath expression.
60     *
61     * @param compiler The Compiler object that has information about this 
62     *                 walker in the op map.
63     * @param opPos The op code position of this location step.
64     * @param stepType  The type of location step.
65     *
66     * @throws javax.xml.transform.TransformerException
67     */
68    public void init(Compiler   compiler, int opPos, int stepType)
69            throws javax.xml.transform.TransformerException  
70    {
71  
72      initPredicateInfo(compiler, opPos);
73  
74      // int testType = compiler.getOp(nodeTestOpPos);
75    }
76  
77    /**
78     * Get a cloned AxesWalker.
79     *
80     * @return A new AxesWalker that can be used without mutating this one.
81     *
82     * @throws CloneNotSupportedException
83     */
84    public Object   clone() throws CloneNotSupportedException  
85    {
86      // Do not access the location path itterator during this operation!
87      
88      AxesWalker clone = (AxesWalker) super.clone();
89  
90      //clone.setCurrentNode(clone.m_root);
91  
92      // clone.m_isFresh = true;
93  
94      return clone;
95    }
96    
97    /**
98     * Do a deep clone of this walker, including next and previous walkers.
99     * If the this AxesWalker is on the clone list, don't clone but 
100    * return the already cloned version.
101    * 
102    * @param cloneOwner non-null reference to the cloned location path 
103    *                   iterator to which this clone will be added.
104    * @param cloneList non-null vector of sources in odd elements, and the 
105    *                  corresponding clones in even vectors.
106    * 
107    * @return non-null clone, which may be a new clone, or may be a clone 
108    *         contained on the cloneList.
109    */
110   AxesWalker cloneDeep(WalkingIterator cloneOwner, Vector   cloneList)
111      throws CloneNotSupportedException  
112   {
113     AxesWalker clone = findClone(this, cloneList);
114     if(null != clone)
115       return clone;
116     clone = (AxesWalker)this.clone();
117     clone.setLocPathIterator(cloneOwner);
118     if(null != cloneList)
119     {
120       cloneList.addElement(this);
121       cloneList.addElement(clone);
122     }
123     
124     if(wi().m_lastUsedWalker == this)
125       cloneOwner.m_lastUsedWalker = clone;
126       
127     if(null != m_nextWalker)
128       clone.m_nextWalker = m_nextWalker.cloneDeep(cloneOwner, cloneList);
129       
130     // If you don't check for the cloneList here, you'll go into an 
131     // recursive infinate loop.  
132     if(null != cloneList)
133     {
134       if(null != m_prevWalker)
135         clone.m_prevWalker = m_prevWalker.cloneDeep(cloneOwner, cloneList);
136     }
137     else
138     {
139       if(null != m_nextWalker)
140         clone.m_nextWalker.m_prevWalker = clone;
141     }
142     return clone;
143   }
144   
145   /**
146    * Find a clone that corresponds to the key argument.
147    * 
148    * @param key The original AxesWalker for which there may be a clone.
149    * @param cloneList vector of sources in odd elements, and the 
150    *                  corresponding clones in even vectors, may be null.
151    * 
152    * @return A clone that corresponds to the key, or null if key not found.
153    */
154   static AxesWalker findClone(AxesWalker key, Vector   cloneList)
155   {
156     if(null != cloneList)
157     {
158       // First, look for clone on list.
159       int n = cloneList.size();
160       for (int i = 0; i < n; i+=2) 
161       {
162         if(key == cloneList.elementAt(i))
163           return (AxesWalker)cloneList.elementAt(i+1);
164       }
165     }
166     return null;    
167   }
168   
169   /**
170    * Detaches the walker from the set which it iterated over, releasing
171    * any computational resources and placing the iterator in the INVALID
172    * state.
173    */
174   public void detach()
175   { 
176     m_currentNode = DTM.NULL;
177     m_dtm = null;
178     m_traverser = null;
179     m_isFresh = true;
180     m_root = DTM.NULL;
181   }
182   
183   //=============== TreeWalker Implementation ===============
184 
185   /**
186    * The root node of the TreeWalker, as specified in setRoot(int root).
187    * Note that this may actually be below the current node.
188    *
189    * @return The context node of the step.
190    */
191   public int getRoot()
192   {
193     return m_root;
194   }
195   
196   /** 
197    * Get the analysis bits for this walker, as defined in the WalkerFactory.
198    * @return One of WalkerFactory#BIT_DESCENDANT, etc.
199    */
200   public int getAnalysisBits()
201   {
202     int axis = getAxis();
203     int bit = WalkerFactory.getAnalysisBitFromAxes(axis);
204     return bit;
205   }
206 
207   /**
208    * Set the root node of the TreeWalker.
209    * (Not part of the DOM2 TreeWalker interface).
210    *
211    * @param root The context node of this step.
212    */
213   public void setRoot(int root)
214   {
215     // %OPT% Get this directly from the lpi.
216     XPathContext xctxt = wi().getXPathContext();
217     m_dtm = xctxt.getDTM(root);
218     m_traverser = m_dtm.getAxisTraverser(m_axis);
219     m_isFresh = true;
220     m_foundLast = false;
221     m_root = root;
222     m_currentNode = root;
223 
224     if (DTM.NULL == root)
225     {
226       throw new RuntimeException  (
227         XSLMessages.createXPATHMessage(XPATHErrorResources.ER_SETTING_WALKER_ROOT_TO_NULL, null)); //"\n !!!! Error! Setting the root of a walker to null!!!");
228     }
229 
230     resetProximityPositions();
231   }
232 
233   /**
234    * The node at which the TreeWalker is currently positioned.
235    * <br> The value must not be null. Alterations to the DOM tree may cause
236    * the current node to no longer be accepted by the TreeWalker's
237    * associated filter. currentNode may also be explicitly set to any node,
238    * whether or not it is within the subtree specified by the root node or
239    * would be accepted by the filter and whatToShow flags. Further
240    * traversal occurs relative to currentNode even if it is not part of the
241    * current view by applying the filters in the requested direction (not
242    * changing currentNode where no traversal is possible).
243    *
244    * @return The node at which the TreeWalker is currently positioned, only null 
245    * if setRoot has not yet been called.
246    */
247   public final int getCurrentNode()
248   {
249     return m_currentNode;
250   }
251 
252   /**
253    * Set the next walker in the location step chain.
254    *
255    *
256    * @param walker Reference to AxesWalker derivative, or may be null.
257    */
258   public void setNextWalker(AxesWalker walker)
259   {
260     m_nextWalker = walker;
261   }
262 
263   /**
264    * Get the next walker in the location step chain.
265    *
266    *
267    * @return Reference to AxesWalker derivative, or null.
268    */
269   public AxesWalker getNextWalker()
270   {
271     return m_nextWalker;
272   }
273 
274   /**
275    * Set or clear the previous walker reference in the location step chain.
276    *
277    *
278    * @param walker Reference to previous walker reference in the location 
279    *               step chain, or null.
280    */
281   public void setPrevWalker(AxesWalker walker)
282   {
283     m_prevWalker = walker;
284   }
285 
286   /**
287    * Get the previous walker reference in the location step chain.
288    *
289    *
290    * @return Reference to previous walker reference in the location 
291    *               step chain, or null.
292    */
293   public AxesWalker getPrevWalker()
294   {
295     return m_prevWalker;
296   }
297 
298   /**
299    * This is simply a way to bottle-neck the return of the next node, for 
300    * diagnostic purposes.
301    *
302    * @param n Node to return, or null.
303    *
304    * @return The argument.
305    */
306   private int returnNextNode(int n)
307   {
308 
309     return n;
310   }
311 
312   /**
313    * Get the next node in document order on the axes.
314    *
315    * @return the next node in document order on the axes, or null.
316    */
317   protected int getNextNode()
318   {
319     if (m_foundLast)
320       return DTM.NULL;
321 
322     if (m_isFresh)
323     {
324       m_currentNode = m_traverser.first(m_root);
325       m_isFresh = false;
326     }
327     // I shouldn't have to do this the check for current node, I think.
328     // numbering\numbering24.xsl fails if I don't do this.  I think 
329     // it occurs as the walkers are backing up. -sb
330     else if(DTM.NULL != m_currentNode) 
331     {
332       m_currentNode = m_traverser.next(m_root, m_currentNode);
333     }
334 
335     if (DTM.NULL == m_currentNode)
336       this.m_foundLast = true;
337 
338     return m_currentNode;
339   }
340 
341   /**
342    *  Moves the <code>TreeWalker</code> to the next visible node in document
343    * order relative to the current node, and returns the new node. If the
344    * current node has no next node,  or if the search for nextNode attempts
345    * to step upward from the TreeWalker's root node, returns
346    * <code>null</code> , and retains the current node.
347    * @return  The new node, or <code>null</code> if the current node has no
348    *   next node  in the TreeWalker's logical view.
349    */
350   public int nextNode()
351   {
352     int nextNode = DTM.NULL;
353     AxesWalker walker = wi().getLastUsedWalker();
354 
355     while (true)
356     {
357       if (null == walker)
358         break;
359 
360       nextNode = walker.getNextNode();
361 
362       if (DTM.NULL == nextNode)
363       {
364 
365         walker = walker.m_prevWalker;
366       }
367       else
368       {
369         if (walker.acceptNode(nextNode) != DTMIterator.FILTER_ACCEPT)
370         {
371           continue;
372         }
373 
374         if (null == walker.m_nextWalker)
375         {
376           wi().setLastUsedWalker(walker);
377 
378           // return walker.returnNextNode(nextNode);
379           break;
380         }
381         else
382         {
383           AxesWalker prev = walker;
384 
385           walker = walker.m_nextWalker;
386 
387           walker.setRoot(nextNode);
388 
389           walker.m_prevWalker = prev;
390 
391           continue;
392         }
393       }  // if(null != nextNode)
394     }  // while(null != walker)
395 
396     return nextNode;
397   }
398 
399   //============= End TreeWalker Implementation =============
400 
401   /**
402    * Get the index of the last node that can be itterated to.
403    *
404    *
405    * @param xctxt XPath runtime context.
406    *
407    * @return the index of the last node that can be itterated to.
408    */
409   public int getLastPos(XPathContext xctxt)
410   {
411 
412     int pos = getProximityPosition();
413     
414     AxesWalker walker;
415 
416     try
417     {
418       walker = (AxesWalker) clone();
419     }
420     catch (CloneNotSupportedException   cnse)
421     {
422       return -1;
423     }
424 
425     walker.setPredicateCount(walker.getPredicateCount() - 1);
426     walker.setNextWalker(null);
427     walker.setPrevWalker(null);
428 
429     WalkingIterator lpi = wi();
430     AxesWalker savedWalker = lpi.getLastUsedWalker();
431 
432     try
433     {
434       lpi.setLastUsedWalker(walker);
435 
436       int next;
437 
438       while (DTM.NULL != (next = walker.nextNode()))
439       {
440         pos++;
441       }
442 
443       // TODO: Should probably save this in the iterator.
444     }
445     finally
446     {
447       lpi.setLastUsedWalker(savedWalker);
448     }
449 
450     // System.out.println("pos: "+pos);
451     return pos;
452   }
453   
454   //============= State Data =============
455   
456   /**
457    * The DTM for the root.  This can not be used, or must be changed, 
458    * for the filter walker, or any walker that can have nodes 
459    * from multiple documents.
460    * Never, ever, access this value without going through getDTM(int node).
461    */
462   private DTM m_dtm;
463   
464   /**
465    * Set the DTM for this walker.
466    * 
467    * @param dtm Non-null reference to a DTM.
468    */
469   public void setDefaultDTM(DTM dtm)
470   {
471     m_dtm = dtm;
472   }
473   
474   /**
475    * Get the DTM for this walker.
476    * 
477    * @return Non-null reference to a DTM.
478    */
479   public DTM getDTM(int node)
480   {
481     //
482     return wi().getXPathContext().getDTM(node);
483   }
484   
485   /**
486    * Returns true if all the nodes in the iteration well be returned in document 
487    * order.
488    * Warning: This can only be called after setRoot has been called!
489    * 
490    * @return true as a default.
491    */
492   public boolean isDocOrdered()
493   {
494     return true;
495   }
496   
497   /**
498    * Returns the axis being iterated, if it is known.
499    * 
500    * @return Axis.CHILD, etc., or -1 if the axis is not known or is of multiple 
501    * types.
502    */
503   public int getAxis()
504   {
505     return m_axis;
506   }
507   
508   /**
509    * This will traverse the heararchy, calling the visitor for 
510    * each member.  If the called visitor method returns 
511    * false, the subtree should not be called.
512    * 
513    * @param owner The owner of the visitor, where that path may be 
514    *              rewritten if needed.
515    * @param visitor The visitor whose appropriate method will be called.
516    */
517   public void callVisitors(ExpressionOwner owner, XPathVisitor visitor)
518   {
519     if(visitor.visitStep(owner, this))
520     {
521         callPredicateVisitors(visitor);
522         if(null != m_nextWalker)
523         {
524             m_nextWalker.callVisitors(this, visitor);
525         }
526     }
527   }
528   
529   /**
530    * @see ExpressionOwner#getExpression()
531    */
532   public Expression getExpression()
533   {
534     return m_nextWalker;
535   }
536 
537   /**
538    * @see ExpressionOwner#setExpression(Expression)
539    */
540   public void setExpression(Expression exp)
541   {
542     exp.exprSetParent(this);
543     m_nextWalker = (AxesWalker)exp;
544   }
545   
546     /**
547      * @see Expression#deepEquals(Expression)
548      */
549     public boolean deepEquals(Expression expr)
550     {
551       if (!super.deepEquals(expr))
552                 return false;
553 
554       AxesWalker walker = (AxesWalker)expr;
555       if(this.m_axis != walker.m_axis)
556         return false;
557 
558       return true;
559     }
560 
561   /**
562    *  The root node of the TreeWalker, as specified when it was created.
563    */
564   transient int m_root = DTM.NULL;
565 
566   /**
567    *  The node at which the TreeWalker is currently positioned.
568    */
569   private transient int m_currentNode = DTM.NULL;
570   
571   /** True if an itteration has not begun.  */
572   transient boolean m_isFresh;
573 
574   /** The next walker in the location step chain.
575    *  @serial  */
576   protected AxesWalker m_nextWalker;
577   
578   /** The previous walker in the location step chain, or null.
579    *  @serial   */
580   AxesWalker m_prevWalker;
581   
582   /** The traversal axis from where the nodes will be filtered. */
583   protected int m_axis = -1;
584 
585   /** The DTM inner traversal class, that corresponds to the super axis. */
586   protected DTMAxisTraverser m_traverser; 
587 }
588
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