VariableSafeAbsRef.java revision 9f8118474e9513f7a5b7d2a05e4a0fb15d1a6569 
1/*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the  "License");
7 * you may not use this file except in compliance with the License.
8 * You may obtain a copy of the License at
9 *
10 *     http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18/*
19 * $Id: VariableSafeAbsRef.java 468655 2006-10-28 07:12:06Z minchau $
20 */
21package org.apache.xpath.operations;
22
23import org.apache.xml.dtm.DTMManager;
24import org.apache.xpath.Expression;
25import org.apache.xpath.XPathContext;
26import org.apache.xpath.objects.XNodeSet;
27import org.apache.xpath.objects.XObject;
28
29
30/**
31 * This is a "smart" variable reference that is used in situations where
32 * an absolute path is optimized into a variable reference, but may
33 * be used in some situations where the document context may have changed.
34 * For instance, in select="document(doc/@href)//name[//salary > 7250]", the
35 * root in the predicate will be different for each node in the set.  While
36 * this is easy to detect statically in this case, in other cases static
37 * detection would be very hard or impossible.  So, this class does a dynamic check
38 * to make sure the document context of the referenced variable is the same as
39 * the current document context, and, if it is not, execute the referenced variable's
40 * expression with the current context instead.
41 */
42public class VariableSafeAbsRef extends Variable
43{
44    static final long serialVersionUID = -9174661990819967452L;
45
46  /**
47   * Dereference the variable, and return the reference value.  Note that lazy
48   * evaluation will occur.  If a variable within scope is not found, a warning
49   * will be sent to the error listener, and an empty nodeset will be returned.
50   *
51   *
52   * @param xctxt The runtime execution context.
53   *
54   * @return The evaluated variable, or an empty nodeset if not found.
55   *
56   * @throws javax.xml.transform.TransformerException
57   */
58  public XObject execute(XPathContext xctxt, boolean destructiveOK)
59  	throws javax.xml.transform.TransformerException
60  {
61  	XNodeSet xns = (XNodeSet)super.execute(xctxt, destructiveOK);
62  	DTMManager dtmMgr = xctxt.getDTMManager();
63  	int context = xctxt.getContextNode();
64  	if(dtmMgr.getDTM(xns.getRoot()).getDocument() !=
65  	   dtmMgr.getDTM(context).getDocument())
66  	{
67  		Expression expr = (Expression)xns.getContainedIter();
68  		xns = (XNodeSet)expr.asIterator(xctxt, context);
69  	}
70  	return xns;
71  }
72
73}
74
75