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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: ElemContext.java 468654 2006-10-28 07:09:23Z minchau $
20  */
21 package org.apache.xml.serializer;
22 
23 /**
24  * This class is a stack frame that consists of
25  * information about the element currently being processed
26  * by a serializer. Consider this example:
27  * <pre>
28  *   <A>
29  *     <B1>
30  *     </B1>
31  *     <B2>
32  *     </B2>
33  *   <A>
34  * </pre>
35  *
36  * A stack frame will be pushed for "A" at depth 1,
37  * then another one for "B1" at depth 2.
38  * Then "B1" stackframe is popped.  When the stack frame for "B2" is
39  * pushed, this implementation re-uses the old stack fram object used
40  * by "B1" to be efficient at not creating too many of these object.
41  *
42  * This is by no means a public class, and neither are its fields or methods,
43  * they are all helper fields for a serializer.
44  *
45  * The purpose of this class is to be more consistent with pushing information
46  * when a new element is being serialized and more quickly restoring the old
47  * information about the parent element with a simple pop() when the
48  * child element is done.  Previously there was some redundant and error-prone
49  * calculations going on to retore information.
50  *
51  * @xsl.usage internal
52  */
53 final class ElemContext
54 {
55     // Fields that form the context of the element
56 
57     /**
58      * The nesting depth of the element inside other elements.
59      */
60     final int m_currentElemDepth;
61 
62     /** HTML field, the element description of the HTML element */
63     ElemDesc m_elementDesc = null;
64 
65     /**
66      * The local name of the element.
67      */
68     String m_elementLocalName = null;
69 
70     /**
71      * The fully qualified name of the element (with prefix, if any).
72      */
73     String m_elementName = null;
74 
75     /**
76      * The URI of the element.
77      * If this value is null it means that the URI is not yet determined
78      * for the element. Valid values are the empty string "", meaning
79      * that it is in no namespace, or a string of non-zero length.
80      */
81     String m_elementURI = null;
82 
83     /** If the element is in the cdata-section-names list
84      * then the value is true. If it is true the text children of the element
85      * should be output in CDATA section blocks.
86      */
87     boolean m_isCdataSection;
88 
89     /** True if the current element has output escaping disabled.
90      * This is true for SCRIPT and STYLE elements.
91      */
92     boolean m_isRaw = false;
93 
94     /** The next element "stack frame". This value will only be
95      * set once as deeper stack frames are not deleted when popped off,
96      * but are rather re-used when a push is required.
97      *
98      * This makes for very fast pushing and popping of stack frames
99      * because very few stack frame objects are ever created, they are
100      * mostly re-used.  This re-use saves object creation but it also means
101      * that connections between the frames via m_next and m_prev
102      * never changes either. Just the contents of the frames change
103      * as they are re-used. Only the reference to the current stack frame, which
104      * is held by the serializer is changed via a quick pop() or push().
105      */
106     private ElemContext m_next;
107 
108     /** The previous element "stack frame". */
109     final ElemContext m_prev;
110 
111     /**
112      * Set to true when a start tag is started, or open, but not all the
113      * attributes or namespace information is yet collected.
114      */
115     boolean m_startTagOpen = false;
116 
117     /**
118      * Constructor to create the root of the element contexts.
119      *
120      */
ElemContext()121     ElemContext()
122     {
123         // this assignment means can never pop this context off
124         m_prev = this;
125         // depth 0 because it doesn't correspond to any element
126         m_currentElemDepth = 0;
127     }
128 
129     /**
130      * Constructor to create the "stack frame" for a given element depth.
131      *
132      * This implementation will re-use the context at each depth. If
133      * a documents deepest element depth is N then there will be (N+1)
134      * such objects created, no more than that.
135      *
136      * @param previous The "stack frame" corresponding to the new
137      * elements parent element.
138      */
ElemContext(final ElemContext previous)139     private ElemContext(final ElemContext previous)
140     {
141         m_prev = previous;
142         m_currentElemDepth = previous.m_currentElemDepth + 1;
143     }
144 
145     /**
146      * Pop the current "stack frame".
147      * @return Returns the parent "stack frame" of the one popped.
148      */
pop()149     final ElemContext pop()
150     {
151         /* a very simple pop.  No clean up is done of the deeper
152          * stack frame.  All deeper stack frames are still attached
153          * but dormant, just waiting to be re-used.
154          */
155         return this.m_prev;
156     }
157 
158     /**
159      * This method pushes an element "stack frame"
160      * but with no initialization of values in that frame.
161      * This method is used for optimization purposes, like when pushing
162      * a stack frame for an HTML "IMG" tag which has no children and
163      * the stack frame will almost immediately be popped.
164      */
push()165     final ElemContext push()
166     {
167         ElemContext frame = this.m_next;
168         if (frame == null)
169         {
170             /* We have never been at this depth yet, and there is no
171              * stack frame to re-use, so we now make a new one.
172              */
173             frame = new ElemContext(this);
174             this.m_next = frame;
175         }
176         /*
177          * We shouldn't need to set this true because we should just
178          * be pushing a dummy stack frame that will be instantly popped.
179          * Yet we need to be ready in case this element does have
180          * unexpected children.
181          */
182         frame.m_startTagOpen = true;
183         return frame;
184     }
185 
186     /**
187      * Push an element context on the stack. This context keeps track of
188      * information gathered about the element.
189      * @param uri The URI for the namespace for the element name,
190      * can be null if it is not yet known.
191      * @param localName The local name of the element (no prefix),
192      * can be null.
193      * @param qName The qualified name (with prefix, if any)
194      * of the element, this parameter is required.
195      */
push( final String uri, final String localName, final String qName)196     final ElemContext push(
197         final String uri,
198         final String localName,
199         final String qName)
200     {
201         ElemContext frame = this.m_next;
202         if (frame == null)
203         {
204             /* We have never been at this depth yet, and there is no
205              * stack frame to re-use, so we now make a new one.
206              */
207             frame = new ElemContext(this);
208             this.m_next = frame;
209         }
210 
211         // Initialize, or reset values in the new or re-used stack frame.
212         frame.m_elementName = qName;
213         frame.m_elementLocalName = localName;
214         frame.m_elementURI = uri;
215         frame.m_isCdataSection = false;
216         frame.m_startTagOpen = true;
217 
218         // is_Raw is already set in the HTML startElement() method
219         // frame.m_isRaw = false;
220         return frame;
221     }
222 }
223