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 */
21package 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 */
53final 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     */
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     */
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     */
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     */
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     */
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