NamespaceMappings


1   /*
2    * Copyright 2003-2004 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: NamespaceMappings.java,v 1.6 2004/02/17 04:18:18 minchau Exp $
18   */
19  package org.apache.xml.serializer;
20  
21  import java.util.Enumeration  ;
22  import java.util.Hashtable  ;
23  import java.util.Stack  ;
24  
25  import org.xml.sax.ContentHandler  ;
26  import org.xml.sax.SAXException  ;
27  
28  /**
29   * This class keeps track of the currently defined namespaces. Conceptually the
30   * prefix/uri/depth triplets are pushed on a stack pushed on a stack. The depth
31   * indicates the nesting depth of the element for which the mapping was made.
32   * 
33   * <p>For example:
34   * <pre>
35   * <chapter xmlns:p1="def">
36   *   <paragraph xmlns:p2="ghi">
37   *      <sentance xmlns:p3="jkl">
38   *      </sentance>
39   *    </paragraph>
40   *    <paragraph xlmns:p4="mno">
41   *    </paragraph>
42   * </chapter>
43   * </pre>
44   * 
45   * When the <chapter> element is encounted the prefix "p1" associated with uri
46   * "def" is pushed on the stack with depth 1.
47   * When the first <paragraph> is encountered "p2" and "ghi" are pushed with
48   * depth 2.
49   * When the <sentance> is encountered "p3" and "jkl" are pushed with depth 3.
50   * When </sentance> occurs the popNamespaces(3) will pop "p3"/"jkl" off the
51   * stack.  Of course popNamespaces(2) would pop anything with depth 2 or
52   * greater.
53   * 
54   * So prefix/uri pairs are pushed and poped off the stack as elements are
55   * processed.  At any given moment of processing the currently visible prefixes
56   * are on the stack and a prefix can be found given a uri, or a uri can be found
57   * given a prefix.
58   */
59  public class NamespaceMappings
60  {
61      /**
62       * This member is continually incremented when new prefixes need to be
63       * generated. ("ns0"  "ns1" ...)
64       */
65      private int count = 0;
66  
67      /**
68       * Stack of prefixes that have mappings
69       * The top of this stack is the prefix that was last mapped to an URI
70       * 
71       * For every prefix pushed on this stack a corresponding integer is pushed
72       * on the m_nodeStack. That way all prefixes pushed at the current depth can
73       * be removed at the same time.      
74       */
75      private java.util.Stack   m_prefixStack = new Stack  ();
76  
77      /**
78       * Each entry (prefix) in this hashtable points to a Stack of URIs
79       */
80      private Hashtable   m_namespaces = new Hashtable  ();
81  
82      /** 
83       * The top of this stack contains the nested element depth
84       * of the last declared a namespace.
85       * Used to know how many prefix mappings to pop when leaving
86       * the current element depth.
87       * For every prefix mapping the current element depth is 
88       * pushed on this stack, as well as the prefix on the m_prefixStack
89       * That way all prefixes pushed at the current depth can be 
90       * removed at the same time.
91       * Used to ensure prefix/uri map scopes are closed correctly
92       *
93       */
94      private Stack   m_nodeStack = new Stack  ();
95  
96      private static final String   EMPTYSTRING = "";
97      private static final String   XML_PREFIX = "xml"; // was "xmlns"
98  
99      /**
100      * Default constructor
101      * @see java.lang.Object#Object()
102      */
103     public NamespaceMappings()
104     {
105         initNamespaces();
106     }
107 
108     /**
109      * This method initializes the namespace object with appropriate stacks
110      * and predefines a few prefix/uri pairs which always exist.
111      */
112     private void initNamespaces()
113     {
114  
115 
116         // Define the default namespace (initially maps to "" uri)
117         Stack   stack;
118         m_namespaces.put(EMPTYSTRING, stack = new Stack  ());
119         stack.push(EMPTYSTRING);
120         m_prefixStack.push(EMPTYSTRING);
121 
122         m_namespaces.put(XML_PREFIX, stack = new Stack  ());
123         stack.push("http://www.w3.org/XML/1998/namespace");
124         m_prefixStack.push(XML_PREFIX);
125 
126         m_nodeStack.push(new Integer  (-1));
127 
128     }
129 
130     /**
131      * Use a namespace prefix to lookup a namespace URI.
132      * 
133      * @param prefix String the prefix of the namespace
134      * @return the URI corresponding to the prefix
135      */
136     public String   lookupNamespace(String   prefix)
137     {
138         final Stack   stack = (Stack  ) m_namespaces.get(prefix);
139         return stack != null && !stack.isEmpty() ? (String  ) stack.peek() : null;
140     }
141 
142     /**
143      * Given a namespace uri, and the namespaces mappings for the 
144      * current element, return the current prefix for that uri.
145      * 
146      * @param uri the namespace URI to be search for
147      * @return an existing prefix that maps to the given URI, null if no prefix
148      * maps to the given namespace URI.
149      */
150     public String   lookupPrefix(String   uri)
151     {
152         String   foundPrefix = null;
153         Enumeration   prefixes = m_namespaces.keys();
154         while (prefixes.hasMoreElements())
155         {
156             String   prefix = (String  ) prefixes.nextElement();
157             String   uri2 = lookupNamespace(prefix);
158             if (uri2 != null && uri2.equals(uri))
159             {
160                 foundPrefix = prefix;
161                 break;
162             }
163         }
164         return foundPrefix;
165     }
166 
167     /**
168      * Undeclare the namespace that is currently pointed to by a given prefix
169      */
170     public boolean popNamespace(String   prefix)
171     {
172         // Prefixes "xml" and "xmlns" cannot be redefined
173         if (prefix.startsWith(XML_PREFIX))
174         {
175             return false;
176         }
177 
178         Stack   stack;
179         if ((stack = (Stack  ) m_namespaces.get(prefix)) != null)
180         {
181             stack.pop();
182             return true;
183         }
184         return false;
185     }
186 
187     /**
188      * Declare a prefix to point to a namespace URI
189      * @param prefix a String with the prefix for a qualified name
190      * @param uri a String with the uri to which the prefix is to map
191      * @param elemDepth the depth of current declaration
192      */
193     public boolean pushNamespace(String   prefix, String   uri, int elemDepth)
194     {
195         // Prefixes "xml" and "xmlns" cannot be redefined
196         if (prefix.startsWith(XML_PREFIX))
197         {
198             return false;
199         }
200 
201         Stack   stack;
202         // Get the stack that contains URIs for the specified prefix
203         if ((stack = (Stack  ) m_namespaces.get(prefix)) == null)
204         {
205             m_namespaces.put(prefix, stack = new Stack  ());
206         }
207 
208         if (!stack.empty() && uri.equals(stack.peek()))
209         {
210             return false;
211         }
212 
213         stack.push(uri);
214         m_prefixStack.push(prefix);
215         m_nodeStack.push(new Integer  (elemDepth));
216         return true;
217     }
218 
219     /**
220      * Pop, or undeclare all namespace definitions that are currently
221      * declared at the given element depth, or deepter.
222      * @param elemDepth the element depth for which mappings declared at this
223      * depth or deeper will no longer be valid
224      * @param saxHandler The ContentHandler to notify of any endPrefixMapping()
225      * calls.  This parameter can be null.
226      */
227     public void popNamespaces(int elemDepth, ContentHandler   saxHandler)
228     {
229         while (true)
230         {
231             if (m_nodeStack.isEmpty())
232                 return;
233             Integer   i = (Integer  ) (m_nodeStack.peek());
234             if (i.intValue() < elemDepth)
235                 return;
236             /* the depth of the declared mapping is elemDepth or deeper
237              * so get rid of it
238              */
239 
240             m_nodeStack.pop();
241             final String   prefix = (String  ) m_prefixStack.pop(); 
242             popNamespace(prefix);
243             if (saxHandler != null)
244             {
245                 try
246                 {
247                     saxHandler.endPrefixMapping(prefix);
248                 }
249                 catch (SAXException   e)
250                 {
251                     // not much we can do if they aren't willing to listen
252                 }
253             }
254                
255         }
256     }
257 
258     /**
259      * Generate a new namespace prefix ( ns0, ns1 ...) not used before
260      * @return String a new namespace prefix ( ns0, ns1, ns2 ...)
261      */
262     public String   generateNextPrefix()
263     {
264         return "ns" + (count++);
265     }
266 
267  
268     /**
269      * This method makes a clone of this object.
270      *
271      */
272     public Object   clone() throws CloneNotSupportedException   {
273         NamespaceMappings clone = new NamespaceMappings();
274         clone.m_prefixStack = (Stack  )m_prefixStack.clone();
275         clone.m_nodeStack = (Stack  ) m_nodeStack.clone();
276         clone.m_namespaces = (Hashtable  ) m_namespaces.clone();
277         
278         clone.count = count;
279         return clone;
280         
281     }
282     
283     public final void reset()
284     {
285         this.count = 0;
286         this.m_namespaces.clear();
287         this.m_nodeStack.clear();
288         this.m_prefixStack.clear();
289         
290         initNamespaces();
291     }
292 
293 }
294
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