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1   // NamespaceSupport.java - generic Namespace support for SAX.
2   // http://www.saxproject.org
3   // Written by David Megginson
4   // This class is in the Public Domain.  NO WARRANTY!
5   // $Id: NamespaceSupport.java,v 1.5 2004/03/19 20:17:54 maartenc Exp $
6   
7   package org.xml.sax.helpers;
8   
9   import java.util.EmptyStackException;
10  import java.util.Enumeration;
11  import java.util.Hashtable;
12  import java.util.Vector;
13  
14  
15  /***
16   * Encapsulate Namespace logic for use by applications using SAX,
17   * or internally by SAX drivers.
18   *
19   * <blockquote>
20   * <em>This module, both source code and documentation, is in the
21   * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
22   * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
23   * for further information.
24   * </blockquote>
25   *
26   * <p>This class encapsulates the logic of Namespace processing: it
27   * tracks the declarations currently in force for each context and
28   * automatically processes qualified XML names into their Namespace
29   * parts; it can also be used in reverse for generating XML qnames
30   * from Namespaces.</p>
31   *
32   * <p>Namespace support objects are reusable, but the reset method
33   * must be invoked between each session.</p>
34   *
35   * <p>Here is a simple session:</p>
36   *
37   * <pre>
38   * String parts[] = new String[3];
39   * NamespaceSupport support = new NamespaceSupport();
40   *
41   * support.pushContext();
42   * support.declarePrefix("", "http://www.w3.org/1999/xhtml");
43   * support.declarePrefix("dc", "http://www.purl.org/dc#");
44   *
45   * parts = support.processName("p", parts, false);
46   * System.out.println("Namespace URI: " + parts[0]);
47   * System.out.println("Local name: " + parts[1]);
48   * System.out.println("Raw name: " + parts[2]);
49   *
50   * parts = support.processName("dc:title", parts, false);
51   * System.out.println("Namespace URI: " + parts[0]);
52   * System.out.println("Local name: " + parts[1]);
53   * System.out.println("Raw name: " + parts[2]);
54   *
55   * support.popContext();
56   * </pre>
57   *
58   * <p>Note that this class is optimized for the use case where most
59   * elements do not contain Namespace declarations: if the same
60   * prefix/URI mapping is repeated for each context (for example), this
61   * class will be somewhat less efficient.</p>
62   *
63   * <p>Although SAX drivers (parsers) may choose to use this class to
64   * implement namespace handling, they are not required to do so.
65   * Applications must track namespace information themselves if they
66   * want to use namespace information.
67   *
68   * @since SAX 2.0
69   * @author David Megginson
70   * @version 2.0.1 (sax2r2)
71   */
72  public class NamespaceSupport
73  {
74  
75  
76      ////////////////////////////////////////////////////////////////////
77      // Constants.
78      ////////////////////////////////////////////////////////////////////
79  
80  
81      /***
82       * The XML Namespace URI as a constant.
83       * The value is <code>http://www.w3.org/XML/1998/namespace</code>
84       * as defined in the "Namespaces in XML" * recommendation.
85       *
86       * <p>This is the Namespace URI that is automatically mapped
87       * to the "xml" prefix.</p>
88       */
89      public final static String XMLNS =
90  	"http://www.w3.org/XML/1998/namespace";
91  
92  
93      /***
94       * The namespace declaration URI as a constant.
95       * The value is <code>http://www.w3.org/xmlns/2000/</code>, as defined
96       * in a backwards-incompatible erratum to the "Namespaces in XML"
97       * recommendation.  Because that erratum postdated SAX2, SAX2 defaults 
98       * to the original recommendation, and does not normally use this URI.
99       * 
100      *
101      * <p>This is the Namespace URI that is optionally applied to
102      * <em>xmlns</em> and <em>xmlns:*</em> attributes, which are used to
103      * declare namespaces.  </p>
104      *
105      * @since SAX 2.1alpha
106      * @see #setNamespaceDeclUris
107      * @see #isNamespaceDeclUris
108      */
109     public final static String NSDECL =
110 	"http://www.w3.org/xmlns/2000/";
111 
112 
113     /***
114      * An empty enumeration.
115      */
116     private final static Enumeration EMPTY_ENUMERATION =
117 	new Vector().elements();
118 
119 
120     ////////////////////////////////////////////////////////////////////
121     // Constructor.
122     ////////////////////////////////////////////////////////////////////
123 
124 
125     /***
126      * Create a new Namespace support object.
127      */
128     public NamespaceSupport ()
129     {
130 	reset();
131     }
132 
133 
134 
135     ////////////////////////////////////////////////////////////////////
136     // Context management.
137     ////////////////////////////////////////////////////////////////////
138 
139 
140     /***
141      * Reset this Namespace support object for reuse.
142      *
143      * <p>It is necessary to invoke this method before reusing the
144      * Namespace support object for a new session.  If namespace
145      * declaration URIs are to be supported, that flag must also
146      * be set to a non-default value.
147      * </p>
148      *
149      * @see #setNamespaceDeclUris
150      */
151     public void reset ()
152     {
153 	contexts = new Context[32];
154 	namespaceDeclUris = false;
155 	contextPos = 0;
156 	contexts[contextPos] = currentContext = new Context();
157 	currentContext.declarePrefix("xml", XMLNS);
158     }
159 
160 
161     /***
162      * Start a new Namespace context.
163      * The new context will automatically inherit
164      * the declarations of its parent context, but it will also keep
165      * track of which declarations were made within this context.
166      *
167      * <p>Event callback code should start a new context once per element.
168      * This means being ready to call this in either of two places.
169      * For elements that don't include namespace declarations, the
170      * <em>ContentHandler.startElement()</em> callback is the right place.
171      * For elements with such a declaration, it'd done in the first
172      * <em>ContentHandler.startPrefixMapping()</em> callback.
173      * A boolean flag can be used to
174      * track whether a context has been started yet.  When either of
175      * those methods is called, it checks the flag to see if a new context
176      * needs to be started.  If so, it starts the context and sets the
177      * flag.  After <em>ContentHandler.startElement()</em>
178      * does that, it always clears the flag.
179      *
180      * <p>Normally, SAX drivers would push a new context at the beginning
181      * of each XML element.  Then they perform a first pass over the
182      * attributes to process all namespace declarations, making
183      * <em>ContentHandler.startPrefixMapping()</em> callbacks.
184      * Then a second pass is made, to determine the namespace-qualified
185      * names for all attributes and for the element name.
186      * Finally all the information for the
187      * <em>ContentHandler.startElement()</em> callback is available,
188      * so it can then be made.
189      *
190      * <p>The Namespace support object always starts with a base context
191      * already in force: in this context, only the "xml" prefix is
192      * declared.</p>
193      *
194      * @see org.xml.sax.ContentHandler
195      * @see #popContext
196      */
197     public void pushContext ()
198     {
199 	int max = contexts.length;
200 
201 	contexts [contextPos].declsOK = false;
202 	contextPos++;
203 
204 				// Extend the array if necessary
205 	if (contextPos >= max) {
206 	    Context newContexts[] = new Context[max*2];
207 	    System.arraycopy(contexts, 0, newContexts, 0, max);
208 	    max *= 2;
209 	    contexts = newContexts;
210 	}
211 
212 				// Allocate the context if necessary.
213 	currentContext = contexts[contextPos];
214 	if (currentContext == null) {
215 	    contexts[contextPos] = currentContext = new Context();
216 	}
217 
218 				// Set the parent, if any.
219 	if (contextPos > 0) {
220 	    currentContext.setParent(contexts[contextPos - 1]);
221 	}
222     }
223 
224 
225     /***
226      * Revert to the previous Namespace context.
227      *
228      * <p>Normally, you should pop the context at the end of each
229      * XML element.  After popping the context, all Namespace prefix
230      * mappings that were previously in force are restored.</p>
231      *
232      * <p>You must not attempt to declare additional Namespace
233      * prefixes after popping a context, unless you push another
234      * context first.</p>
235      *
236      * @see #pushContext
237      */
238     public void popContext ()
239     {
240 	contexts[contextPos].clear();
241 	contextPos--;
242 	if (contextPos < 0) {
243 	    throw new EmptyStackException();
244 	}
245 	currentContext = contexts[contextPos];
246     }
247 
248 
249 
250     ////////////////////////////////////////////////////////////////////
251     // Operations within a context.
252     ////////////////////////////////////////////////////////////////////
253 
254 
255     /***
256      * Declare a Namespace prefix.  All prefixes must be declared
257      * before they are referenced.  For example, a SAX driver (parser)
258      * would scan an element's attributes
259      * in two passes:  first for namespace declarations,
260      * then a second pass using {@link #processName processName()} to
261      * interpret prefixes against (potentially redefined) prefixes.
262      *
263      * <p>This method declares a prefix in the current Namespace
264      * context; the prefix will remain in force until this context
265      * is popped, unless it is shadowed in a descendant context.</p>
266      *
267      * <p>To declare the default element Namespace, use the empty string as
268      * the prefix.</p>
269      *
270      * <p>Note that you must <em>not</em> declare a prefix after
271      * you've pushed and popped another Namespace context, or
272      * treated the declarations phase as complete by processing
273      * a prefixed name.</p>
274      *
275      * <p>Note that there is an asymmetry in this library: {@link
276      * #getPrefix getPrefix} will not return the "" prefix,
277      * even if you have declared a default element namespace.
278      * To check for a default namespace,
279      * you have to look it up explicitly using {@link #getURI getURI}.
280      * This asymmetry exists to make it easier to look up prefixes
281      * for attribute names, where the default prefix is not allowed.</p>
282      *
283      * @param prefix The prefix to declare, or the empty string to
284      *	indicate the default element namespace.  This may never have
285      *	the value "xml" or "xmlns".
286      * @param uri The Namespace URI to associate with the prefix.
287      * @return true if the prefix was legal, false otherwise
288      * @exception IllegalStateException when a prefix is declared
289      *	after looking up a name in the context, or after pushing
290      *	another context on top of it.
291      *
292      * @see #processName
293      * @see #getURI
294      * @see #getPrefix
295      */
296     public boolean declarePrefix (String prefix, String uri)
297     {
298 	if (prefix.equals("xml") || prefix.equals("xmlns")) {
299 	    return false;
300 	} else {
301 	    currentContext.declarePrefix(prefix, uri);
302 	    return true;
303 	}
304     }
305 
306 
307     /***
308      * Process a raw XML qualified name, after all declarations in the
309      * current context have been handled by {@link #declarePrefix
310      * declarePrefix()}.
311      *
312      * <p>This method processes a raw XML qualified name in the
313      * current context by removing the prefix and looking it up among
314      * the prefixes currently declared.  The return value will be the
315      * array supplied by the caller, filled in as follows:</p>
316      *
317      * <dl>
318      * <dt>parts[0]</dt>
319      * <dd>The Namespace URI, or an empty string if none is
320      *  in use.</dd>
321      * <dt>parts[1]</dt>
322      * <dd>The local name (without prefix).</dd>
323      * <dt>parts[2]</dt>
324      * <dd>The original raw name.</dd>
325      * </dl>
326      *
327      * <p>All of the strings in the array will be internalized.  If
328      * the raw name has a prefix that has not been declared, then
329      * the return value will be null.</p>
330      *
331      * <p>Note that attribute names are processed differently than
332      * element names: an unprefixed element name will receive the
333      * default Namespace (if any), while an unprefixed attribute name
334      * will not.</p>
335      *
336      * @param qName The XML qualified name to be processed.
337      * @param parts An array supplied by the caller, capable of
338      *        holding at least three members.
339      * @param isAttribute A flag indicating whether this is an
340      *        attribute name (true) or an element name (false).
341      * @return The supplied array holding three internalized strings 
342      *        representing the Namespace URI (or empty string), the
343      *        local name, and the XML qualified name; or null if there
344      *        is an undeclared prefix.
345      * @see #declarePrefix
346      * @see java.lang.String#intern */
347     public String [] processName (String qName, String parts[],
348 				  boolean isAttribute)
349     {
350 	String myParts[] = currentContext.processName(qName, isAttribute);
351 	if (myParts == null) {
352 	    return null;
353 	} else {
354 	    parts[0] = myParts[0];
355 	    parts[1] = myParts[1];
356 	    parts[2] = myParts[2];
357 	    return parts;
358 	}
359     }
360 
361 
362     /***
363      * Look up a prefix and get the currently-mapped Namespace URI.
364      *
365      * <p>This method looks up the prefix in the current context.
366      * Use the empty string ("") for the default Namespace.</p>
367      *
368      * @param prefix The prefix to look up.
369      * @return The associated Namespace URI, or null if the prefix
370      *         is undeclared in this context.
371      * @see #getPrefix
372      * @see #getPrefixes
373      */
374     public String getURI (String prefix)
375     {
376 	return currentContext.getURI(prefix);
377     }
378 
379 
380     /***
381      * Return an enumeration of all prefixes whose declarations are
382      * active in the current context.
383      * This includes declarations from parent contexts that have
384      * not been overridden.
385      *
386      * <p><strong>Note:</strong> if there is a default prefix, it will not be
387      * returned in this enumeration; check for the default prefix
388      * using the {@link #getURI getURI} with an argument of "".</p>
389      *
390      * @return An enumeration of prefixes (never empty).
391      * @see #getDeclaredPrefixes
392      * @see #getURI
393      */
394     public Enumeration getPrefixes ()
395     {
396 	return currentContext.getPrefixes();
397     }
398 
399 
400     /***
401      * Return one of the prefixes mapped to a Namespace URI.
402      *
403      * <p>If more than one prefix is currently mapped to the same
404      * URI, this method will make an arbitrary selection; if you
405      * want all of the prefixes, use the {@link #getPrefixes}
406      * method instead.</p>
407      *
408      * <p><strong>Note:</strong> this will never return the empty (default) prefix;
409      * to check for a default prefix, use the {@link #getURI getURI}
410      * method with an argument of "".</p>
411      *
412      * @param uri The Namespace URI.
413      * @param isAttribute true if this prefix is for an attribute
414      *        (and the default Namespace is not allowed).
415      * @return One of the prefixes currently mapped to the URI supplied,
416      *         or null if none is mapped or if the URI is assigned to
417      *         the default Namespace.
418      * @see #getPrefixes(java.lang.String)
419      * @see #getURI
420      */
421     public String getPrefix (String uri)
422     {
423 	return currentContext.getPrefix(uri);
424     }
425 
426 
427     /***
428      * Return an enumeration of all prefixes for a given URI whose
429      * declarations are active in the current context.
430      * This includes declarations from parent contexts that have
431      * not been overridden.
432      *
433      * <p>This method returns prefixes mapped to a specific Namespace
434      * URI.  The xml: prefix will be included.  If you want only one
435      * prefix that's mapped to the Namespace URI, and you don't care 
436      * which one you get, use the {@link #getPrefix getPrefix}
437      *  method instead.</p>
438      *
439      * <p><strong>Note:</strong> the empty (default) prefix is <em>never</em> included
440      * in this enumeration; to check for the presence of a default
441      * Namespace, use the {@link #getURI getURI} method with an
442      * argument of "".</p>
443      *
444      * @param uri The Namespace URI.
445      * @return An enumeration of prefixes (never empty).
446      * @see #getPrefix
447      * @see #getDeclaredPrefixes
448      * @see #getURI
449      */
450     public Enumeration getPrefixes (String uri)
451     {
452 	Vector prefixes = new Vector();
453 	Enumeration allPrefixes = getPrefixes();
454 	while (allPrefixes.hasMoreElements()) {
455 	    String prefix = (String)allPrefixes.nextElement();
456 	    if (uri.equals(getURI(prefix))) {
457 		prefixes.addElement(prefix);
458 	    }
459 	}
460 	return prefixes.elements();
461     }
462 
463 
464     /***
465      * Return an enumeration of all prefixes declared in this context.
466      *
467      * <p>The empty (default) prefix will be included in this 
468      * enumeration; note that this behaviour differs from that of
469      * {@link #getPrefix} and {@link #getPrefixes}.</p>
470      *
471      * @return An enumeration of all prefixes declared in this
472      *         context.
473      * @see #getPrefixes
474      * @see #getURI
475      */
476     public Enumeration getDeclaredPrefixes ()
477     {
478 	return currentContext.getDeclaredPrefixes();
479     }
480 
481     /***
482      * Controls whether namespace declaration attributes are placed
483      * into the {@link #NSDECL NSDECL} namespace
484      * by {@link #processName processName()}.  This may only be
485      * changed before any contexts have been pushed.
486      *
487      * @since SAX 2.1alpha
488      *
489      * @exception IllegalStateException when attempting to set this
490      *	after any context has been pushed.
491      */
492     public void setNamespaceDeclUris (boolean value)
493     {
494 	if (contextPos != 0)
495 	    throw new IllegalStateException ();
496 	if (value == namespaceDeclUris)
497 	    return;
498 	namespaceDeclUris = value;
499 	if (value)
500 	    currentContext.declarePrefix ("xmlns", NSDECL);
501 	else {
502 	    contexts[contextPos] = currentContext = new Context();
503 	    currentContext.declarePrefix("xml", XMLNS);
504 	}
505     }
506 
507     /***
508      * Returns true if namespace declaration attributes are placed into
509      * a namespace.  This behavior is not the default.
510      *
511      * @since SAX 2.1alpha
512      */
513     public boolean isNamespaceDeclUris ()
514 	{ return namespaceDeclUris; }
515 
516 
517 
518     ////////////////////////////////////////////////////////////////////
519     // Internal state.
520     ////////////////////////////////////////////////////////////////////
521 
522     private Context contexts[];
523     private Context currentContext;
524     private int contextPos;
525     private boolean namespaceDeclUris;
526 
527 
528     ////////////////////////////////////////////////////////////////////
529     // Internal classes.
530     ////////////////////////////////////////////////////////////////////
531 
532     /***
533      * Internal class for a single Namespace context.
534      *
535      * <p>This module caches and reuses Namespace contexts,
536      * so the number allocated
537      * will be equal to the element depth of the document, not to the total
538      * number of elements (i.e. 5-10 rather than tens of thousands).
539      * Also, data structures used to represent contexts are shared when
540      * possible (child contexts without declarations) to further reduce
541      * the amount of memory that's consumed.
542      * </p>
543      */
544     final class Context {
545 
546 	/***
547 	 * Create the root-level Namespace context.
548 	 */
549 	Context ()
550 	{
551 	    copyTables();
552 	}
553 	
554 	
555 	/***
556 	 * (Re)set the parent of this Namespace context.
557 	 * The context must either have been freshly constructed,
558 	 * or must have been cleared.
559 	 *
560 	 * @param context The parent Namespace context object.
561 	 */
562 	void setParent (Context parent)
563 	{
564 	    this.parent = parent;
565 	    declarations = null;
566 	    prefixTable = parent.prefixTable;
567 	    uriTable = parent.uriTable;
568 	    elementNameTable = parent.elementNameTable;
569 	    attributeNameTable = parent.attributeNameTable;
570 	    defaultNS = parent.defaultNS;
571 	    declSeen = false;
572 	    declsOK = true;
573 	}
574 
575 	/***
576 	 * Makes associated state become collectible,
577 	 * invalidating this context.
578 	 * {@link #setParent} must be called before
579 	 * this context may be used again.
580 	 */
581 	void clear ()
582 	{
583 	    parent = null;
584 	    prefixTable = null;
585 	    uriTable = null;
586 	    elementNameTable = null;
587 	    attributeNameTable = null;
588 	    defaultNS = null;
589 	}
590 	
591 	
592 	/***
593 	 * Declare a Namespace prefix for this context.
594 	 *
595 	 * @param prefix The prefix to declare.
596 	 * @param uri The associated Namespace URI.
597 	 * @see org.xml.sax.helpers.NamespaceSupport#declarePrefix
598 	 */
599 	void declarePrefix (String prefix, String uri)
600 	{
601 				// Lazy processing...
602 	    if (!declsOK)
603 		throw new IllegalStateException (
604 		    "can't declare any more prefixes in this context");
605 	    if (!declSeen) {
606 		copyTables();
607 	    }
608 	    if (declarations == null) {
609 		declarations = new Vector();
610 	    }
611 	    
612 	    prefix = prefix.intern();
613 	    uri = uri.intern();
614 	    if ("".equals(prefix)) {
615 		if ("".equals(uri)) {
616 		    defaultNS = null;
617 		} else {
618 		    defaultNS = uri;
619 		}
620 	    } else {
621 		prefixTable.put(prefix, uri);
622 		uriTable.put(uri, prefix); // may wipe out another prefix
623 	    }
624 	    declarations.addElement(prefix);
625 	}
626 
627 
628 	/***
629 	 * Process an XML qualified name in this context.
630 	 *
631 	 * @param qName The XML qualified name.
632 	 * @param isAttribute true if this is an attribute name.
633 	 * @return An array of three strings containing the
634 	 *         URI part (or empty string), the local part,
635 	 *         and the raw name, all internalized, or null
636 	 *         if there is an undeclared prefix.
637 	 * @see org.xml.sax.helpers.NamespaceSupport#processName
638 	 */
639 	String [] processName (String qName, boolean isAttribute)
640 	{
641 	    String name[];
642 	    Hashtable table;
643 	    
644 	    			// detect errors in call sequence
645 	    declsOK = false;
646 
647 				// Select the appropriate table.
648 	    if (isAttribute) {
649 		table = attributeNameTable;
650 	    } else {
651 		table = elementNameTable;
652 	    }
653 	    
654 				// Start by looking in the cache, and
655 				// return immediately if the name
656 				// is already known in this content
657 	    name = (String[])table.get(qName);
658 	    if (name != null) {
659 		return name;
660 	    }
661 	    
662 				// We haven't seen this name in this
663 				// context before.  Maybe in the parent
664 				// context, but we can't assume prefix
665 				// bindings are the same.
666 	    name = new String[3];
667 	    name[2] = qName.intern();
668 	    int index = qName.indexOf(':');
669 	    
670 	    
671 				// No prefix.
672 	    if (index == -1) {
673 		if (isAttribute) {
674 		    if (qName == "xmlns" && namespaceDeclUris)
675 			name[0] = NSDECL;
676 		    else
677 			name[0] = "";
678 		} else if (defaultNS == null) {
679 		    name[0] = "";
680 		} else {
681 		    name[0] = defaultNS;
682 		}
683 		name[1] = name[2];
684 	    }
685 	    
686 				// Prefix
687 	    else {
688 		String prefix = qName.substring(0, index);
689 		String local = qName.substring(index+1);
690 		String uri;
691 		if ("".equals(prefix)) {
692 		    uri = defaultNS;
693 		} else {
694 		    uri = (String)prefixTable.get(prefix);
695 		}
696 		if (uri == null
697 			|| (!isAttribute && "xmlns".equals (prefix))) {
698 		    return null;
699 		}
700 		name[0] = uri;
701 		name[1] = local.intern();
702 	    }
703 	    
704 				// Save in the cache for future use.
705 				// (Could be shared with parent context...)
706 	    table.put(name[2], name);
707 	    return name;
708 	}
709 	
710 
711 	/***
712 	 * Look up the URI associated with a prefix in this context.
713 	 *
714 	 * @param prefix The prefix to look up.
715 	 * @return The associated Namespace URI, or null if none is
716 	 *         declared.	
717 	 * @see org.xml.sax.helpers.NamespaceSupport#getURI
718 	 */
719 	String getURI (String prefix)
720 	{
721 	    if ("".equals(prefix)) {
722 		return defaultNS;
723 	    } else if (prefixTable == null) {
724 		return null;
725 	    } else {
726 		return (String)prefixTable.get(prefix);
727 	    }
728 	}
729 
730 
731 	/***
732 	 * Look up one of the prefixes associated with a URI in this context.
733 	 *
734 	 * <p>Since many prefixes may be mapped to the same URI,
735 	 * the return value may be unreliable.</p>
736 	 *
737 	 * @param uri The URI to look up.
738 	 * @return The associated prefix, or null if none is declared.
739 	 * @see org.xml.sax.helpers.NamespaceSupport#getPrefix
740 	 */
741 	String getPrefix (String uri)
742 	{
743 	    if (uriTable == null) {
744 		return null;
745 	    } else {
746 		return (String)uriTable.get(uri);
747 	    }
748 	}
749 	
750 	
751 	/***
752 	 * Return an enumeration of prefixes declared in this context.
753 	 *
754 	 * @return An enumeration of prefixes (possibly empty).
755 	 * @see org.xml.sax.helpers.NamespaceSupport#getDeclaredPrefixes
756 	 */
757 	Enumeration getDeclaredPrefixes ()
758 	{
759 	    if (declarations == null) {
760 		return EMPTY_ENUMERATION;
761 	    } else {
762 		return declarations.elements();
763 	    }
764 	}
765 	
766 	
767 	/***
768 	 * Return an enumeration of all prefixes currently in force.
769 	 *
770 	 * <p>The default prefix, if in force, is <em>not</em>
771 	 * returned, and will have to be checked for separately.</p>
772 	 *
773 	 * @return An enumeration of prefixes (never empty).
774 	 * @see org.xml.sax.helpers.NamespaceSupport#getPrefixes
775 	 */
776 	Enumeration getPrefixes ()
777 	{
778 	    if (prefixTable == null) {
779 		return EMPTY_ENUMERATION;
780 	    } else {
781 		return prefixTable.keys();
782 	    }
783 	}
784 	
785 	
786 
787 	////////////////////////////////////////////////////////////////
788 	// Internal methods.
789 	////////////////////////////////////////////////////////////////
790 
791 
792 	/***
793 	 * Copy on write for the internal tables in this context.
794 	 *
795 	 * <p>This class is optimized for the normal case where most
796 	 * elements do not contain Namespace declarations.</p>
797 	 */	
798 	private void copyTables ()
799 	{
800 	    if (prefixTable != null) {
801 		prefixTable = (Hashtable)prefixTable.clone();
802 	    } else {
803 		prefixTable = new Hashtable();
804 	    }
805 	    if (uriTable != null) {
806 		uriTable = (Hashtable)uriTable.clone();
807 	    } else {
808 		uriTable = new Hashtable();
809 	    }
810 	    elementNameTable = new Hashtable();
811 	    attributeNameTable = new Hashtable();
812 	    declSeen = true;
813 	}
814 
815 
816 
817 	////////////////////////////////////////////////////////////////
818 	// Protected state.
819 	////////////////////////////////////////////////////////////////
820 	
821 	Hashtable prefixTable;
822 	Hashtable uriTable;
823 	Hashtable elementNameTable;
824 	Hashtable attributeNameTable;
825 	String defaultNS = null;
826 	boolean declsOK = true;
827 	
828 
829 
830 	////////////////////////////////////////////////////////////////
831 	// Internal state.
832 	////////////////////////////////////////////////////////////////
833 	
834 	private Vector declarations = null;
835 	private boolean declSeen = false;
836 	private Context parent = null;
837     }
838 }
839 
840 // end of NamespaceSupport.java