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 226184 2005-04-08 10:53:24Z neeraj $
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 contextPos++;
202
203 // Extend the array if necessary
204 if (contextPos >= max) {
205 Context newContexts[] = new Context[max*2];
206 System.arraycopy(contexts, 0, newContexts, 0, max);
207 max *= 2;
208 contexts = newContexts;
209 }
210
211 // Allocate the context if necessary.
212 currentContext = contexts[contextPos];
213 if (currentContext == null) {
214 contexts[contextPos] = currentContext = new Context();
215 }
216
217 // Set the parent, if any.
218 if (contextPos > 0) {
219 currentContext.setParent(contexts[contextPos - 1]);
220 }
221 }
222
223
224 /**
225 * Revert to the previous Namespace context.
226 *
227 * <p>Normally, you should pop the context at the end of each
228 * XML element. After popping the context, all Namespace prefix
229 * mappings that were previously in force are restored.</p>
230 *
231 * <p>You must not attempt to declare additional Namespace
232 * prefixes after popping a context, unless you push another
233 * context first.</p>
234 *
235 * @see #pushContext
236 */
237 public void popContext ()
238 {
239 contexts[contextPos].clear();
240 contextPos--;
241 if (contextPos < 0) {
242 throw new EmptyStackException();
243 }
244 currentContext = contexts[contextPos];
245 }
246
247
248
249 ////////////////////////////////////////////////////////////////////
250 // Operations within a context.
251 ////////////////////////////////////////////////////////////////////
252
253
254 /**
255 * Declare a Namespace prefix. All prefixes must be declared
256 * before they are referenced. For example, a SAX driver (parser)
257 * would scan an element's attributes
258 * in two passes: first for namespace declarations,
259 * then a second pass using {@link #processName processName()} to
260 * interpret prefixes against (potentially redefined) prefixes.
261 *
262 * <p>This method declares a prefix in the current Namespace
263 * context; the prefix will remain in force until this context
264 * is popped, unless it is shadowed in a descendant context.</p>
265 *
266 * <p>To declare the default element Namespace, use the empty string as
267 * the prefix.</p>
268 *
269 * <p>Note that there is an asymmetry in this library: {@link
270 * #getPrefix getPrefix} will not return the "" prefix,
271 * even if you have declared a default element namespace.
272 * To check for a default namespace,
273 * you have to look it up explicitly using {@link #getURI getURI}.
274 * This asymmetry exists to make it easier to look up prefixes
275 * for attribute names, where the default prefix is not allowed.</p>
276 *
277 * @param prefix The prefix to declare, or the empty string to
278 * indicate the default element namespace. This may never have
279 * the value "xml" or "xmlns".
280 * @param uri The Namespace URI to associate with the prefix.
281 * @return true if the prefix was legal, false otherwise
282 *
283 * @see #processName
284 * @see #getURI
285 * @see #getPrefix
286 */
287 public boolean declarePrefix (String prefix, String uri)
288 {
289 if (prefix.equals("xml") || prefix.equals("xmlns")) {
290 return false;
291 } else {
292 currentContext.declarePrefix(prefix, uri);
293 return true;
294 }
295 }
296
297
298 /**
299 * Process a raw XML qualified name, after all declarations in the
300 * current context have been handled by {@link #declarePrefix
301 * declarePrefix()}.
302 *
303 * <p>This method processes a raw XML qualified name in the
304 * current context by removing the prefix and looking it up among
305 * the prefixes currently declared. The return value will be the
306 * array supplied by the caller, filled in as follows:</p>
307 *
308 * <dl>
309 * <dt>parts[0]</dt>
310 * <dd>The Namespace URI, or an empty string if none is
311 * in use.</dd>
312 * <dt>parts[1]</dt>
313 * <dd>The local name (without prefix).</dd>
314 * <dt>parts[2]</dt>
315 * <dd>The original raw name.</dd>
316 * </dl>
317 *
318 * <p>All of the strings in the array will be internalized. If
319 * the raw name has a prefix that has not been declared, then
320 * the return value will be null.</p>
321 *
322 * <p>Note that attribute names are processed differently than
323 * element names: an unprefixed element name will receive the
324 * default Namespace (if any), while an unprefixed attribute name
325 * will not.</p>
326 *
327 * @param qName The XML qualified name to be processed.
328 * @param parts An array supplied by the caller, capable of
329 * holding at least three members.
330 * @param isAttribute A flag indicating whether this is an
331 * attribute name (true) or an element name (false).
332 * @return The supplied array holding three internalized strings
333 * representing the Namespace URI (or empty string), the
334 * local name, and the XML qualified name; or null if there
335 * is an undeclared prefix.
336 * @see #declarePrefix
337 * @see java.lang.String#intern */
338 public String [] processName (String qName, String parts[],
339 boolean isAttribute)
340 {
341 String myParts[] = currentContext.processName(qName, isAttribute);
342 if (myParts == null) {
343 return null;
344 } else {
345 parts[0] = myParts[0];
346 parts[1] = myParts[1];
347 parts[2] = myParts[2];
348 return parts;
349 }
350 }
351
352
353 /**
354 * Look up a prefix and get the currently-mapped Namespace URI.
355 *
356 * <p>This method looks up the prefix in the current context.
357 * Use the empty string ("") for the default Namespace.</p>
358 *
359 * @param prefix The prefix to look up.
360 * @return The associated Namespace URI, or null if the prefix
361 * is undeclared in this context.
362 * @see #getPrefix
363 * @see #getPrefixes
364 */
365 public String getURI (String prefix)
366 {
367 return currentContext.getURI(prefix);
368 }
369
370
371 /**
372 * Return an enumeration of all prefixes whose declarations are
373 * active in the current context.
374 * This includes declarations from parent contexts that have
375 * not been overridden.
376 *
377 * <p><strong>Note:</strong> if there is a default prefix, it will not be
378 * returned in this enumeration; check for the default prefix
379 * using the {@link #getURI getURI} with an argument of "".</p>
380 *
381 * @return An enumeration of prefixes (never empty).
382 * @see #getDeclaredPrefixes
383 * @see #getURI
384 */
385 public Enumeration getPrefixes ()
386 {
387 return currentContext.getPrefixes();
388 }
389
390
391 /**
392 * Return one of the prefixes mapped to a Namespace URI.
393 *
394 * <p>If more than one prefix is currently mapped to the same
395 * URI, this method will make an arbitrary selection; if you
396 * want all of the prefixes, use the {@link #getPrefixes}
397 * method instead.</p>
398 *
399 * <p><strong>Note:</strong> this will never return the empty (default) prefix;
400 * to check for a default prefix, use the {@link #getURI getURI}
401 * method with an argument of "".</p>
402 *
403 * @param uri the namespace URI
404 * @return one of the prefixes currently mapped to the URI supplied,
405 * or null if none is mapped or if the URI is assigned to
406 * the default namespace
407 * @see #getPrefixes(java.lang.String)
408 * @see #getURI
409 */
410 public String getPrefix (String uri)
411 {
412 return currentContext.getPrefix(uri);
413 }
414
415
416 /**
417 * Return an enumeration of all prefixes for a given URI whose
418 * declarations are active in the current context.
419 * This includes declarations from parent contexts that have
420 * not been overridden.
421 *
422 * <p>This method returns prefixes mapped to a specific Namespace
423 * URI. The xml: prefix will be included. If you want only one
424 * prefix that's mapped to the Namespace URI, and you don't care
425 * which one you get, use the {@link #getPrefix getPrefix}
426 * method instead.</p>
427 *
428 * <p><strong>Note:</strong> the empty (default) prefix is <em>never</em> included
429 * in this enumeration; to check for the presence of a default
430 * Namespace, use the {@link #getURI getURI} method with an
431 * argument of "".</p>
432 *
433 * @param uri The Namespace URI.
434 * @return An enumeration of prefixes (never empty).
435 * @see #getPrefix
436 * @see #getDeclaredPrefixes
437 * @see #getURI
438 */
439 public Enumeration getPrefixes (String uri)
440 {
441 Vector prefixes = new Vector();
442 Enumeration allPrefixes = getPrefixes();
443 while (allPrefixes.hasMoreElements()) {
444 String prefix = (String)allPrefixes.nextElement();
445 if (uri.equals(getURI(prefix))) {
446 prefixes.addElement(prefix);
447 }
448 }
449 return prefixes.elements();
450 }
451
452
453 /**
454 * Return an enumeration of all prefixes declared in this context.
455 *
456 * <p>The empty (default) prefix will be included in this
457 * enumeration; note that this behaviour differs from that of
458 * {@link #getPrefix} and {@link #getPrefixes}.</p>
459 *
460 * @return An enumeration of all prefixes declared in this
461 * context.
462 * @see #getPrefixes
463 * @see #getURI
464 */
465 public Enumeration getDeclaredPrefixes ()
466 {
467 return currentContext.getDeclaredPrefixes();
468 }
469
470 /**
471 * Controls whether namespace declaration attributes are placed
472 * into the {@link #NSDECL NSDECL} namespace
473 * by {@link #processName processName()}. This may only be
474 * changed before any contexts have been pushed.
475 *
476 * @since SAX 2.1alpha
477 *
478 * @exception IllegalStateException when attempting to set this
479 * after any context has been pushed.
480 */
481 public void setNamespaceDeclUris (boolean value)
482 {
483 if (contextPos != 0)
484 throw new IllegalStateException ();
485 if (value == namespaceDeclUris)
486 return;
487 namespaceDeclUris = value;
488 if (value)
489 currentContext.declarePrefix ("xmlns", NSDECL);
490 else {
491 contexts[contextPos] = currentContext = new Context();
492 currentContext.declarePrefix("xml", XMLNS);
493 }
494 }
495
496 /**
497 * Returns true if namespace declaration attributes are placed into
498 * a namespace. This behavior is not the default.
499 *
500 * @since SAX 2.1alpha
501 */
502 public boolean isNamespaceDeclUris ()
503 { return namespaceDeclUris; }
504
505
506
507 ////////////////////////////////////////////////////////////////////
508 // Internal state.
509 ////////////////////////////////////////////////////////////////////
510
511 private Context contexts[];
512 private Context currentContext;
513 private int contextPos;
514 private boolean namespaceDeclUris;
515
516
517 ////////////////////////////////////////////////////////////////////
518 // Internal classes.
519 ////////////////////////////////////////////////////////////////////
520
521 /**
522 * Internal class for a single Namespace context.
523 *
524 * <p>This module caches and reuses Namespace contexts,
525 * so the number allocated
526 * will be equal to the element depth of the document, not to the total
527 * number of elements (i.e. 5-10 rather than tens of thousands).
528 * Also, data structures used to represent contexts are shared when
529 * possible (child contexts without declarations) to further reduce
530 * the amount of memory that's consumed.
531 * </p>
532 */
533 final class Context {
534
535 /**
536 * Create the root-level Namespace context.
537 */
538 Context ()
539 {
540 copyTables();
541 }
542
543
544 /**
545 * (Re)set the parent of this Namespace context.
546 * The context must either have been freshly constructed,
547 * or must have been cleared.
548 *
549 * @param context The parent Namespace context object.
550 */
551 void setParent (Context parent)
552 {
553 this.parent = parent;
554 declarations = null;
555 prefixTable = parent.prefixTable;
556 uriTable = parent.uriTable;
557 elementNameTable = parent.elementNameTable;
558 attributeNameTable = parent.attributeNameTable;
559 defaultNS = parent.defaultNS;
560 declSeen = false;
561 }
562
563 /**
564 * Makes associated state become collectible,
565 * invalidating this context.
566 * {@link #setParent} must be called before
567 * this context may be used again.
568 */
569 void clear ()
570 {
571 parent = null;
572 prefixTable = null;
573 uriTable = null;
574 elementNameTable = null;
575 attributeNameTable = null;
576 defaultNS = null;
577 }
578
579
580 /**
581 * Declare a Namespace prefix for this context.
582 *
583 * @param prefix The prefix to declare.
584 * @param uri The associated Namespace URI.
585 * @see org.xml.sax.helpers.NamespaceSupport#declarePrefix
586 */
587 void declarePrefix (String prefix, String uri)
588 {
589 // Lazy processing...
590 // if (!declsOK)
591 // throw new IllegalStateException (
592 // "can't declare any more prefixes in this context");
593 if (!declSeen) {
594 copyTables();
595 }
596 if (declarations == null) {
597 declarations = new Vector();
598 }
599
600 prefix = prefix.intern();
601 uri = uri.intern();
602 if ("".equals(prefix)) {
603 if ("".equals(uri)) {
604 defaultNS = null;
605 } else {
606 defaultNS = uri;
607 }
608 } else {
609 prefixTable.put(prefix, uri);
610 uriTable.put(uri, prefix); // may wipe out another prefix
611 }
612 declarations.addElement(prefix);
613 }
614
615
616 /**
617 * Process an XML qualified name in this context.
618 *
619 * @param qName The XML qualified name.
620 * @param isAttribute true if this is an attribute name.
621 * @return An array of three strings containing the
622 * URI part (or empty string), the local part,
623 * and the raw name, all internalized, or null
624 * if there is an undeclared prefix.
625 * @see org.xml.sax.helpers.NamespaceSupport#processName
626 */
627 String [] processName (String qName, boolean isAttribute)
628 {
629 String name[];
630 Hashtable table;
631
632 // Select the appropriate table.
633 if (isAttribute) {
634 table = attributeNameTable;
635 } else {
636 table = elementNameTable;
637 }
638
639 // Start by looking in the cache, and
640 // return immediately if the name
641 // is already known in this content
642 name = (String[])table.get(qName);
643 if (name != null) {
644 return name;
645 }
646
647 // We haven't seen this name in this
648 // context before. Maybe in the parent
649 // context, but we can't assume prefix
650 // bindings are the same.
651 name = new String[3];
652 name[2] = qName.intern();
653 int index = qName.indexOf(':');
654
655
656 // No prefix.
657 if (index == -1) {
658 if (isAttribute) {
659 if (qName == "xmlns" && namespaceDeclUris)
660 name[0] = NSDECL;
661 else
662 name[0] = "";
663 } else if (defaultNS == null) {
664 name[0] = "";
665 } else {
666 name[0] = defaultNS;
667 }
668 name[1] = name[2];
669 }
670
671 // Prefix
672 else {
673 String prefix = qName.substring(0, index);
674 String local = qName.substring(index+1);
675 String uri;
676 if ("".equals(prefix)) {
677 uri = defaultNS;
678 } else {
679 uri = (String)prefixTable.get(prefix);
680 }
681 if (uri == null
682 || (!isAttribute && "xmlns".equals (prefix))) {
683 return null;
684 }
685 name[0] = uri;
686 name[1] = local.intern();
687 }
688
689 // Save in the cache for future use.
690 // (Could be shared with parent context...)
691 table.put(name[2], name);
692 return name;
693 }
694
695
696 /**
697 * Look up the URI associated with a prefix in this context.
698 *
699 * @param prefix The prefix to look up.
700 * @return The associated Namespace URI, or null if none is
701 * declared.
702 * @see org.xml.sax.helpers.NamespaceSupport#getURI
703 */
704 String getURI (String prefix)
705 {
706 if ("".equals(prefix)) {
707 return defaultNS;
708 } else if (prefixTable == null) {
709 return null;
710 } else {
711 return (String)prefixTable.get(prefix);
712 }
713 }
714
715
716 /**
717 * Look up one of the prefixes associated with a URI in this context.
718 *
719 * <p>Since many prefixes may be mapped to the same URI,
720 * the return value may be unreliable.</p>
721 *
722 * @param uri The URI to look up.
723 * @return The associated prefix, or null if none is declared.
724 * @see org.xml.sax.helpers.NamespaceSupport#getPrefix
725 */
726 String getPrefix (String uri)
727 {
728 if (uriTable == null) {
729 return null;
730 } else {
731 return (String)uriTable.get(uri);
732 }
733 }
734
735
736 /**
737 * Return an enumeration of prefixes declared in this context.
738 *
739 * @return An enumeration of prefixes (possibly empty).
740 * @see org.xml.sax.helpers.NamespaceSupport#getDeclaredPrefixes
741 */
742 Enumeration getDeclaredPrefixes ()
743 {
744 if (declarations == null) {
745 return EMPTY_ENUMERATION;
746 } else {
747 return declarations.elements();
748 }
749 }
750
751
752 /**
753 * Return an enumeration of all prefixes currently in force.
754 *
755 * <p>The default prefix, if in force, is <em>not</em>
756 * returned, and will have to be checked for separately.</p>
757 *
758 * @return An enumeration of prefixes (never empty).
759 * @see org.xml.sax.helpers.NamespaceSupport#getPrefixes
760 */
761 Enumeration getPrefixes ()
762 {
763 if (prefixTable == null) {
764 return EMPTY_ENUMERATION;
765 } else {
766 return prefixTable.keys();
767 }
768 }
769
770
771
772 ////////////////////////////////////////////////////////////////
773 // Internal methods.
774 ////////////////////////////////////////////////////////////////
775
776
777 /**
778 * Copy on write for the internal tables in this context.
779 *
780 * <p>This class is optimized for the normal case where most
781 * elements do not contain Namespace declarations.</p>
782 */
783 private void copyTables ()
784 {
785 if (prefixTable != null) {
786 prefixTable = (Hashtable)prefixTable.clone();
787 } else {
788 prefixTable = new Hashtable();
789 }
790 if (uriTable != null) {
791 uriTable = (Hashtable)uriTable.clone();
792 } else {
793 uriTable = new Hashtable();
794 }
795 elementNameTable = new Hashtable();
796 attributeNameTable = new Hashtable();
797 declSeen = true;
798 }
799
800
801
802 ////////////////////////////////////////////////////////////////
803 // Protected state.
804 ////////////////////////////////////////////////////////////////
805
806 Hashtable prefixTable;
807 Hashtable uriTable;
808 Hashtable elementNameTable;
809 Hashtable attributeNameTable;
810 String defaultNS = null;
811
812
813
814 ////////////////////////////////////////////////////////////////
815 // Internal state.
816 ////////////////////////////////////////////////////////////////
817
818 private Vector declarations = null;
819 private boolean declSeen = false;
820 private Context parent = null;
821 }
822 }
823
824 // end of NamespaceSupport.java