1 /*
2 * Copyright 2000-2007 Sun Microsystems, Inc. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25
26 package javax.imageio.spi;
27
28 import java.io.File;
29 import java.util.ArrayList;
30 import java.util.HashMap;
31 import java.util.Iterator;
32 import java.util.List;
33 import java.util.Map;
34 import java.util.NoSuchElementException;
35 import java.util.Set;
36 import java.util.ServiceLoader;
37
38 /**
39 * A registry for service provider instances.
40 *
41 * <p> A <i>service</i> is a well-known set of interfaces and (usually
42 * abstract) classes. A <i>service provider</i> is a specific
43 * implementation of a service. The classes in a provider typically
44 * implement the interface or subclass the class defined by the
45 * service itself.
46 *
47 * <p> Service providers are stored in one or more <i>categories</i>,
48 * each of which is defined by a class of interface (described by a
49 * <code>Class</code> object) that all of its members must implement.
50 * The set of categories may be changed dynamically.
51 *
52 * <p> Only a single instance of a given leaf class (that is, the
53 * actual class returned by <code>getClass()</code>, as opposed to any
54 * inherited classes or interfaces) may be registered. That is,
55 * suppose that the
56 * <code>com.mycompany.mypkg.GreenServiceProvider</code> class
57 * implements the <code>com.mycompany.mypkg.MyService</code>
58 * interface. If a <code>GreenServiceProvider</code> instance is
59 * registered, it will be stored in the category defined by the
60 * <code>MyService</code> class. If a new instance of
61 * <code>GreenServiceProvider</code> is registered, it will replace
62 * the previous instance. In practice, service provider objects are
63 * usually singletons so this behavior is appropriate.
64 *
65 * <p> To declare a service provider, a <code>services</code>
66 * subdirectory is placed within the <code>META-INF</code> directory
67 * that is present in every JAR file. This directory contains a file
68 * for each service provider interface that has one or more
69 * implementation classes present in the JAR file. For example, if
70 * the JAR file contained a class named
71 * <code>com.mycompany.mypkg.MyServiceImpl</code> which implements the
72 * <code>javax.someapi.SomeService</code> interface, the JAR file
73 * would contain a file named: <pre>
74 * META-INF/services/javax.someapi.SomeService </pre>
75 *
76 * containing the line:
77 *
78 * <pre>
79 * com.mycompany.mypkg.MyService
80 * </pre>
81 *
82 * <p> The service provider classes should be to be lightweight and
83 * quick to load. Implementations of these interfaces should avoid
84 * complex dependencies on other classes and on native code. The usual
85 * pattern for more complex services is to register a lightweight
86 * proxy for the heavyweight service.
87 *
88 * <p> An application may customize the contents of a registry as it
89 * sees fit, so long as it has the appropriate runtime permission.
90 *
91 * <p> For more details on declaring service providers, and the JAR
92 * format in general, see the <a
93 * href="../../../../technotes/guides/jar/jar.html">
94 * JAR File Specification</a>.
95 *
96 * @see RegisterableService
97 *
98 */
99 public class ServiceRegistry {
100
101 // Class -> Registry
102 private Map categoryMap = new HashMap();
103
104 /**
105 * Constructs a <code>ServiceRegistry</code> instance with a
106 * set of categories taken from the <code>categories</code>
107 * argument.
108 *
109 * @param categories an <code>Iterator</code> containing
110 * <code>Class</code> objects to be used to define categories.
111 *
112 * @exception IllegalArgumentException if
113 * <code>categories</code> is <code>null</code>.
114 */
115 public ServiceRegistry(Iterator<Class<?>> categories) {
116 if (categories == null) {
117 throw new IllegalArgumentException("categories == null!");
118 }
119 while (categories.hasNext()) {
120 Class category = (Class)categories.next();
121 SubRegistry reg = new SubRegistry(this, category);
122 categoryMap.put(category, reg);
123 }
124 }
125
126 // The following two methods expose functionality from
127 // sun.misc.Service. If that class is made public, they may be
128 // removed.
129 //
130 // The sun.misc.ServiceConfigurationError class may also be
131 // exposed, in which case the references to 'an
132 // <code>Error</code>' below should be changed to 'a
133 // <code>ServiceConfigurationError</code>'.
134
135 /**
136 * Searches for implementations of a particular service class
137 * using the given class loader.
138 *
139 * <p> This method transforms the name of the given service class
140 * into a provider-configuration filename as described in the
141 * class comment and then uses the <code>getResources</code>
142 * method of the given class loader to find all available files
143 * with that name. These files are then read and parsed to
144 * produce a list of provider-class names. The iterator that is
145 * returned uses the given class loader to look up and then
146 * instantiate each element of the list.
147 *
148 * <p> Because it is possible for extensions to be installed into
149 * a running Java virtual machine, this method may return
150 * different results each time it is invoked.
151 *
152 * @param providerClass a <code>Class</code>object indicating the
153 * class or interface of the service providers being detected.
154 *
155 * @param loader the class loader to be used to load
156 * provider-configuration files and instantiate provider classes,
157 * or <code>null</code> if the system class loader (or, failing that
158 * the bootstrap class loader) is to be used.
159 *
160 * @return An <code>Iterator</code> that yields provider objects
161 * for the given service, in some arbitrary order. The iterator
162 * will throw an <code>Error</code> if a provider-configuration
163 * file violates the specified format or if a provider class
164 * cannot be found and instantiated.
165 *
166 * @exception IllegalArgumentException if
167 * <code>providerClass</code> is <code>null</code>.
168 */
169 public static <T> Iterator<T> lookupProviders(Class<T> providerClass,
170 ClassLoader loader)
171 {
172 if (providerClass == null) {
173 throw new IllegalArgumentException("providerClass == null!");
174 }
175 return ServiceLoader.load(providerClass, loader).iterator();
176 }
177
178 /**
179 * Locates and incrementally instantiates the available providers
180 * of a given service using the context class loader. This
181 * convenience method is equivalent to:
182 *
183 * <pre>
184 * ClassLoader cl = Thread.currentThread().getContextClassLoader();
185 * return Service.providers(service, cl);
186 * </pre>
187 *
188 * @param providerClass a <code>Class</code>object indicating the
189 * class or interface of the service providers being detected.
190 *
191 * @return An <code>Iterator</code> that yields provider objects
192 * for the given service, in some arbitrary order. The iterator
193 * will throw an <code>Error</code> if a provider-configuration
194 * file violates the specified format or if a provider class
195 * cannot be found and instantiated.
196 *
197 * @exception IllegalArgumentException if
198 * <code>providerClass</code> is <code>null</code>.
199 */
200 public static <T> Iterator<T> lookupProviders(Class<T> providerClass) {
201 if (providerClass == null) {
202 throw new IllegalArgumentException("providerClass == null!");
203 }
204 return ServiceLoader.load(providerClass).iterator();
205 }
206
207 /**
208 * Returns an <code>Iterator</code> of <code>Class</code> objects
209 * indicating the current set of categories. The iterator will be
210 * empty if no categories exist.
211 *
212 * @return an <code>Iterator</code> containing
213 * <code>Class</code>objects.
214 */
215 public Iterator<Class<?>> getCategories() {
216 Set keySet = categoryMap.keySet();
217 return keySet.iterator();
218 }
219
220 /**
221 * Returns an Iterator containing the subregistries to which the
222 * provider belongs.
223 */
224 private Iterator getSubRegistries(Object provider) {
225 List l = new ArrayList();
226 Iterator iter = categoryMap.keySet().iterator();
227 while (iter.hasNext()) {
228 Class c = (Class)iter.next();
229 if (c.isAssignableFrom(provider.getClass())) {
230 l.add((SubRegistry)categoryMap.get(c));
231 }
232 }
233 return l.iterator();
234 }
235
236 /**
237 * Adds a service provider object to the registry. The provider
238 * is associated with the given category.
239 *
240 * <p> If <code>provider</code> implements the
241 * <code>RegisterableService</code> interface, its
242 * <code>onRegistration</code> method will be called. Its
243 * <code>onDeregistration</code> method will be called each time
244 * it is deregistered from a category, for example if a
245 * category is removed or the registry is garbage collected.
246 *
247 * @param provider the service provide object to be registered.
248 * @param category the category under which to register the
249 * provider.
250 *
251 * @return true if no provider of the same class was previously
252 * registered in the same category category.
253 *
254 * @exception IllegalArgumentException if <code>provider</code> is
255 * <code>null</code>.
256 * @exception IllegalArgumentException if there is no category
257 * corresponding to <code>category</code>.
258 * @exception ClassCastException if provider does not implement
259 * the <code>Class</code> defined by <code>category</code>.
260 */
261 public <T> boolean registerServiceProvider(T provider,
262 Class<T> category) {
263 if (provider == null) {
264 throw new IllegalArgumentException("provider == null!");
265 }
266 SubRegistry reg = (SubRegistry)categoryMap.get(category);
267 if (reg == null) {
268 throw new IllegalArgumentException("category unknown!");
269 }
270 if (!category.isAssignableFrom(provider.getClass())) {
271 throw new ClassCastException();
272 }
273
274 return reg.registerServiceProvider(provider);
275 }
276
277 /**
278 * Adds a service provider object to the registry. The provider
279 * is associated within each category present in the registry
280 * whose <code>Class</code> it implements.
281 *
282 * <p> If <code>provider</code> implements the
283 * <code>RegisterableService</code> interface, its
284 * <code>onRegistration</code> method will be called once for each
285 * category it is registered under. Its
286 * <code>onDeregistration</code> method will be called each time
287 * it is deregistered from a category or when the registry is
288 * finalized.
289 *
290 * @param provider the service provider object to be registered.
291 *
292 * @exception IllegalArgumentException if
293 * <code>provider</code> is <code>null</code>.
294 */
295 public void registerServiceProvider(Object provider) {
296 if (provider == null) {
297 throw new IllegalArgumentException("provider == null!");
298 }
299 Iterator regs = getSubRegistries(provider);
300 while (regs.hasNext()) {
301 SubRegistry reg = (SubRegistry)regs.next();
302 reg.registerServiceProvider(provider);
303 }
304 }
305
306 /**
307 * Adds a set of service provider objects, taken from an
308 * <code>Iterator</code> to the registry. Each provider is
309 * associated within each category present in the registry whose
310 * <code>Class</code> it implements.
311 *
312 * <p> For each entry of <code>providers</code> that implements
313 * the <code>RegisterableService</code> interface, its
314 * <code>onRegistration</code> method will be called once for each
315 * category it is registered under. Its
316 * <code>onDeregistration</code> method will be called each time
317 * it is deregistered from a category or when the registry is
318 * finalized.
319 *
320 * @param providers an Iterator containing service provider
321 * objects to be registered.
322 *
323 * @exception IllegalArgumentException if <code>providers</code>
324 * is <code>null</code> or contains a <code>null</code> entry.
325 */
326 public void registerServiceProviders(Iterator<?> providers) {
327 if (providers == null) {
328 throw new IllegalArgumentException("provider == null!");
329 }
330 while (providers.hasNext()) {
331 registerServiceProvider(providers.next());
332 }
333 }
334
335 /**
336 * Removes a service provider object from the given category. If
337 * the provider was not previously registered, nothing happens and
338 * <code>false</code> is returned. Otherwise, <code>true</code>
339 * is returned. If an object of the same class as
340 * <code>provider</code> but not equal (using <code>==</code>) to
341 * <code>provider</code> is registered, it will not be
342 * deregistered.
343 *
344 * <p> If <code>provider</code> implements the
345 * <code>RegisterableService</code> interface, its
346 * <code>onDeregistration</code> method will be called.
347 *
348 * @param provider the service provider object to be deregistered.
349 * @param category the category from which to deregister the
350 * provider.
351 *
352 * @return <code>true</code> if the provider was previously
353 * registered in the same category category,
354 * <code>false</code> otherwise.
355 *
356 * @exception IllegalArgumentException if <code>provider</code> is
357 * <code>null</code>.
358 * @exception IllegalArgumentException if there is no category
359 * corresponding to <code>category</code>.
360 * @exception ClassCastException if provider does not implement
361 * the class defined by <code>category</code>.
362 */
363 public <T> boolean deregisterServiceProvider(T provider,
364 Class<T> category) {
365 if (provider == null) {
366 throw new IllegalArgumentException("provider == null!");
367 }
368 SubRegistry reg = (SubRegistry)categoryMap.get(category);
369 if (reg == null) {
370 throw new IllegalArgumentException("category unknown!");
371 }
372 if (!category.isAssignableFrom(provider.getClass())) {
373 throw new ClassCastException();
374 }
375 return reg.deregisterServiceProvider(provider);
376 }
377
378 /**
379 * Removes a service provider object from all categories that
380 * contain it.
381 *
382 * @param provider the service provider object to be deregistered.
383 *
384 * @exception IllegalArgumentException if <code>provider</code> is
385 * <code>null</code>.
386 */
387 public void deregisterServiceProvider(Object provider) {
388 if (provider == null) {
389 throw new IllegalArgumentException("provider == null!");
390 }
391 Iterator regs = getSubRegistries(provider);
392 while (regs.hasNext()) {
393 SubRegistry reg = (SubRegistry)regs.next();
394 reg.deregisterServiceProvider(provider);
395 }
396 }
397
398 /**
399 * Returns <code>true</code> if <code>provider</code> is currently
400 * registered.
401 *
402 * @param provider the service provider object to be queried.
403 *
404 * @return <code>true</code> if the given provider has been
405 * registered.
406 *
407 * @exception IllegalArgumentException if <code>provider</code> is
408 * <code>null</code>.
409 */
410 public boolean contains(Object provider) {
411 if (provider == null) {
412 throw new IllegalArgumentException("provider == null!");
413 }
414 Iterator regs = getSubRegistries(provider);
415 while (regs.hasNext()) {
416 SubRegistry reg = (SubRegistry)regs.next();
417 if (reg.contains(provider)) {
418 return true;
419 }
420 }
421
422 return false;
423 }
424
425 /**
426 * Returns an <code>Iterator</code> containing all registered
427 * service providers in the given category. If
428 * <code>useOrdering</code> is <code>false</code>, the iterator
429 * will return all of the server provider objects in an arbitrary
430 * order. Otherwise, the ordering will respect any pairwise
431 * orderings that have been set. If the graph of pairwise
432 * orderings contains cycles, any providers that belong to a cycle
433 * will not be returned.
434 *
435 * @param category the category to be retrieved from.
436 * @param useOrdering <code>true</code> if pairwise orderings
437 * should be taken account in ordering the returned objects.
438 *
439 * @return an <code>Iterator</code> containing service provider
440 * objects from the given category, possibly in order.
441 *
442 * @exception IllegalArgumentException if there is no category
443 * corresponding to <code>category</code>.
444 */
445 public <T> Iterator<T> getServiceProviders(Class<T> category,
446 boolean useOrdering) {
447 SubRegistry reg = (SubRegistry)categoryMap.get(category);
448 if (reg == null) {
449 throw new IllegalArgumentException("category unknown!");
450 }
451 return reg.getServiceProviders(useOrdering);
452 }
453
454 /**
455 * A simple filter interface used by
456 * <code>ServiceRegistry.getServiceProviders</code> to select
457 * providers matching an arbitrary criterion. Classes that
458 * implement this interface should be defined in order to make use
459 * of the <code>getServiceProviders</code> method of
460 * <code>ServiceRegistry</code> that takes a <code>Filter</code>.
461 *
462 * @see ServiceRegistry#getServiceProviders(Class, ServiceRegistry.Filter, boolean)
463 */
464 public interface Filter {
465
466 /**
467 * Returns <code>true</code> if the given
468 * <code>provider</code> object matches the criterion defined
469 * by this <code>Filter</code>.
470 *
471 * @param provider a service provider <code>Object</code>.
472 *
473 * @return true if the provider matches the criterion.
474 */
475 boolean filter(Object provider);
476 }
477
478 /**
479 * Returns an <code>Iterator</code> containing service provider
480 * objects within a given category that satisfy a criterion
481 * imposed by the supplied <code>ServiceRegistry.Filter</code>
482 * object's <code>filter</code> method.
483 *
484 * <p> The <code>useOrdering</code> argument controls the
485 * ordering of the results using the same rules as
486 * <code>getServiceProviders(Class, boolean)</code>.
487 *
488 * @param category the category to be retrieved from.
489 * @param filter an instance of <code>ServiceRegistry.Filter</code>
490 * whose <code>filter</code> method will be invoked.
491 * @param useOrdering <code>true</code> if pairwise orderings
492 * should be taken account in ordering the returned objects.
493 *
494 * @return an <code>Iterator</code> containing service provider
495 * objects from the given category, possibly in order.
496 *
497 * @exception IllegalArgumentException if there is no category
498 * corresponding to <code>category</code>.
499 */
500 public <T> Iterator<T> getServiceProviders(Class<T> category,
501 Filter filter,
502 boolean useOrdering) {
503 SubRegistry reg = (SubRegistry)categoryMap.get(category);
504 if (reg == null) {
505 throw new IllegalArgumentException("category unknown!");
506 }
507 Iterator iter = getServiceProviders(category, useOrdering);
508 return new FilterIterator(iter, filter);
509 }
510
511 /**
512 * Returns the currently registered service provider object that
513 * is of the given class type. At most one object of a given
514 * class is allowed to be registered at any given time. If no
515 * registered object has the desired class type, <code>null</code>
516 * is returned.
517 *
518 * @param providerClass the <code>Class</code> of the desired
519 * service provider object.
520 *
521 * @return a currently registered service provider object with the
522 * desired <code>Class</code>type, or <code>null</code> is none is
523 * present.
524 *
525 * @exception IllegalArgumentException if <code>providerClass</code> is
526 * <code>null</code>.
527 */
528 public <T> T getServiceProviderByClass(Class<T> providerClass) {
529 if (providerClass == null) {
530 throw new IllegalArgumentException("providerClass == null!");
531 }
532 Iterator iter = categoryMap.keySet().iterator();
533 while (iter.hasNext()) {
534 Class c = (Class)iter.next();
535 if (c.isAssignableFrom(providerClass)) {
536 SubRegistry reg = (SubRegistry)categoryMap.get(c);
537 T provider = reg.getServiceProviderByClass(providerClass);
538 if (provider != null) {
539 return provider;
540 }
541 }
542 }
543 return null;
544 }
545
546 /**
547 * Sets a pairwise ordering between two service provider objects
548 * within a given category. If one or both objects are not
549 * currently registered within the given category, or if the
550 * desired ordering is already set, nothing happens and
551 * <code>false</code> is returned. If the providers previously
552 * were ordered in the reverse direction, that ordering is
553 * removed.
554 *
555 * <p> The ordering will be used by the
556 * <code>getServiceProviders</code> methods when their
557 * <code>useOrdering</code> argument is <code>true</code>.
558 *
559 * @param category a <code>Class</code> object indicating the
560 * category under which the preference is to be established.
561 * @param firstProvider the preferred provider.
562 * @param secondProvider the provider to which
563 * <code>firstProvider</code> is preferred.
564 *
565 * @return <code>true</code> if a previously unset ordering
566 * was established.
567 *
568 * @exception IllegalArgumentException if either provider is
569 * <code>null</code> or they are the same object.
570 * @exception IllegalArgumentException if there is no category
571 * corresponding to <code>category</code>.
572 */
573 public <T> boolean setOrdering(Class<T> category,
574 T firstProvider,
575 T secondProvider) {
576 if (firstProvider == null || secondProvider == null) {
577 throw new IllegalArgumentException("provider is null!");
578 }
579 if (firstProvider == secondProvider) {
580 throw new IllegalArgumentException("providers are the same!");
581 }
582 SubRegistry reg = (SubRegistry)categoryMap.get(category);
583 if (reg == null) {
584 throw new IllegalArgumentException("category unknown!");
585 }
586 if (reg.contains(firstProvider) &&
587 reg.contains(secondProvider)) {
588 return reg.setOrdering(firstProvider, secondProvider);
589 }
590 return false;
591 }
592
593 /**
594 * Sets a pairwise ordering between two service provider objects
595 * within a given category. If one or both objects are not
596 * currently registered within the given category, or if no
597 * ordering is currently set between them, nothing happens
598 * and <code>false</code> is returned.
599 *
600 * <p> The ordering will be used by the
601 * <code>getServiceProviders</code> methods when their
602 * <code>useOrdering</code> argument is <code>true</code>.
603 *
604 * @param category a <code>Class</code> object indicating the
605 * category under which the preference is to be disestablished.
606 * @param firstProvider the formerly preferred provider.
607 * @param secondProvider the provider to which
608 * <code>firstProvider</code> was formerly preferred.
609 *
610 * @return <code>true</code> if a previously set ordering was
611 * disestablished.
612 *
613 * @exception IllegalArgumentException if either provider is
614 * <code>null</code> or they are the same object.
615 * @exception IllegalArgumentException if there is no category
616 * corresponding to <code>category</code>.
617 */
618 public <T> boolean unsetOrdering(Class<T> category,
619 T firstProvider,
620 T secondProvider) {
621 if (firstProvider == null || secondProvider == null) {
622 throw new IllegalArgumentException("provider is null!");
623 }
624 if (firstProvider == secondProvider) {
625 throw new IllegalArgumentException("providers are the same!");
626 }
627 SubRegistry reg = (SubRegistry)categoryMap.get(category);
628 if (reg == null) {
629 throw new IllegalArgumentException("category unknown!");
630 }
631 if (reg.contains(firstProvider) &&
632 reg.contains(secondProvider)) {
633 return reg.unsetOrdering(firstProvider, secondProvider);
634 }
635 return false;
636 }
637
638 /**
639 * Deregisters all service provider object currently registered
640 * under the given category.
641 *
642 * @param category the category to be emptied.
643 *
644 * @exception IllegalArgumentException if there is no category
645 * corresponding to <code>category</code>.
646 */
647 public void deregisterAll(Class<?> category) {
648 SubRegistry reg = (SubRegistry)categoryMap.get(category);
649 if (reg == null) {
650 throw new IllegalArgumentException("category unknown!");
651 }
652 reg.clear();
653 }
654
655 /**
656 * Deregisters all currently registered service providers from all
657 * categories.
658 */
659 public void deregisterAll() {
660 Iterator iter = categoryMap.values().iterator();
661 while (iter.hasNext()) {
662 SubRegistry reg = (SubRegistry)iter.next();
663 reg.clear();
664 }
665 }
666
667 /**
668 * Finalizes this object prior to garbage collection. The
669 * <code>deregisterAll</code> method is called to deregister all
670 * currently registered service providers. This method should not
671 * be called from application code.
672 *
673 * @exception Throwable if an error occurs during superclass
674 * finalization.
675 */
676 public void finalize() throws Throwable {
677 deregisterAll();
678 super.finalize();
679 }
680 }
681
682
683 /**
684 * A portion of a registry dealing with a single superclass or
685 * interface.
686 */
687 class SubRegistry {
688
689 ServiceRegistry registry;
690
691 Class category;
692
693 // Provider Objects organized by partial oridering
694 PartiallyOrderedSet poset = new PartiallyOrderedSet();
695
696 // Class -> Provider Object of that class
697 Map<Class<?>,Object> map = new HashMap();
698
699 public SubRegistry(ServiceRegistry registry, Class category) {
700 this.registry = registry;
701 this.category = category;
702 }
703
704 public boolean registerServiceProvider(Object provider) {
705 Object oprovider = map.get(provider.getClass());
706 boolean present = oprovider != null;
707
708 if (present) {
709 deregisterServiceProvider(oprovider);
710 }
711 map.put(provider.getClass(), provider);
712 poset.add(provider);
713 if (provider instanceof RegisterableService) {
714 RegisterableService rs = (RegisterableService)provider;
715 rs.onRegistration(registry, category);
716 }
717
718 return !present;
719 }
720
721 /**
722 * If the provider was not previously registered, do nothing.
723 *
724 * @return true if the provider was previously registered.
725 */
726 public boolean deregisterServiceProvider(Object provider) {
727 Object oprovider = map.get(provider.getClass());
728
729 if (provider == oprovider) {
730 map.remove(provider.getClass());
731 poset.remove(provider);
732 if (provider instanceof RegisterableService) {
733 RegisterableService rs = (RegisterableService)provider;
734 rs.onDeregistration(registry, category);
735 }
736
737 return true;
738 }
739 return false;
740 }
741
742 public boolean contains(Object provider) {
743 Object oprovider = map.get(provider.getClass());
744 return oprovider == provider;
745 }
746
747 public boolean setOrdering(Object firstProvider,
748 Object secondProvider) {
749 return poset.setOrdering(firstProvider, secondProvider);
750 }
751
752 public boolean unsetOrdering(Object firstProvider,
753 Object secondProvider) {
754 return poset.unsetOrdering(firstProvider, secondProvider);
755 }
756
757 public Iterator getServiceProviders(boolean useOrdering) {
758 if (useOrdering) {
759 return poset.iterator();
760 } else {
761 return map.values().iterator();
762 }
763 }
764
765 public <T> T getServiceProviderByClass(Class<T> providerClass) {
766 return (T)map.get(providerClass);
767 }
768
769 public void clear() {
770 Iterator iter = map.values().iterator();
771 while (iter.hasNext()) {
772 Object provider = iter.next();
773 iter.remove();
774
775 if (provider instanceof RegisterableService) {
776 RegisterableService rs = (RegisterableService)provider;
777 rs.onDeregistration(registry, category);
778 }
779 }
780 poset.clear();
781 }
782
783 public void finalize() {
784 clear();
785 }
786 }
787
788
789 /**
790 * A class for wrapping <code>Iterators</code> with a filter function.
791 * This provides an iterator for a subset without duplication.
792 */
793 class FilterIterator<T> implements Iterator<T> {
794
795 private Iterator<T> iter;
796 private ServiceRegistry.Filter filter;
797
798 private T next = null;
799
800 public FilterIterator(Iterator<T> iter,
801 ServiceRegistry.Filter filter) {
802 this.iter = iter;
803 this.filter = filter;
804 advance();
805 }
806
807 private void advance() {
808 while (iter.hasNext()) {
809 T elt = iter.next();
810 if (filter.filter(elt)) {
811 next = elt;
812 return;
813 }
814 }
815
816 next = null;
817 }
818
819 public boolean hasNext() {
820 return next != null;
821 }
822
823 public T next() {
824 if (next == null) {
825 throw new NoSuchElementException();
826 }
827 T o = next;
828 advance();
829 return o;
830 }
831
832 public void remove() {
833 throw new UnsupportedOperationException();
834 }
835 }
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