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25
26/*
27 * This file is available under and governed by the GNU General Public
28 * License version 2 only, as published by the Free Software Foundation.
29 * However, the following notice accompanied the original version of this
30 * file:
31 *
32 * Copyright (c) 2009-2012, Stephen Colebourne & Michael Nascimento Santos
33 *
34 * All rights reserved.
35 *
36 * Redistribution and use in source and binary forms, with or without
37 * modification, are permitted provided that the following conditions are met:
38 *
39 *  * Redistributions of source code must retain the above copyright notice,
40 *    this list of conditions and the following disclaimer.
41 *
42 *  * Redistributions in binary form must reproduce the above copyright notice,
43 *    this list of conditions and the following disclaimer in the documentation
44 *    and/or other materials provided with the distribution.
45 *
46 *  * Neither the name of JSR-310 nor the names of its contributors
47 *    may be used to endorse or promote products derived from this software
48 *    without specific prior written permission.
49 *
50 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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61 */
62package java.time.zone;
63
64import java.security.AccessController;
65import java.security.PrivilegedAction;
66import java.time.ZoneId;
67import java.time.ZonedDateTime;
68import java.util.ArrayList;
69import java.util.HashSet;
70import java.util.Iterator;
71import java.util.List;
72import java.util.NavigableMap;
73import java.util.Objects;
74import java.util.ServiceConfigurationError;
75import java.util.ServiceLoader;
76import java.util.Set;
77import java.util.concurrent.ConcurrentHashMap;
78import java.util.concurrent.ConcurrentMap;
79import java.util.concurrent.CopyOnWriteArrayList;
80import java.util.Collections;
81
82/**
83 * Provider of time-zone rules to the system.
84 * <p>
85 * This class manages the configuration of time-zone rules.
86 * The static methods provide the public API that can be used to manage the providers.
87 * The abstract methods provide the SPI that allows rules to be provided.
88 * <p>
89 * ZoneRulesProvider may be installed in an instance of the Java Platform as
90 * extension classes, that is, jar files placed into any of the usual extension
91 * directories. Installed providers are loaded using the service-provider loading
92 * facility defined by the {@link ServiceLoader} class. A ZoneRulesProvider
93 * identifies itself with a provider configuration file named
94 * {@code java.time.zone.ZoneRulesProvider} in the resource directory
95 * {@code META-INF/services}. The file should contain a line that specifies the
96 * fully qualified concrete zonerules-provider class name.
97 * Providers may also be made available by adding them to the class path or by
98 * registering themselves via {@link #registerProvider} method.
99 * <p>
100 * The Java virtual machine has a default provider that provides zone rules
101 * for the time-zones defined by IANA Time Zone Database (TZDB). If the system
102 * property {@code java.time.zone.DefaultZoneRulesProvider} is defined then
103 * it is taken to be the fully-qualified name of a concrete ZoneRulesProvider
104 * class to be loaded as the default provider, using the system class loader.
105 * If this system property is not defined, a system-default provider will be
106 * loaded to serve as the default provider.
107 * <p>
108 * Rules are looked up primarily by zone ID, as used by {@link ZoneId}.
109 * Only zone region IDs may be used, zone offset IDs are not used here.
110 * <p>
111 * Time-zone rules are political, thus the data can change at any time.
112 * Each provider will provide the latest rules for each zone ID, but they
113 * may also provide the history of how the rules changed.
114 *
115 * @implSpec
116 * This interface is a service provider that can be called by multiple threads.
117 * Implementations must be immutable and thread-safe.
118 * <p>
119 * Providers must ensure that once a rule has been seen by the application, the
120 * rule must continue to be available.
121 * <p>
122*  Providers are encouraged to implement a meaningful {@code toString} method.
123 * <p>
124 * Many systems would like to update time-zone rules dynamically without stopping the JVM.
125 * When examined in detail, this is a complex problem.
126 * Providers may choose to handle dynamic updates, however the default provider does not.
127 *
128 * @since 1.8
129 */
130public abstract class ZoneRulesProvider {
131
132    /**
133     * The set of loaded providers.
134     */
135    private static final CopyOnWriteArrayList<ZoneRulesProvider> PROVIDERS = new CopyOnWriteArrayList<>();
136    /**
137     * The lookup from zone ID to provider.
138     */
139    private static final ConcurrentMap<String, ZoneRulesProvider> ZONES = new ConcurrentHashMap<>(512, 0.75f, 2);
140
141    /**
142     * The zone ID data
143     */
144    private static volatile Set<String> ZONE_IDS;
145
146    static {
147        // if the property java.time.zone.DefaultZoneRulesProvider is
148        // set then its value is the class name of the default provider
149        final List<ZoneRulesProvider> loaded = new ArrayList<>();
150        AccessController.doPrivileged(new PrivilegedAction<>() {
151            public Object run() {
152                String prop = System.getProperty("java.time.zone.DefaultZoneRulesProvider");
153                if (prop != null) {
154                    try {
155                        Class<?> c = Class.forName(prop, true, ClassLoader.getSystemClassLoader());
156                        @SuppressWarnings("deprecation")
157                        ZoneRulesProvider provider = ZoneRulesProvider.class.cast(c.newInstance());
158                        registerProvider(provider);
159                        loaded.add(provider);
160                    } catch (Exception x) {
161                        throw new Error(x);
162                    }
163                } else {
164                    registerProvider(new TzdbZoneRulesProvider());
165                }
166                return null;
167            }
168        });
169
170        ServiceLoader<ZoneRulesProvider> sl = ServiceLoader.load(ZoneRulesProvider.class, ClassLoader.getSystemClassLoader());
171        Iterator<ZoneRulesProvider> it = sl.iterator();
172        while (it.hasNext()) {
173            ZoneRulesProvider provider;
174            try {
175                provider = it.next();
176            } catch (ServiceConfigurationError ex) {
177                if (ex.getCause() instanceof SecurityException) {
178                    continue;  // ignore the security exception, try the next provider
179                }
180                throw ex;
181            }
182            boolean found = false;
183            for (ZoneRulesProvider p : loaded) {
184                if (p.getClass() == provider.getClass()) {
185                    found = true;
186                }
187            }
188            if (!found) {
189                registerProvider0(provider);
190                loaded.add(provider);
191            }
192        }
193        // CopyOnWriteList could be slow if lots of providers and each added individually
194        PROVIDERS.addAll(loaded);
195    }
196
197    //-------------------------------------------------------------------------
198    /**
199     * Gets the set of available zone IDs.
200     * <p>
201     * These IDs are the string form of a {@link ZoneId}.
202     *
203     * @return the unmodifiable set of zone IDs, not null
204     */
205    public static Set<String> getAvailableZoneIds() {
206        return ZONE_IDS;
207    }
208
209    /**
210     * Gets the rules for the zone ID.
211     * <p>
212     * This returns the latest available rules for the zone ID.
213     * <p>
214     * This method relies on time-zone data provider files that are configured.
215     * These are loaded using a {@code ServiceLoader}.
216     * <p>
217     * The caching flag is designed to allow provider implementations to
218     * prevent the rules being cached in {@code ZoneId}.
219     * Under normal circumstances, the caching of zone rules is highly desirable
220     * as it will provide greater performance. However, there is a use case where
221     * the caching would not be desirable, see {@link #provideRules}.
222     *
223     * @param zoneId the zone ID as defined by {@code ZoneId}, not null
224     * @param forCaching whether the rules are being queried for caching,
225     * true if the returned rules will be cached by {@code ZoneId},
226     * false if they will be returned to the user without being cached in {@code ZoneId}
227     * @return the rules, null if {@code forCaching} is true and this
228     * is a dynamic provider that wants to prevent caching in {@code ZoneId},
229     * otherwise not null
230     * @throws ZoneRulesException if rules cannot be obtained for the zone ID
231     */
232    public static ZoneRules getRules(String zoneId, boolean forCaching) {
233        Objects.requireNonNull(zoneId, "zoneId");
234        return getProvider(zoneId).provideRules(zoneId, forCaching);
235    }
236
237    /**
238     * Gets the history of rules for the zone ID.
239     * <p>
240     * Time-zones are defined by governments and change frequently.
241     * This method allows applications to find the history of changes to the
242     * rules for a single zone ID. The map is keyed by a string, which is the
243     * version string associated with the rules.
244     * <p>
245     * The exact meaning and format of the version is provider specific.
246     * The version must follow lexicographical order, thus the returned map will
247     * be order from the oldest known rules to the newest available rules.
248     * The default 'TZDB' group uses version numbering consisting of the year
249     * followed by a letter, such as '2009e' or '2012f'.
250     * <p>
251     * Implementations must provide a result for each valid zone ID, however
252     * they do not have to provide a history of rules.
253     * Thus the map will always contain one element, and will only contain more
254     * than one element if historical rule information is available.
255     *
256     * @param zoneId  the zone ID as defined by {@code ZoneId}, not null
257     * @return a modifiable copy of the history of the rules for the ID, sorted
258     *  from oldest to newest, not null
259     * @throws ZoneRulesException if history cannot be obtained for the zone ID
260     */
261    public static NavigableMap<String, ZoneRules> getVersions(String zoneId) {
262        Objects.requireNonNull(zoneId, "zoneId");
263        return getProvider(zoneId).provideVersions(zoneId);
264    }
265
266    /**
267     * Gets the provider for the zone ID.
268     *
269     * @param zoneId  the zone ID as defined by {@code ZoneId}, not null
270     * @return the provider, not null
271     * @throws ZoneRulesException if the zone ID is unknown
272     */
273    private static ZoneRulesProvider getProvider(String zoneId) {
274        ZoneRulesProvider provider = ZONES.get(zoneId);
275        if (provider == null) {
276            if (ZONES.isEmpty()) {
277                throw new ZoneRulesException("No time-zone data files registered");
278            }
279            throw new ZoneRulesException("Unknown time-zone ID: " + zoneId);
280        }
281        return provider;
282    }
283
284    //-------------------------------------------------------------------------
285    /**
286     * Registers a zone rules provider.
287     * <p>
288     * This adds a new provider to those currently available.
289     * A provider supplies rules for one or more zone IDs.
290     * A provider cannot be registered if it supplies a zone ID that has already been
291     * registered. See the notes on time-zone IDs in {@link ZoneId}, especially
292     * the section on using the concept of a "group" to make IDs unique.
293     * <p>
294     * To ensure the integrity of time-zones already created, there is no way
295     * to deregister providers.
296     *
297     * @param provider  the provider to register, not null
298     * @throws ZoneRulesException if a zone ID is already registered
299     */
300    public static void registerProvider(ZoneRulesProvider provider) {
301        Objects.requireNonNull(provider, "provider");
302        registerProvider0(provider);
303        PROVIDERS.add(provider);
304    }
305
306    /**
307     * Registers the provider.
308     *
309     * @param provider  the provider to register, not null
310     * @throws ZoneRulesException if unable to complete the registration
311     */
312    private static synchronized void registerProvider0(ZoneRulesProvider provider) {
313        for (String zoneId : provider.provideZoneIds()) {
314            Objects.requireNonNull(zoneId, "zoneId");
315            ZoneRulesProvider old = ZONES.putIfAbsent(zoneId, provider);
316            if (old != null) {
317                throw new ZoneRulesException(
318                    "Unable to register zone as one already registered with that ID: " + zoneId +
319                    ", currently loading from provider: " + provider);
320            }
321        }
322        Set<String> combinedSet = new HashSet<String>(ZONES.keySet());
323        ZONE_IDS = Collections.unmodifiableSet(combinedSet);
324    }
325
326    /**
327     * Refreshes the rules from the underlying data provider.
328     * <p>
329     * This method allows an application to request that the providers check
330     * for any updates to the provided rules.
331     * After calling this method, the offset stored in any {@link ZonedDateTime}
332     * may be invalid for the zone ID.
333     * <p>
334     * Dynamic update of rules is a complex problem and most applications
335     * should not use this method or dynamic rules.
336     * To achieve dynamic rules, a provider implementation will have to be written
337     * as per the specification of this class.
338     * In addition, instances of {@code ZoneRules} must not be cached in the
339     * application as they will become stale. However, the boolean flag on
340     * {@link #provideRules(String, boolean)} allows provider implementations
341     * to control the caching of {@code ZoneId}, potentially ensuring that
342     * all objects in the system see the new rules.
343     * Note that there is likely to be a cost in performance of a dynamic rules
344     * provider. Note also that no dynamic rules provider is in this specification.
345     *
346     * @return true if the rules were updated
347     * @throws ZoneRulesException if an error occurs during the refresh
348     */
349    public static boolean refresh() {
350        boolean changed = false;
351        for (ZoneRulesProvider provider : PROVIDERS) {
352            changed |= provider.provideRefresh();
353        }
354        return changed;
355    }
356
357    /**
358     * Constructor.
359     */
360    protected ZoneRulesProvider() {
361    }
362
363    //-----------------------------------------------------------------------
364    /**
365     * SPI method to get the available zone IDs.
366     * <p>
367     * This obtains the IDs that this {@code ZoneRulesProvider} provides.
368     * A provider should provide data for at least one zone ID.
369     * <p>
370     * The returned zone IDs remain available and valid for the lifetime of the application.
371     * A dynamic provider may increase the set of IDs as more data becomes available.
372     *
373     * @return the set of zone IDs being provided, not null
374     * @throws ZoneRulesException if a problem occurs while providing the IDs
375     */
376    protected abstract Set<String> provideZoneIds();
377
378    /**
379     * SPI method to get the rules for the zone ID.
380     * <p>
381     * This loads the rules for the specified zone ID.
382     * The provider implementation must validate that the zone ID is valid and
383     * available, throwing a {@code ZoneRulesException} if it is not.
384     * The result of the method in the valid case depends on the caching flag.
385     * <p>
386     * If the provider implementation is not dynamic, then the result of the
387     * method must be the non-null set of rules selected by the ID.
388     * <p>
389     * If the provider implementation is dynamic, then the flag gives the option
390     * of preventing the returned rules from being cached in {@link ZoneId}.
391     * When the flag is true, the provider is permitted to return null, where
392     * null will prevent the rules from being cached in {@code ZoneId}.
393     * When the flag is false, the provider must return non-null rules.
394     *
395     * @param zoneId the zone ID as defined by {@code ZoneId}, not null
396     * @param forCaching whether the rules are being queried for caching,
397     * true if the returned rules will be cached by {@code ZoneId},
398     * false if they will be returned to the user without being cached in {@code ZoneId}
399     * @return the rules, null if {@code forCaching} is true and this
400     * is a dynamic provider that wants to prevent caching in {@code ZoneId},
401     * otherwise not null
402     * @throws ZoneRulesException if rules cannot be obtained for the zone ID
403     */
404    protected abstract ZoneRules provideRules(String zoneId, boolean forCaching);
405
406    /**
407     * SPI method to get the history of rules for the zone ID.
408     * <p>
409     * This returns a map of historical rules keyed by a version string.
410     * The exact meaning and format of the version is provider specific.
411     * The version must follow lexicographical order, thus the returned map will
412     * be order from the oldest known rules to the newest available rules.
413     * The default 'TZDB' group uses version numbering consisting of the year
414     * followed by a letter, such as '2009e' or '2012f'.
415     * <p>
416     * Implementations must provide a result for each valid zone ID, however
417     * they do not have to provide a history of rules.
418     * Thus the map will contain at least one element, and will only contain
419     * more than one element if historical rule information is available.
420     * <p>
421     * The returned versions remain available and valid for the lifetime of the application.
422     * A dynamic provider may increase the set of versions as more data becomes available.
423     *
424     * @param zoneId  the zone ID as defined by {@code ZoneId}, not null
425     * @return a modifiable copy of the history of the rules for the ID, sorted
426     *  from oldest to newest, not null
427     * @throws ZoneRulesException if history cannot be obtained for the zone ID
428     */
429    protected abstract NavigableMap<String, ZoneRules> provideVersions(String zoneId);
430
431    /**
432     * SPI method to refresh the rules from the underlying data provider.
433     * <p>
434     * This method provides the opportunity for a provider to dynamically
435     * recheck the underlying data provider to find the latest rules.
436     * This could be used to load new rules without stopping the JVM.
437     * Dynamic behavior is entirely optional and most providers do not support it.
438     * <p>
439     * This implementation returns false.
440     *
441     * @return true if the rules were updated
442     * @throws ZoneRulesException if an error occurs during the refresh
443     */
444    protected boolean provideRefresh() {
445        return false;
446    }
447
448}
449