ZoneRulesProvider.java
/*
* Copyright (c) 2007-present, Stephen Colebourne & Michael Nascimento Santos
*
* All rights reserved.
*
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* modification, are permitted provided that the following conditions are met:
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* this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
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*
* * Neither the name of JSR-310 nor the names of its contributors
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*
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package org.threeten.bp.zone;
import java.util.Collections;
import java.util.NavigableMap;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CopyOnWriteArrayList;
import org.threeten.bp.DateTimeException;
import org.threeten.bp.ZoneId;
import org.threeten.bp.ZonedDateTime;
import org.threeten.bp.jdk8.Jdk8Methods;
/**
* Provider of time-zone rules to the system.
* <p>
* This class manages the configuration of time-zone rules.
* The static methods provide the public API that can be used to manage the providers.
* The abstract methods provide the SPI that allows rules to be provided.
* <p>
* Rules are looked up primarily by zone ID, as used by {@link ZoneId}.
* Only zone region IDs may be used, zone offset IDs are not used here.
* <p>
* Time-zone rules are political, thus the data can change at any time.
* Each provider will provide the latest rules for each zone ID, but they
* may also provide the history of how the rules changed.
*
* <h3>Specification for implementors</h3>
* This interface is a service provider that can be called by multiple threads.
* Implementations must be immutable and thread-safe.
* <p>
* Providers must ensure that once a rule has been seen by the application, the
* rule must continue to be available.
* <p>
* Many systems would like to update time-zone rules dynamically without stopping the JVM.
* When examined in detail, this is a complex problem.
* Providers may choose to handle dynamic updates, however the default provider does not.
*/
public abstract class ZoneRulesProvider {
/**
* The set of loaded providers.
*/
private static final CopyOnWriteArrayList<ZoneRulesProvider> PROVIDERS = new CopyOnWriteArrayList<ZoneRulesProvider>();
/**
* The lookup from zone region ID to provider.
*/
private static final ConcurrentMap<String, ZoneRulesProvider> ZONES = new ConcurrentHashMap<String, ZoneRulesProvider>(512, 0.75f, 2);
static {
ZoneRulesInitializer.initialize();
}
//-------------------------------------------------------------------------
/**
* Gets the set of available zone IDs.
* <p>
* These zone IDs are loaded and available for use by {@code ZoneId}.
*
* @return the unmodifiable set of zone IDs, not null
*/
public static Set<String> getAvailableZoneIds() {
return Collections.unmodifiableSet(ZONES.keySet());
}
/**
* Gets the rules for the zone ID.
* <p>
* This returns the latest available rules for the zone ID.
* <p>
* This method relies on time-zone data provider files that are configured.
* These are loaded using a {@code ServiceLoader}.
* <p>
* The caching flag is designed to allow provider implementations to
* prevent the rules being cached in {@code ZoneId}.
* Under normal circumstances, the caching of zone rules is highly desirable
* as it will provide greater performance. However, there is a use case where
* the caching would not be desirable, see {@link #provideRules}.
*
* @param zoneId the zone ID as defined by {@code ZoneId}, not null
* @param forCaching whether the rules are being queried for caching,
* true if the returned rules will be cached by {@code ZoneId},
* false if they will be returned to the user without being cached in {@code ZoneId}
* @return the rules, null if {@code forCaching} is true and this
* is a dynamic provider that wants to prevent caching in {@code ZoneId},
* otherwise not null
* @throws ZoneRulesException if rules cannot be obtained for the zone ID
*/
public static ZoneRules getRules(String zoneId, boolean forCaching) {
Jdk8Methods.requireNonNull(zoneId, "zoneId");
return getProvider(zoneId).provideRules(zoneId, forCaching);
}
/**
* Gets the history of rules for the zone ID.
* <p>
* Time-zones are defined by governments and change frequently.
* This method allows applications to find the history of changes to the
* rules for a single zone ID. The map is keyed by a string, which is the
* version string associated with the rules.
* <p>
* The exact meaning and format of the version is provider specific.
* The version must follow lexicographical order, thus the returned map will
* be order from the oldest known rules to the newest available rules.
* The default 'TZDB' group uses version numbering consisting of the year
* followed by a letter, such as '2009e' or '2012f'.
* <p>
* Implementations must provide a result for each valid zone ID, however
* they do not have to provide a history of rules.
* Thus the map will always contain one element, and will only contain more
* than one element if historical rule information is available.
*
* @param zoneId the zone region ID as used by {@code ZoneId}, not null
* @return a modifiable copy of the history of the rules for the ID, sorted
* from oldest to newest, not null
* @throws ZoneRulesException if history cannot be obtained for the zone ID
*/
public static NavigableMap<String, ZoneRules> getVersions(String zoneId) {
Jdk8Methods.requireNonNull(zoneId, "zoneId");
return getProvider(zoneId).provideVersions(zoneId);
}
/**
* Gets the provider for the zone ID.
*
* @param zoneId the zone region ID as used by {@code ZoneId}, not null
* @return the provider, not null
* @throws ZoneRulesException if the zone ID is unknown
*/
private static ZoneRulesProvider getProvider(String zoneId) {
ZoneRulesProvider provider = ZONES.get(zoneId);
if (provider == null) {
if (ZONES.isEmpty()) {
throw new ZoneRulesException("No time-zone data files registered");
}
throw new ZoneRulesException("Unknown time-zone ID: " + zoneId);
}
return provider;
}
//-------------------------------------------------------------------------
/**
* Registers a zone rules provider.
* <p>
* This adds a new provider to those currently available.
* A provider supplies rules for one or more zone IDs.
* A provider cannot be registered if it supplies a zone ID that has already been
* registered. See the notes on time-zone IDs in {@link ZoneId}, especially
* the section on using the concept of a "group" to make IDs unique.
* <p>
* To ensure the integrity of time-zones already created, there is no way
* to deregister providers.
*
* @param provider the provider to register, not null
* @throws ZoneRulesException if a region is already registered
*/
public static void registerProvider(ZoneRulesProvider provider) {
Jdk8Methods.requireNonNull(provider, "provider");
registerProvider0(provider);
PROVIDERS.add(provider);
}
/**
* Registers the provider.
*
* @param provider the provider to register, not null
* @throws ZoneRulesException if unable to complete the registration
*/
private static void registerProvider0(ZoneRulesProvider provider) {
for (String zoneId : provider.provideZoneIds()) {
Jdk8Methods.requireNonNull(zoneId, "zoneId");
ZoneRulesProvider old = ZONES.putIfAbsent(zoneId, provider);
if (old != null) {
throw new ZoneRulesException(
"Unable to register zone as one already registered with that ID: " + zoneId +
", currently loading from provider: " + provider);
}
}
}
//-------------------------------------------------------------------------
/**
* Refreshes the rules from the underlying data provider.
* <p>
* This method is an extension point that allows providers to refresh their
* rules dynamically at a time of the applications choosing.
* After calling this method, the offset stored in any {@link ZonedDateTime}
* may be invalid for the zone ID.
* <p>
* Dynamic behavior is entirely optional and most providers, including the
* default provider, do not support it.
*
* @return true if the rules were updated
* @throws ZoneRulesException if an error occurs during the refresh
*/
public static boolean refresh() {
boolean changed = false;
for (ZoneRulesProvider provider : PROVIDERS) {
changed |= provider.provideRefresh();
}
return changed;
}
//-----------------------------------------------------------------------
/**
* Constructor.
*/
protected ZoneRulesProvider() {
}
//-----------------------------------------------------------------------
/**
* SPI method to get the available zone IDs.
* <p>
* This obtains the IDs that this {@code ZoneRulesProvider} provides.
* A provider should provide data for at least one region.
* <p>
* The returned regions remain available and valid for the lifetime of the application.
* A dynamic provider may increase the set of regions as more data becomes available.
*
* @return the unmodifiable set of region IDs being provided, not null
* @throws ZoneRulesException if a problem occurs while providing the IDs
*/
protected abstract Set<String> provideZoneIds();
/**
* SPI method to get the rules for the zone ID.
* <p>
* This loads the rules for the region and version specified.
* The version may be null to indicate the "latest" version.
*
* @param regionId the time-zone region ID, not null
* @return the rules, not null
* @throws DateTimeException if rules cannot be obtained
*/
protected abstract ZoneRules provideRules(String regionId, boolean forCaching);
/**
* SPI method to get the history of rules for the zone ID.
* <p>
* This returns a map of historical rules keyed by a version string.
* The exact meaning and format of the version is provider specific.
* The version must follow lexicographical order, thus the returned map will
* be order from the oldest known rules to the newest available rules.
* The default 'TZDB' group uses version numbering consisting of the year
* followed by a letter, such as '2009e' or '2012f'.
* <p>
* Implementations must provide a result for each valid zone ID, however
* they do not have to provide a history of rules.
* Thus the map will always contain one element, and will only contain more
* than one element if historical rule information is available.
* <p>
* The returned versions remain available and valid for the lifetime of the application.
* A dynamic provider may increase the set of versions as more data becomes available.
*
* @param zoneId the zone region ID as used by {@code ZoneId}, not null
* @return a modifiable copy of the history of the rules for the ID, sorted
* from oldest to newest, not null
* @throws ZoneRulesException if history cannot be obtained for the zone ID
*/
protected abstract NavigableMap<String, ZoneRules> provideVersions(String zoneId);
/**
* SPI method to refresh the rules from the underlying data provider.
* <p>
* This method provides the opportunity for a provider to dynamically
* recheck the underlying data provider to find the latest rules.
* This could be used to load new rules without stopping the JVM.
* Dynamic behavior is entirely optional and most providers do not support it.
* <p>
* This implementation returns false.
*
* @return true if the rules were updated
* @throws DateTimeException if an error occurs during the refresh
*/
protected boolean provideRefresh() {
return false;
}
}