* 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. *
* ZoneRulesProvider may be installed in an instance of the Java Platform as * extension classes, that is, jar files placed into any of the usual extension * directories. Installed providers are loaded using the service-provider loading * facility defined by the {@link ServiceLoader} class. A ZoneRulesProvider * identifies itself with a provider configuration file named * {@code java.time.zone.ZoneRulesProvider} in the resource directory * {@code META-INF/services}. The file should contain a line that specifies the * fully qualified concrete zonerules-provider class name. * Providers may also be made available by adding them to the class path or by * registering themselves via {@link #registerProvider} method. *
* The Java virtual machine has a default provider that provides zone rules * for the time-zones defined by IANA Time Zone Database (TZDB). If the system * property {@code java.time.zone.DefaultZoneRulesProvider} is defined then * it is taken to be the fully-qualified name of a concrete ZoneRulesProvider * class to be loaded as the default provider, using the system class loader. * If this system property is not defined, a system-default provider will be * loaded to serve as the default provider. *
* 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. *
* 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. * *
* Providers must ensure that once a rule has been seen by the application, the * rule must continue to be available. *
* Providers are encouraged to implement a meaningful {@code toString} method. *
* 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.
*
* @since 1.8
*/
public abstract class ZoneRulesProvider {
/**
* The set of loaded providers.
*/
private static final CopyOnWriteArrayList
* These IDs are the string form of a {@link ZoneId}.
*
* @return a modifiable copy of the set of zone IDs, not null
*/
public static Set
* This returns the latest available rules for the zone ID.
*
* This method relies on time-zone data provider files that are configured.
* These are loaded using a {@code ServiceLoader}.
*
* 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) {
Objects.requireNonNull(zoneId, "zoneId");
return getProvider(zoneId).provideRules(zoneId, forCaching);
}
/**
* Gets the history of rules for the zone ID.
*
* 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.
*
* 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'.
*
* 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 ID as defined 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
* 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.
*
* 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 zone ID is already registered
*/
public static void registerProvider(ZoneRulesProvider provider) {
Objects.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()) {
Objects.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.
*
* This method allows an application to request that the providers check
* for any updates to the provided rules.
* After calling this method, the offset stored in any {@link ZonedDateTime}
* may be invalid for the zone ID.
*
* Dynamic update of rules is a complex problem and most applications
* should not use this method or dynamic rules.
* To achieve dynamic rules, a provider implementation will have to be written
* as per the specification of this class.
* In addition, instances of {@code ZoneRules} must not be cached in the
* application as they will become stale. However, the boolean flag on
* {@link #provideRules(String, boolean)} allows provider implementations
* to control the caching of {@code ZoneId}, potentially ensuring that
* all objects in the system see the new rules.
* Note that there is likely to be a cost in performance of a dynamic rules
* provider. Note also that no dynamic rules provider is in this specification.
*
* @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.
*
* This obtains the IDs that this {@code ZoneRulesProvider} provides.
* A provider should provide data for at least one zone ID.
*
* The returned zone IDs remain available and valid for the lifetime of the application.
* A dynamic provider may increase the set of IDs as more data becomes available.
*
* @return the set of zone IDs being provided, not null
* @throws ZoneRulesException if a problem occurs while providing the IDs
*/
protected abstract Set
* This loads the rules for the specified zone ID.
* The provider implementation must validate that the zone ID is valid and
* available, throwing a {@code ZoneRulesException} if it is not.
* The result of the method in the valid case depends on the caching flag.
*
* If the provider implementation is not dynamic, then the result of the
* method must be the non-null set of rules selected by the ID.
*
* If the provider implementation is dynamic, then the flag gives the option
* of preventing the returned rules from being cached in {@link ZoneId}.
* When the flag is true, the provider is permitted to return null, where
* null will prevent the rules from being cached in {@code ZoneId}.
* When the flag is false, the provider must return non-null rules.
*
* @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
*/
protected abstract ZoneRules provideRules(String zoneId, boolean forCaching);
/**
* SPI method to get the history of rules for the zone ID.
*
* 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'.
*
* 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 contain at least one element, and will only contain
* more than one element if historical rule information is available.
*
* 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 ID as defined 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
* 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.
*
* This implementation returns false.
*
* @return true if the rules were updated
* @throws ZoneRulesException if an error occurs during the refresh
*/
protected boolean provideRefresh() {
return false;
}
}