org.threeten.bp.zone
Class ZoneRulesProvider

java.lang.Object
  org.threeten.bp.zone.ZoneRulesProvider

Direct Known Subclasses:

TzdbZoneRulesProvider

public abstract class ZoneRulesProvider
extends Object

Provider of time-zone rules to the system.

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.

Rules are looked up primarily by zone ID, as used by 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.

Specification for implementors

Providers must ensure that once a rule has been seen by the application, the rule must continue to be available.

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.

ZoneRulesProvider

protected ZoneRulesProvider()

Constructor.

getAvailableZoneIds

public static Set<String> getAvailableZoneIds()

Gets the set of available zone IDs.

These zone IDs are loaded and available for use by ZoneId.

Returns:

a modifiable copy of the set of zone IDs, not null

getRules

public static ZoneRules getRules(String zoneId,
                                 boolean forCaching)

Gets the rules for the zone ID.

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 ServiceLoader.

The caching flag is designed to allow provider implementations to prevent the rules being cached in 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 provideRules(java.lang.String, boolean).

Parameters:

zoneId - the zone ID as defined by ZoneId, not null

forCaching - whether the rules are being queried for caching, true if the returned rules will be cached by ZoneId, false if they will be returned to the user without being cached in ZoneId

Returns:

the rules, null if forCaching is true and this is a dynamic provider that wants to prevent caching in ZoneId, otherwise not null

Throws:

ZoneRulesException - if rules cannot be obtained for the zone ID

getVersions

public static NavigableMap<String,ZoneRules> getVersions(String zoneId)

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.

Parameters:

zoneId - the zone region ID as used by ZoneId, not null

Returns:

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

registerProvider

public static void registerProvider(ZoneRulesProvider provider)

Registers a zone rules provider.

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 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.

Parameters:

provider - the provider to register, not null

Throws:

ZoneRulesException - if a region is already registered

refresh

public static boolean refresh()

Refreshes the rules from the underlying data provider.

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 ZonedDateTime may be invalid for the zone ID.

Dynamic behavior is entirely optional and most providers, including the default provider, do not support it.

Returns:

true if the rules were updated

Throws:

ZoneRulesException - if an error occurs during the refresh

provideZoneIds

protected abstract Set<String> provideZoneIds()

SPI method to get the available zone IDs.

This obtains the IDs that this ZoneRulesProvider provides. A provider should provide data for at least one region.

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.

Returns:

the unmodifiable set of region IDs being provided, not null

Throws:

ZoneRulesException - if a problem occurs while providing the IDs

provideRules

protected abstract ZoneRules provideRules(String regionId,
                                          boolean forCaching)

SPI method to get the rules for the zone ID.

This loads the rules for the region and version specified. The version may be null to indicate the "latest" version.

Parameters:

regionId - the time-zone region ID, not null

Returns:

the rules, not null

Throws:

DateTimeException - if rules cannot be obtained

provideVersions

protected abstract NavigableMap<String,ZoneRules> provideVersions(String zoneId)

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 always contain 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.

Parameters:

zoneId - the zone region ID as used by ZoneId, not null

Returns:

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

provideRefresh

protected boolean provideRefresh()

SPI method to refresh the rules from the underlying data provider.

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.

Returns:

true if the rules were updated

Throws:

DateTimeException - if an error occurs during the refresh