Class ZoneId
- All Implemented Interfaces:
Serializable
- Direct Known Subclasses:
ZoneOffset
Europe/Paris
.
A ZoneId
is used to identify the rules used to convert between
an Instant
and a LocalDateTime
.
There are two distinct types of ID:
- Fixed offsets - a fully resolved offset from UTC/Greenwich, that uses the same offset for all local date-times
- Geographical regions - an area where a specific set of rules for finding the offset from UTC/Greenwich apply
ZoneOffset
.
Calling normalized()
on any ZoneId
will ensure that a
fixed offset ID will be represented as a ZoneOffset
.
The actual rules, describing when and how the offset changes, are defined by ZoneRules
.
This class is simply an ID used to obtain the underlying rules.
This approach is taken because rules are defined by governments and change
frequently, whereas the ID is stable.
The distinction has other effects. Serializing the ZoneId
will only send
the ID, whereas serializing the rules sends the entire data set.
Similarly, a comparison of two IDs only examines the ID, whereas
a comparison of two rules examines the entire data set.
Time-zone IDs
The ID is unique within the system. There are three types of ID.
The simplest type of ID is that from ZoneOffset
.
This consists of 'Z' and IDs starting with '+' or '-'.
The next type of ID are offset-style IDs with some form of prefix,
such as 'GMT+2' or 'UTC+01:00'.
The recognised prefixes are 'UTC', 'GMT' and 'UT'.
The offset is the suffix and will be normalized during creation.
These IDs can be normalized to a ZoneOffset
using normalized()
.
The third type of ID are region-based IDs. A region-based ID must be of
two or more characters, and not start with 'UTC', 'GMT', 'UT' '+' or '-'.
Region-based IDs are defined by configuration, see ZoneRulesProvider
.
The configuration focuses on providing the lookup from the ID to the
underlying ZoneRules
.
Time-zone rules are defined by governments and change frequently. There are a number of organizations, known here as groups, that monitor time-zone changes and collate them. The default group is the IANA Time Zone Database (TZDB). Other organizations include IATA (the airline industry body) and Microsoft.
Each group defines its own format for the region ID it provides. The TZDB group defines IDs such as 'Europe/London' or 'America/New_York'. TZDB IDs take precedence over other groups.
It is strongly recommended that the group name is included in all IDs supplied by groups other than TZDB to avoid conflicts. For example, IATA airline time-zone region IDs are typically the same as the three letter airport code. However, the airport of Utrecht has the code 'UTC', which is obviously a conflict. The recommended format for region IDs from groups other than TZDB is 'group~region'. Thus if IATA data were defined, Utrecht airport would be 'IATA~UTC'.
Serialization
This class can be serialized and stores the string zone ID in the external form. TheZoneOffset
subclass uses a dedicated format that only stores the
offset from UTC/Greenwich.
A ZoneId
can be deserialized in a Java Runtime where the ID is unknown.
For example, if a server-side Java Runtime has been updated with a new zone ID, but
the client-side Java Runtime has not been updated. In this case, the ZoneId
object will exist, and can be queried using getId
, equals
,
hashCode
, toString
, getDisplayName
and normalized
.
However, any call to getRules
will fail with ZoneRulesException
.
This approach is designed to allow a ZonedDateTime
to be loaded and
queried, but not modified, on a Java Runtime with incomplete time-zone information.
This is a value-based
class; programmers should treat instances that are
equal as interchangeable and should not
use instances for synchronization, or unpredictable behavior may
occur. For example, in a future release, synchronization may fail.
The equals
method should be used for comparisons.
- Implementation Requirements:
- This abstract sealed class permits two implementations, both of which are immutable and
thread-safe. One implementation models region-based IDs, the other is
ZoneOffset
modelling offset-based IDs. This difference is visible in serialization. - Sealed Class Hierarchy Graph:
- Since:
- 1.8
- See Also:
-
Field Summary
-
Method Summary
Modifier and TypeMethodDescriptionboolean
Checks if this time-zone ID is equal to another time-zone ID.static ZoneId
from
(TemporalAccessor temporal) Obtains an instance ofZoneId
from a temporal object.Gets the set of available zone IDs.getDisplayName
(TextStyle style, Locale locale) Gets the textual representation of the zone, such as 'British Time' or '+02:00'.abstract String
getId()
Gets the unique time-zone ID.abstract ZoneRules
getRules()
Gets the time-zone rules for this ID allowing calculations to be performed.int
hashCode()
A hash code for this time-zone ID.Normalizes the time-zone ID, returning aZoneOffset
where possible.static ZoneId
Obtains an instance ofZoneId
from an ID ensuring that the ID is valid and available for use.static ZoneId
Obtains an instance ofZoneId
using its ID using a map of aliases to supplement the standard zone IDs.static ZoneId
ofOffset
(String prefix, ZoneOffset offset) Obtains an instance ofZoneId
wrapping an offset.static ZoneId
Gets the system default time-zone.toString()
Outputs this zone as aString
, using the ID.
-
Field Details
-
SHORT_IDS
A map of zone overrides to enable the short time-zone names to be used.Use of short zone IDs has been deprecated in
java.util.TimeZone
. This map allows the IDs to continue to be used via theof(String, Map)
factory method.This map contains a mapping of the IDs that is in line with TZDB 2024b and later, where 'EST', 'MST' and 'HST' map to IDs which do not include daylight savings since 1970. This mapping may change in update releases in support of new versions of TZDB.
This maps as follows:
- ACT - Australia/Darwin
- AET - Australia/Sydney
- AGT - America/Argentina/Buenos_Aires
- ART - Africa/Cairo
- AST - America/Anchorage
- BET - America/Sao_Paulo
- BST - Asia/Dhaka
- CAT - Africa/Harare
- CNT - America/St_Johns
- CST - America/Chicago
- CTT - Asia/Shanghai
- EAT - Africa/Addis_Ababa
- ECT - Europe/Paris
- EST - America/Panama
- HST - Pacific/Honolulu
- IET - America/Indiana/Indianapolis
- IST - Asia/Kolkata
- JST - Asia/Tokyo
- MIT - Pacific/Apia
- MST - America/Phoenix
- NET - Asia/Yerevan
- NST - Pacific/Auckland
- PLT - Asia/Karachi
- PNT - America/Phoenix
- PRT - America/Puerto_Rico
- PST - America/Los_Angeles
- SST - Pacific/Guadalcanal
- VST - Asia/Ho_Chi_Minh
-
-
Method Details
-
systemDefault
Gets the system default time-zone.This queries
TimeZone.getDefault()
to find the default time-zone and converts it to aZoneId
. If the system default time-zone is changed, then the result of this method will also change.- Returns:
- the zone ID, not null
- Throws:
DateTimeException
- if the converted zone ID has an invalid formatZoneRulesException
- if the converted zone region ID cannot be found
-
getAvailableZoneIds
Gets the set of available zone IDs.This set includes the string form of all available region-based IDs. Offset-based zone IDs are not included in the returned set. The ID can be passed to
of(String)
to create aZoneId
.The set of zone IDs can increase over time, although in a typical application the set of IDs is fixed. Each call to this method is thread-safe.
- Returns:
- a modifiable copy of the set of zone IDs, not null
-
of
Obtains an instance ofZoneId
using its ID using a map of aliases to supplement the standard zone IDs.Many users of time-zones use short abbreviations, such as PST for 'Pacific Standard Time' and PDT for 'Pacific Daylight Time'. These abbreviations are not unique, and so cannot be used as IDs. This method allows a map of string to time-zone to be setup and reused within an application.
- Parameters:
zoneId
- the time-zone ID, not nullaliasMap
- a map of alias zone IDs (typically abbreviations) to real zone IDs, not null- Returns:
- the zone ID, not null
- Throws:
DateTimeException
- if the zone ID has an invalid formatZoneRulesException
- if the zone ID is a region ID that cannot be found
-
of
Obtains an instance ofZoneId
from an ID ensuring that the ID is valid and available for use.This method parses the ID producing a
ZoneId
orZoneOffset
. AZoneOffset
is returned if the ID is 'Z', or starts with '+' or '-'. The result will always be a valid ID for whichZoneRules
can be obtained.Parsing matches the zone ID step by step as follows.
- If the zone ID equals 'Z', the result is
ZoneOffset.UTC
. - If the zone ID consists of a single letter, the zone ID is invalid
and
DateTimeException
is thrown. - If the zone ID starts with '+' or '-', the ID is parsed as a
ZoneOffset
usingZoneOffset.of(String)
. - If the zone ID equals 'GMT', 'UTC' or 'UT' then the result is a
ZoneId
with the same ID and rules equivalent toZoneOffset.UTC
. - If the zone ID starts with 'UTC+', 'UTC-', 'GMT+', 'GMT-', 'UT+' or 'UT-'
then the ID is a prefixed offset-based ID. The ID is split in two, with
a two or three letter prefix and a suffix starting with the sign.
The suffix is parsed as a
ZoneOffset
. The result will be aZoneId
with the specified UTC/GMT/UT prefix and the normalized offset ID as perZoneOffset.getId()
. The rules of the returnedZoneId
will be equivalent to the parsedZoneOffset
. - All other IDs are parsed as region-based zone IDs. Region IDs must
match the regular expression
[A-Za-z][A-Za-z0-9~/._+-]+
otherwise aDateTimeException
is thrown. If the zone ID is not in the configured set of IDs,ZoneRulesException
is thrown. The detailed format of the region ID depends on the group supplying the data. The default set of data is supplied by the IANA Time Zone Database (TZDB). This has region IDs of the form '{area}/{city}', such as 'Europe/Paris' or 'America/New_York'. This is compatible with most IDs fromTimeZone
.
- Parameters:
zoneId
- the time-zone ID, not null- Returns:
- the zone ID, not null
- Throws:
DateTimeException
- if the zone ID has an invalid formatZoneRulesException
- if the zone ID is a region ID that cannot be found
- If the zone ID equals 'Z', the result is
-
ofOffset
Obtains an instance ofZoneId
wrapping an offset.If the prefix is "GMT", "UTC", or "UT" a
ZoneId
with the prefix and the non-zero offset is returned. If the prefix is empty""
theZoneOffset
is returned.- Parameters:
prefix
- the time-zone ID, not nulloffset
- the offset, not null- Returns:
- the zone ID, not null
- Throws:
IllegalArgumentException
- if the prefix is not one of "GMT", "UTC", or "UT", or ""
-
from
Obtains an instance ofZoneId
from a temporal object.This obtains a zone based on the specified temporal. A
TemporalAccessor
represents an arbitrary set of date and time information, which this factory converts to an instance ofZoneId
.A
TemporalAccessor
represents some form of date and time information. This factory converts the arbitrary temporal object to an instance ofZoneId
.The conversion will try to obtain the zone in a way that favours region-based zones over offset-based zones using
TemporalQueries.zone()
.This method matches the signature of the functional interface
TemporalQuery
allowing it to be used as a query via method reference,ZoneId::from
.- Parameters:
temporal
- the temporal object to convert, not null- Returns:
- the zone ID, not null
- Throws:
DateTimeException
- if unable to convert to aZoneId
-
getId
Gets the unique time-zone ID.This ID uniquely defines this object. The format of an offset based ID is defined by
ZoneOffset.getId()
.- Returns:
- the time-zone unique ID, not null
-
getDisplayName
Gets the textual representation of the zone, such as 'British Time' or '+02:00'.This returns the textual name used to identify the time-zone ID, suitable for presentation to the user. The parameters control the style of the returned text and the locale.
If no textual mapping is found then the
full ID
is returned.- Parameters:
style
- the length of the text required, not nulllocale
- the locale to use, not null- Returns:
- the text value of the zone, not null
-
getRules
Gets the time-zone rules for this ID allowing calculations to be performed.The rules provide the functionality associated with a time-zone, such as finding the offset for a given instant or local date-time.
A time-zone can be invalid if it is deserialized in a Java Runtime which does not have the same rules loaded as the Java Runtime that stored it. In this case, calling this method will throw a
ZoneRulesException
.The rules are supplied by
ZoneRulesProvider
. An advanced provider may support dynamic updates to the rules without restarting the Java Runtime. If so, then the result of this method may change over time. Each individual call will be still remain thread-safe.ZoneOffset
will always return a set of rules where the offset never changes.- Returns:
- the rules, not null
- Throws:
ZoneRulesException
- if no rules are available for this ID
-
normalized
Normalizes the time-zone ID, returning aZoneOffset
where possible.The returns a normalized
ZoneId
that can be used in place of this ID. The result will haveZoneRules
equivalent to those returned by this object, however the ID returned bygetId()
may be different.The normalization checks if the rules of this
ZoneId
have a fixed offset. If they do, then theZoneOffset
equal to that offset is returned. Otherwisethis
is returned.- Returns:
- the time-zone unique ID, not null
-
equals
-
hashCode
-
toString
-