Examples of java.time.ZoneId

java.time.ZoneId
A time-zone ID, such as {@code Europe/Paris}.
A {@code ZoneId} is used to identify the rules used to convert betweenan {@link Instant} and a {@link 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
Most fixed offsets are represented by {@link ZoneOffset}. Calling {@link #normalized()} on any {@code ZoneId} will ensure that afixed offset ID will be represented as a {@code ZoneOffset}.
The actual rules, describing when and how the offset changes, are defined by {@link 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 {@code ZoneId} will only sendthe 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 {@code 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 {@code ZoneOffset} using {@code 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 {@link ZoneRulesProvider}. The configuration focuses on providing the lookup from the ID to the underlying {@code 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. The {@code ZoneOffset} subclass uses a dedicated format that only stores theoffset from UTC/Greenwich.
A {@code 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 {@code ZoneId}object will exist, and can be queried using {@code getId}, {@code equals}, {@code hashCode}, {@code toString}, {@code getDisplayName} and {@code normalized}. However, any call to {@code getRules} will fail with {@code ZoneRulesException}. This approach is designed to allow a {@link ZonedDateTime} to be loaded andqueried, but not modified, on a Java Runtime with incomplete time-zone information.
This is a value-based class; use of identity-sensitive operations (including reference equality ( {@code ==}), identity hash code, or synchronization) on instances of {@code ZoneId} may have unpredictable results and should be avoided.The {@code equals} method should be used for comparisons. @implSpec This abstract class has two implementations, both of which are immutable and thread-safe. One implementation models region-based IDs, the other is {@code ZoneOffset} modellingoffset-based IDs. This difference is visible in serialization. @since 1.8

  public void testIsValid() {
    assertTrue( constraint.isValid( null, null ), "null fails validation." );


    // Test allowed zone offsets (UTC-18 to UTC+18) with 1 hour increments
    for ( int i = -18; i <= 18; i++ ) {
      ZoneId zone = ZoneId.ofOffset( "UTC", ZoneOffset.ofHours( i ) );
      ChronoZonedDateTime future = ZonedDateTime.now( zone ).plusHours( 1 );
      ChronoZonedDateTime past = ZonedDateTime.now( zone ).minusHours( 1 );
      assertTrue( constraint.isValid( past, null ), "Past ZonedDateTime '" + past + "' fails validation.");
      assertFalse( constraint.isValid( future, null ), "Future ZonedDateTime '" + future + "' validated as past.");
    }

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  public void testIsValid() {
    assertTrue( constraint.isValid( null, null ), "null fails validation." );


    // Test allowed zone offsets (UTC-18 to UTC+18) with 1 hour increments
    for ( int i = -18; i <= 18; i++ ) {
      ZoneId zone = ZoneId.ofOffset( "UTC", ZoneOffset.ofHours( i ) );
      ChronoZonedDateTime future = ZonedDateTime.now( zone ).plusHours( 1 );
      ChronoZonedDateTime past = ZonedDateTime.now( zone ).minusHours( 1 );
      assertTrue( constraint.isValid( future, null ), "Future ZonedDateTime '" + future + "' fails validation." );
      assertFalse( constraint.isValid( past, null ), "Past ZonedDateTime '" + past + "' validated as future." );
    }

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        Instant instant = clock.instant();
        Date legacyDate = Date.from(instant);




        ZoneId zone1 = ZoneId.of("Europe/Berlin");
        ZoneId zone2 = ZoneId.of("Brazil/East");


        System.out.println(zone1.getRules());
        System.out.println(zone2.getRules());


        // time
        LocalTime now1 = LocalTime.now(zone1);
        LocalTime now2 = LocalTime.now(zone2);

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   */
  @Test
  public void testZoneIdRegionAndFixedOffset() {
    // Create zoned date/time using ZoneId to parse an IANA area/region format TZ ID (use one that doesn't vary with
    // daylight saving to ensure this test-case is stable)
    final ZoneId zoneId = ZoneId.of("Africa/Addis_Ababa");
    final ZonedDateTime zonedDateTime = ZonedDateTime.of(2014, Month.AUGUST.getValue(), 30, 21, 40, 20, 0, zoneId);


    // Use ZoneOffset to return the fixed offset of a zoned date/time from UTC
    final ZoneOffset zoneOffset = zonedDateTime.getOffset();
    int threeHoursInSeconds = 3 * 60 * 60;

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Examples of java.time.ZoneId

Time-zone IDs

Serialization

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