如何在特定时区（“欧洲/巴黎”）中获取今天的 startDate 和 endDate 的 UTC 瞬间

Question

I want to get the UTC instant (since my DB is storing in UTC) from Java (which is also in UTC) of a particular time zone, this is what I have tried so far:

    public static Instant getStartOfTheDayDateTime(Instant instant, String zoneId) {

        ZonedDateTime zoned = instant.atZone(ZONE_ID_TO_ZONE_MAP.get(zoneId));
        ZoneId zone = ZoneId.of(zoneId);

        return zoned.toLocalDate().atStartOfDay(zone).toInstant();
//        ZonedDateTime startOfTheDay = zoned.withHour(0)
//                .withMinute(0)
//                .withSecond(0)
//                .withNano(0);
//
//        return startOfTheDay.toInstant();
    }

    public static Instant getEndOfTheDayDateTime(Instant instant, String zoneId) {
        ZonedDateTime zoned = instant.atZone(ZONE_ID_TO_ZONE_MAP.get(zoneId));
        ZonedDateTime endOfTheDay = zoned.withHour(0)
                .withMinute(0)
                .withSecond(0)
                .withNano(0)
                .plusDays(1);
        return endOfTheDay.toInstant();

    }

Every attempt shows:

2020-04-10 22:00:00.0(Timestamp), 2020-04-11 22:00:00.0(Timestamp)

• Is this the start/end of the day UTC time in Europe/Paris zone?
• I was expecting to have 2020-04-11 02:00:00.0(Timestamp), 2020-04-12 02:00:00.0(Timestamp)

Answer 1

Right now, Paris is on summer time: UTC+2. Paris is 'ahead' of UTC by 2 hours.

So 00:00:00 in Paris local time is 22:00:00 UTC.

Answer 2

Is this the start/end of the day UTC time in Europe/Paris zone?

Yes. Europe/Paris is in daylight savings time. Midnight in Paris occurred at 22:00 UTC time.

I was expecting to have 2020-04-11 02:00:00.0(Timestamp), 2020-04-12 02:00:00.0(Timestamp)

That's not right, 02:00 UTC would have been 04:00 in Paris time.

Answer 3

Ask programmatically if a moment is in DST

Is this the start/end of the day UTC time in Europe/Paris zone?

Get start of day.

ZoneId z = ZoneId.of( "Europe/Paris" );
ZonedDateTime zdtStartOfDay = instant.atZone( z ).toLocalDate().atStartOfDay( z ) ; 

Ask if that moment is in DST for that zone.

ZoneRules rules = z.getRules();
boolean isDst = rules.isDaylightSavings( zdtStartOfDay.toInstant() );

Pass date-time objects rather than mere strings

public static Instant getStartOfTheDayDateTime(Instant instant, String zoneId)

I suggest you ask the calling programmer to pass a valid ZoneId object rather than a mere string. It should not be the job of this method to validate their string input. If it is reasonable to expect a Instant then it is also reasonable to expect a ZoneId .

 public static Instant getStartOfTheDayDateTime(Instant instant, ZoneID zoneId )

Half-Open

public static Instant getEndOfTheDayDateTime(Instant instant, String zoneId) {

Trying to determine the last moment of the day is impossible because of infinitely divisible last second.

Also this approach to defining a span of time is awkward. It makes abutting multiple spans tricky. Various software systems and protocols differ in their resolution of that last fractional second, using milliseconds, microseconds, nanoseconds, or some other fraction.

The common practice in date-time handling is to track a span of time using the Half-Open approach. In Half-Open, the beginning is inclusive while the ending is exclusive .

So a full day begins with the first moment of the day and runs up to, but does not include, the first moment of the next day.

ZoneId z = ZoneId.of( "Europe/Paris" );
ZonedDateTime zdtStartOfDay = instant.atZone( z ).toLocalDate().atStartOfDay( z ) ; 
ZonedDateTime zdtStartOfNextDay = instant.atZone( z ).toLocalDate().plusDays( 1 ).atStartOfDay( z ) ;

You might want to break that code out to more lines, for easier reading/debugging.

Instant instant = Instant.now() ;  // Or passed in. 
ZoneId z = ZoneId.of( "Europe/Paris" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;
LocalDate ld = zdt.toLocalDate() ;
LocalDate ldNextDay = ld.plusDays( 1 ) ;
ZonedDateTime zdtStartOfNextDay = ldNextDay.atStartOfDay( z ) ;

See this code run live at IdeOne.com . For example:

System.out.println( instant ) ;             // 2020-04-13T00:15:25.235341Z
System.out.println( zdt ) ;                 // 2020-04-13T02:15:25.235341+02:00[Europe/Paris]
System.out.println( ld ) ;                  // 2020-04-13
System.out.println( ldNextDay ) ;           // 2020-04-14
System.out.println( zdtStartOfNextDay ) ;   // 2020-04-14T00:00+02:00[Europe/Paris]

ThreeTen-Extra Interval

If you do this kind of work with spans of time often, then I suggest adding the ThreeTen-Extra library to your project. That library includes the Interval class to track a span-of-time as aa pair of Instant objects.

Interval interval = Interval.of( zdtStartOfDay.toInstant() , zdtStartOfNextDay.toInstant() ) ;

You can then make use the several handy comparison methods such as abuts , contains , encloses , intersection , overlaps , and union .

Timestamp

Never use the java.sql.Timestamp class. This class is part of the terrible date-time classes that shipped with the earliest versions of Java. These classes are now legacy, supplanted entirely by the modern java.time classes defined in JSR 310 and built into Java 8 and later.

As of JDBC 4.2 we can exchange java.time objects with a database. Use getObject and setObject and updateObject .

The JDBC spec oddly requires support for OffsetDateTime but not the more commonly used Instant and ZonedDateTime . Your particular driver may support these other types. If not, convert.

Retrieval from database.

OffsetDateTime odt = myResultSet.getObject( … , OffsetDateTime.class ) ;
Instant instant = odt.toInstant() ;

Sending to the database.

OffsetDateTime odt = instant.atOffset( ZoneOffset.UTC ) ;
myPreparedStatement.setObject( … , odt ) ;