tl;dr
ZoneId z = ZoneId.of( "America/Montreal" ); // A date only has meaning within a specific time zone. At any given moment, the date varies around the globe by zone.
LocalDate ld =
givenJavaUtilDate.toInstant() // Convert from legacy class `Date` to modern class `Instant` using new methods added to old classes.
.atZone( z ) // Adjust into the time zone in order to determine date.
.toLocalDate(); // Extract date-only value.
LocalDate today = LocalDate.now( z ); // Get today’s date for specific time zone.
LocalDate kwanzaaStart = today.withMonth( Month.DECEMBER ).withDayOfMonth( 26 ); // Kwanzaa starts on Boxing Day, day after Christmas.
LocalDate kwanzaaStop = kwanzaaStart.plusWeeks( 1 ); // Kwanzaa lasts one week.
Boolean isDateInKwanzaaThisYear = (
( ! today.isBefore( kwanzaaStart ) ) // Short way to say "is equal to or is after".
&&
today.isBefore( kwanzaaStop ) // Half-Open span of time, beginning inclusive, ending is *exclusive*.
)
Half-Open
Date-time work commonly employs the "Half-Open" approach to defining a span of time. The beginning is inclusive while the ending is exclusive. So a week starting on a Monday runs up to, but does not include, the following Monday.
java.time
Java 8 and later comes with the java.time
framework built-in. Supplants the old troublesome classes including java.util.Date/.Calendar
and SimpleDateFormat
. Inspired by the successful Joda-Time library. Defined by JSR 310. Extended by the ThreeTen-Extra project.
An Instant
is a moment on the timeline in UTC with nanosecond resolution.
Instant
Convert your java.util.Date
objects to Instant objects.
Instant start = myJUDateStart.toInstant();
Instant stop = …
If getting java.sql.Timestamp
objects through JDBC from a database, convert to java.time.Instant in a similar way. A java.sql.Timestamp
is already in UTC so no need to worry about time zones.
Instant start = mySqlTimestamp.toInstant() ;
Instant stop = …
Get the current moment for comparison.
Instant now = Instant.now();
Compare using the methods isBefore, isAfter, and equals.
Boolean containsNow = ( ! now.isBefore( start ) ) && ( now.isBefore( stop ) ) ;
LocalDate
Perhaps you want to work with only the date, not the time-of-day.
The LocalDate
class represents a date-only value, without time-of-day and without time zone.
LocalDate start = LocalDate.of( 2016 , 1 , 1 ) ;
LocalDate stop = LocalDate.of( 2016 , 1 , 23 ) ;
To get the current date, specify a time zone. At any given moment, today’s date varies by time zone. For example, a new day dawns earlier in Paris than in Montréal.
LocalDate today = LocalDate.now( ZoneId.of( "America/Montreal" ) );
We can use the isEqual
, isBefore
, and isAfter
methods to compare. In date-time work we commonly use the Half-Open approach where the beginning of a span of time is inclusive while the ending is exclusive.
Boolean containsToday = ( ! today.isBefore( start ) ) && ( today.isBefore( stop ) ) ;
Interval
If you chose to add the ThreeTen-Extra library to your project, you could use the Interval
class to define a span of time. That class offers methods to test if the interval contains, abuts, encloses, or overlaps other date-times/intervals.
The Interval
class works on Instant
objects. The Instant
class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).
We can adjust the LocalDate
into a specific moment, the first moment of the day, by specifying a time zone to get a ZonedDateTime
. From there we can get back to UTC by extracting a Instant
.
ZoneId z = ZoneId.of( "America/Montreal" );
Interval interval =
Interval.of(
start.atStartOfDay( z ).toInstant() ,
stop.atStartOfDay( z ).toInstant() );
Instant now = Instant.now();
Boolean containsNow = interval.contains( now );
About java.time
The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date
, Calendar
, & SimpleDateFormat
.
The Joda-Time project, now in maintenance mode, advises migration to the java.time
classes.
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
Where to obtain the java.time
classes?
- Java SE 8 and SE 9 and later
- Built-in.
- Part of the standard Java API with a bundled implementation.
- Java 9 adds some minor features and fixes.
- Java SE 6 and SE 7
- Much of the
java.time
functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
- Android
- The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
- See How to use….
The ThreeTen-Extra project extends java.time
with additional classes. This project is a proving ground for possible future additions to java.time
. You may find some useful classes here such as Interval
, YearWeek
, YearQuarter
, and more.
java.util.Date
andjava.util.Calendar
are now legacy, supplanted by the java.time classes. See Tutorial by Oracle. – Jarred