How can I tell if a Java Date and time zone is before the current time?

Question

My class has 2 properties that make up its date:

java.util.Date date;
String timeZone;

How can I see if this date is before the current time on the server?

Basically I want to write something like this, but take timeZone into account:

return date.before(new Date());

Answer 1

Date stores internally as UTC, so your timeZone variable is not necessary. You can simply use Date.before(Date) .

Answer 2

    Calendar startCalendar = Calendar.getInstance();
    int startTimeZoneOffset = TimeZone.getTimeZone(timeZone).getOffset(startDate.getTime()) / 1000 / 60;
    startCalendar.setTime(startDate);
    startCalendar.add(Calendar.MINUTE, startTimeZoneOffset);

    Calendar nowCalendar = Calendar.getInstance();
    int nowTimeZoneOffset = nowCalendar.getTimeZone().getOffset(new Date().getTime()) / 1000 / 60;
    nowCalendar.setTime(new Date());
    nowCalendar.add(Calendar.MINUTE, nowTimeZoneOffset);

    return startCalendar.before(nowCalendar);

Answer 3

tl;dr

Use Instant class, which is always in UTC . So time zone becomes a non-issue.

someInstant.isBefore( Instant.now() )

java.time

The modern approach uses the java.time classes that supplanted the terrible Date & Calendar classes.

As the correct Answer by Kuo stated, your java.util.Date is recording a moment in UTC. So no need for a time zone.

Likewise, its replacement, the java.time.Instant class, also records a moment in UTC. So no time zone needed.

Instant instant = Instant.now() ;  // Capture current in UTC. 

So all you need as member variables on your class is Instant .

public class Event {
    Instant when ;
    …
}

To compare Instant objects, use the isAfter , isBefore , and equals methods.

someInstant.isBefore( Instant.now() ) 

For presentation in a time zone expected by the user, assign a ZoneId to get a ZonedDateTime object. The Instant and the ZonedDateTime both represent the same moment, the same point on the timeline, but viewed through different wall-clock time.

ZoneId z = ZoneId.of( "America/Montreal" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;     // Same moment, different wall-clock time.
String output = zdt.toString() ;              // Generate text in standard ISO 8601 format, wisely extended to append the name of the zone in square brackets.

Or let java.time automatically localize output. To localize, specify:

• FormatStyle to determine how long or abbreviated should the string be.
• Locale to determine:
  • The human language for translation of name of day, name of month, and such.
  • The cultural norms deciding issues of abbreviation, capitalization, punctuation, separators, and such.

Example:

Locale l = Locale.CANADA_FRENCH ;   // Or Locale.US, Locale.JAPAN, etc.
DateTimeFormatter f = DateTimeFormatter.ofLocalizedDateTime( FormatStyle.FULL )
                                       .withLocale( l );
String output = zdt.format( f );

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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 .

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , Java SE 10 , Java SE 11 , and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP… .

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 .