Get GMT Time in Java

Question

In Java  I want to get the current time in GMT   I tried various options like this   Date date   new Date    Calendar calendar   Calendar getInstance TimeZone getTimeZone  GMT     date1   calendar getTime      But the date is always is interpreted in my local time zone   What am I doing wrong and how can I convert a java Date to GMT

User · Answer

After java 8  you may want to get the formatted time as below    DateTimeFormatter ofPattern  HH mm ss SSS   format LocalTime now ZoneId of  GMT

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The following code will get the date minus timezone offset   protected Date toGmt0 ZonedDateTime time        ZonedDateTime gmt0   time minusSeconds time getOffset   getTotalSeconds         return Date from gmt0 toInstant         Test public void test          ZonedDateTime now   ZonedDateTime now        Date dateAtSystemZone   Date from now toInstant         Date dateAtGmt0   toGmt0 now        SimpleDateFormat sdfWithoutZone   new SimpleDateFormat  yyyy-MM-dd HH mm ss SSS        SimpleDateFormat sdfWithZoneGmt0   new SimpleDateFormat  yyyy-MM-dd HH mm ss SSS   Locale ITALIAN       sdfWithZoneGmt0 setTimeZone TimeZone getTimeZone  GMT          System out println                    ndateAtSystemZone                dateAtSystemZone                 ndateAtGmt0                      dateAtGmt0                 ndiffInMillis                     dateAtSystemZone getTime   - dateAtGmt0 getTime                    n                  ndateWithSystemZone format       sdfWithoutZone format dateAtSystemZone                  ndateAtGmt0 format               sdfWithoutZone format dateAtGmt0                  n                  ndateFormatWithGmt0              sdfWithZoneGmt0 format dateAtSystemZone           output    dateAtSystemZone            Thu Apr 23 14 03 36 CST 2020 dateAtGmt0                  Thu Apr 23 06 03 36 CST 2020 diffInMillis                28800000  dateWithSystemZone format   2020-04-23 14 03 36 140 dateAtGmt0 format           2020-04-23 06 03 36 140  dateFormatWithGmt0          2020-04-23 06 03 36 140   My system is at GMT 8  so diffInMillis   28800000   8   60   60   1000

User · Answer

To get the time in millis at GMT all you need is  long millis   System currentTimeMillis      You can also do  long millis   new Date   getTime      and  long millis        Calendar getInstance TimeZone getTimeZone  GMT    getTimeInMillis      but these are inefficient ways of making the same call

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Odds are good you did the right stuff on the back end in getting the date  but there s nothing to indicate that you didn t take that GMT time and format it according to your machine s current locale   final Date currentTime   new Date     final SimpleDateFormat sdf           new SimpleDateFormat  EEE  MMM d  yyyy hh mm ss a z        Give it to me in GMT time  sdf setTimeZone TimeZone getTimeZone  GMT     System out println  GMT time      sdf format currentTime      The key is to use your own DateFormat  not the system provided one   That way you can set the DateFormat s timezone to what you wish  instead of it being set to the Locale s timezone

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This is pretty simple and straight forward   Date date   new Date    TimeZone setDefault TimeZone getTimeZone  GMT     Calendar cal   Calendar getInstance TimeZone getDefault     date   cal getTime      Now date will contain the current GMT time

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Useful Utils methods as below for manage Time in GMT with DST Savings   public static Date convertToGmt Date date        TimeZone tz   TimeZone getDefault        Date ret   new Date date getTime   - tz getRawOffset             if we are now in DST  back off by the delta   Note that we are checking the GMT date  this is the KEY      if  tz inDaylightTime ret             Date dstDate   new Date ret getTime   - tz getDSTSavings                 check to make sure we have not crossed back into standard time            this happens when we are on the cusp of DST  7pm the day before the change for PDT          if  tz inDaylightTime dstDate                 ret   dstDate                      return ret     public static Date convertFromGmt Date date        TimeZone tz   TimeZone getDefault        Date ret   new Date date getTime     tz getRawOffset             if we are now in DST  back off by the delta   Note that we are checking the GMT date  this is the KEY      if  tz inDaylightTime ret             Date dstDate   new Date ret getTime     tz getDSTSavings                 check to make sure we have not crossed back into standard time            this happens when we are on the cusp of DST  7pm the day before the change for PDT          if  tz inDaylightTime dstDate                 ret   dstDate                      return ret

User · Answer

From my experience  the bundled Calendar and Date classes in Java can yield undersired effect  If you wouldn t mind upgrading to Java 8  then consider using ZonedDateTime  like so   ZonedDateTime currentDate   ZonedDateTime now  ZoneOffset UTC

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After trying a lot of methods  I found out  to get the time in millis at GMT you need to create two separate SimpleDateFormat objects  one for formatting in GMT and another one for parsing    Here is the code    SimpleDateFormat format   new SimpleDateFormat  yyyy-MM-dd HH mm ss     format setTimeZone TimeZone getTimeZone  UTC      Date date   new Date     SimpleDateFormat dateParser   new SimpleDateFormat  yyyy-MM-dd HH mm ss     Date dateTime  dateParser parse format format date     long gmtMilliSeconds   dateTime getTime      This works fine

User · Answer

You can   t  First  you are asking the impossible  An old-fashioned Date object hasn   t got  as in cannot have a time zone or GMT offset      But the date is always is interpreted in my local time zone    I suppose that you have printed the Date or done something else that implicitly calls it toString method  I believe that this is the only time that the Date is interpreted in your time zone  More precisely in the current default time zone of your JVM  On the other hand this is unavoidable  Date toString   does behave in that way  it picks up the JVM   s time zone setting and uses it for rendering the string to be returned   You can with java time  You shouldn   t use a Date  though  That class is poorly designed and fortunately long outdated  Also java time  the modern Java date and time API that replaces it  has a class or two for dates and times with offset from GMT or UTC  I am considering GMT and UTC synonymous for now  strictly speaking they are not       OffsetDateTime now   OffsetDateTime now ZoneOffset UTC       System out println  Time now in UTC  GMT  is     now     When I ran this snippet just now  the output was      Time now in UTC  GMT  is 2019-06-17T11 51 38 246188Z   The trailing Z of the output means UTC   Links   Oracle tutorial  Date Time explaining how to use java time  The Difference Between GMT and UTC on timeanddate com

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I wonder why no one does this   Calendar time   Calendar getInstance    time add Calendar MILLISECOND  -time getTimeZone   getOffset time getTimeInMillis      Date date   time getTime        Update  Since Java 8 9 10 and more  there should be better alternatives supported by Java  Thanks for your comment  humanity

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tl dr  Instant now     java time  The Answer by Damilola is correct in suggesting you use the java time framework built into Java 8 and later  But that Answer uses the ZonedDateTime class which is overkill if you just want UTC rather than any particular time zone    The troublesome old date-time classes are now legacy  supplanted by the java time classes   Instant  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     Simple code    Instant instant   Instant now          instant toString    2016-11-29T23 18 14 604Z   You can think of Instant as the building block to which you can add a time zone  ZoneID  to get a ZonedDateTime    ZoneId z   ZoneId of   America Montreal     ZonedDateTime zdt   instant atZone  z        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   amp  SimpleDateFormat   The Joda-Time project  now in maintenance mode  advises migration to java time   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  amp  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] Get GMT Time in Java

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