How to tackle daylight savings using TimeZone in Java

Question

I have to print the EST time in my Java application  I had set the time zone to EST using   Calendar cal   Calendar getInstance TimeZone getTimeZone  EST       But when the daylight savings is being followed in this timezone  my code does not print the correct time  it prints 1 hour less    How to make the code work to read the correct time always  irrespective of whether the daylight savings are being observed or not   PS  I tried setting the timezone to EDT  but it doesn t solve the problem

User · Answer

Other answers are correct  especially the one by Jon Skeet  but outdated    java time  These old date-time classes have been supplanted by the java time framework built into Java 8 and later   If you simply want the current time in UTC  use the Instant class   Instant now   Instant now      EST is not a time zone  as explained in the correct Answer by Jon Skeet  Such 3-4 letter codes are neither standardized nor unique  and further the confusion over Daylight Saving Time  DST   Use a proper time zone name in the  continent region  format   Perhaps you meant Eastern Standard Time in east coast of north America  Or Egypt Standard Time  Or European Standard Time   ZoneId zoneId   ZoneId of   America New York     ZoneId zoneId   ZoneId of   Africa Cairo     ZoneId zoneId   ZoneId of   Europe Lisbon       Use any such ZoneId object to get the current moment adjusted to a particular time zone to produce a ZonedDateTime object   ZonedDateTime zdt   ZonedDateTime now  zoneId       Adjust that ZonedDateTime into a different time zone by producing another ZonedDateTime object from the first  The java time framework uses immutable objects rather than changing  mutating  existing objects   ZonedDateTime zdtGuam   zdt withZoneSameInstant  ZoneId of   Pacific Guam

User · Answer

This is the problem to start with   Calendar cal   Calendar getInstance TimeZone getTimeZone  EST       The 3-letter abbreviations should be wholeheartedly avoided in favour of TZDB zone IDs  EST is Eastern Standard Time - and Standard time never observes DST  it s not really a full time zone name  It s the name used for part of a time zone   Unfortunately I haven t come across a good term for this  half time zone  concept    You want a full time zone name  For example  America New York is in the Eastern time zone   TimeZone zone   TimeZone getTimeZone  America New York    DateFormat format   DateFormat getDateTimeInstance    format setTimeZone zone    System out println format format new Date

User · Answer

Implementing the TimeZone class to set the timezone to the Calendar takes care of the daylight savings   java util TimeZone represents a time zone offset  and also figures out daylight savings   sample code   TimeZone est timeZone   TimeZoneIDProvider getTimeZoneID TimeZoneID US EASTERN  getTimeZone    Calendar enteredCalendar   Calendar getInstance    enteredCalendar setTimeZone est timeZone

User · Answer

public static float calculateTimeZone String deviceTimeZone        float ONE HOUR MILLIS   60   60   1000          Current timezone and date     TimeZone timeZone   TimeZone getTimeZone deviceTimeZone       Date nowDate   new Date        float offsetFromUtc   timeZone getOffset nowDate getTime      ONE HOUR MILLIS          Daylight Saving time     if  timeZone useDaylightTime                 DST is used            I m saving this is preferences for later use             save the offset value to use it later         float dstOffset   timeZone getDSTSavings     ONE HOUR MILLIS             DstOffsetValue   dstOffset            I m saving this is preferences for later use            save that now we are in DST mode         if  timeZone inDaylightTime nowDate                 Log e Utility class getName     in Daylight Time                return - ONE HOUR MILLIS   dstOffset             else               Log e Utility class getName     not in Daylight Time                return 0                  else         return 0

User · Answer

Instead of entering  EST  for the timezone you can enter  EST5EDT  as such  As you noted  just  EDT  does not work  This will account for the daylight savings time issue  The code line looks like this   Calendar cal   Calendar getInstance TimeZone getTimeZone  EST5EDT

User · Answer

In java  DateFormatter by default uses DST To avoid day Light saving  DST  you need to manually do a trick  first you have to get the DST offset i e  for how many millisecond DST applied  for ex somewhere DST is also for 45 minutes and for some places it is for 30 min but in most cases DST is of 1 hour you have to use Timezone object and check with the date whether it is falling under DST or not and then you have to manually add offset of DST into it  for eg    TimeZone tz   TimeZone getTimeZone  EST     boolean isDST   tz inDaylightTime yourDateObj    if isDST    int sec  tz getDSTSavings   1000    for no  of seconds  Calendar cal  Calendar getInstance     cal setTime yourDateObj    cal add Calendar Seconds sec    System out println cal getTime       your Date with DST neglected

User · Answer

private static Long DateTimeNowTicks        long TICKS AT EPOCH   621355968000000000L      TimeZone timeZone   Calendar getInstance   getTimeZone        int offs   timeZone getRawOffset        if  timeZone inDaylightTime new Date             offs    60   60   1000      return  System currentTimeMillis     offs    10000   TICKS AT EPOCH

User · Answer

As per this answer   TimeZone tz   TimeZone getTimeZone  EST    boolean inDs   tz inDaylightTime new Date

[java] How to tackle daylight savings using TimeZone in Java

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