SimpleDateFormat parse loses timezone

Question

Code    SimpleDateFormat sdf   new SimpleDateFormat  yyyy MM dd HH mm ss z        sdf setTimeZone TimeZone getTimeZone  GMT         System out println new Date         try           String d   sdf format new Date             System out println d           System out println sdf parse d          catch  Exception e            e printStackTrace       To change body of catch statement use File   Settings   File Templates          Output    Thu Aug 08 17 26 32 GMT 08 00 2013 2013 08 08 09 26 32 GMT Thu Aug 08 17 26 32 GMT 08 00 2013   Note that format   formats the Date correctly to GMT  but parse   lost the GMT details  I know I can use substring   and work around this  but what is the reason underlying this phenomenon   Here is a duplicate question which doesn t have any answers   Edit  Let me put the question in another way  what is the way to retrieve a Date object so that its always in GMT

User · Accepted Answer

All I needed was this     SimpleDateFormat sdf   new SimpleDateFormat  yyyy MM dd HH mm ss    sdf setTimeZone TimeZone getTimeZone  GMT      SimpleDateFormat sdfLocal   new SimpleDateFormat  yyyy MM dd HH mm ss     try       String d   sdf format new Date         System out println d       System out println sdfLocal parse d      catch  Exception e        e printStackTrace       To change body of catch statement use File   Settings   File Templates      Output   slightly dubious  but I want only the date to be consistent  2013 08 08 11 01 08 Thu Aug 08 11 01 08 GMT 08 00 2013

User · Answer

OP s solution to his problem  as he says  has dubious output  That code still shows confusion about representations of time  To clear up this confusion  and make code that won t lead to wrong times  consider this extension of what he did   public static void  testDateFormatting         SimpleDateFormat sdfGMT1   new SimpleDateFormat  yyyy MM dd HH mm ss        sdfGMT1 setTimeZone TimeZone getTimeZone  GMT         SimpleDateFormat sdfGMT2   new SimpleDateFormat  yyyy MM dd HH mm ss z        sdfGMT2 setTimeZone TimeZone getTimeZone  GMT          SimpleDateFormat sdfLocal1   new SimpleDateFormat  yyyy MM dd HH mm ss        SimpleDateFormat sdfLocal2   new SimpleDateFormat  yyyy MM dd HH mm ss z         try           Date d   new Date            String s1   d toString            String s2   sdfLocal1 format d              Store s3 or s4 in database          String s3   sdfGMT1 format d           String s4   sdfGMT2 format d              Retrieve s3 or s4 from database  using LOCAL sdf          String s5   sdfLocal1 parse s3  toString              EXCEPTION String s6   sdfLocal2 parse s3  toString            String s7   sdfLocal1 parse s4  toString            String s8   sdfLocal2 parse s4  toString               Retrieve s3 from database  using GMT sdf             Note that this is the SAME sdf that created s3          Date d2   sdfGMT1 parse s3           String s9   d2 toString            String s10   sdfGMT1 format d2           String s11   sdfLocal2 format d2         catch  Exception e            e printStackTrace                     examining values in a debugger   s1   Mon Sep 07 06 11 53 EDT 2015   id 831698113128      s2   2015 09 07 06 11 53   id 831698114048   s3   2015 09 07 10 11 53   id 831698114968   s4   2015 09 07 10 11 53 GMT 00 00   id 831698116112     s5   Mon Sep 07 10 11 53 EDT 2015   id 831698116944      s6  -- omitted  gave parse exception     s7   Mon Sep 07 10 11 53 EDT 2015   id 831698118680      s8   Mon Sep 07 06 11 53 EDT 2015   id 831698119584      s9   Mon Sep 07 06 11 53 EDT 2015   id 831698120392      s10  2015 09 07 10 11 53   id 831698121312   s11  2015 09 07 06 11 53 EDT   id 831698122256     sdf2 and sdfLocal2 include time zone  so we can see what is really going on  s1  amp  s2 are at 06 11 53 in zone EDT   s3  amp  s4 are at 10 11 53 in zone GMT -- equivalent to the original EDT time  Imagine we save s3 or s4 in a data base  where we are using GMT for consistency  so we can have times from anywhere in the world  without storing different time zones   s5 parses the GMT time  but treats it as a local time  So it says  10 11 53  -- the GMT time -- but thinks it is 10 11 53 in local time  Not good   s7 parses the GMT time  but ignores the GMT in the string  so still treats it as a local time   s8 works  because now we include GMT in the string  and the local zone parser uses it to convert from one time zone to another   Now suppose you don t want to store the zone  you want to be able to parse s3  but display it as a local time  The answer is to parse using the same time zone it was stored in -- so use the same sdf as it was created in  sdfGMT1  s9  s10   amp  s11 are all representations of the original time  They are all  correct   That is  d2    d1  Then it is only a question of how you want to DISPLAY it  If you want to display what is stored in DB -- GMT time -- then you need to format it using a GMT sdf  Ths is s10   So here is the final solution  if you don t want to explicitly store with   GMT  in the string  and want to display in GMT format   public static void  testDateFormatting         SimpleDateFormat sdfGMT1   new SimpleDateFormat  yyyy MM dd HH mm ss        sdfGMT1 setTimeZone TimeZone getTimeZone  GMT          try           Date d   new Date            String s3   sdfGMT1 format d              Store s3 in DB                            Retrieve s3 from database  using GMT sdf          Date d2   sdfGMT1 parse s3           String s10   sdfGMT1 format d2         catch  Exception e            e printStackTrace

User · Answer

tl dr     what is the way to retrieve a Date object so that its always in GMT    Instant now      Details  You are using troublesome confusing old date-time classes that are now supplanted by the java time classes   Instant   UTC  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     Instant instant   Instant now        Current moment in UTC    ISO 8601  To exchange this data as text  use the standard ISO 8601 formats exclusively  These formats are sensibly designed to be unambiguous  easy to process by machine  and easy to read across many cultures by people   The java time classes use the standard formats by default when parsing and generating strings   String output   instant toString            2017-01-23T12 34 56 123456789Z   Time zone  If you want to see that same moment as presented in the wall-clock time of a particular region  apply a ZoneId to get a ZonedDateTime   Specify a proper time zone name in the format of continent region  such as America Montreal  Africa Casablanca  or Pacific Auckland  Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones  not standardized  and not even unique       ZoneId z   ZoneId of   Asia Singapore      ZonedDateTime zdt   instant atZone  z         Same simultaneous moment  same point on the timeline    See this code live at IdeOne com   Notice the eight hour difference  as the time zone of Asia Singapore currently has an offset-from-UTC of  08 00  Same moment  different wall-clock time      instant toString    2017-01-23T12 34 56 123456789Z      zdt toString    2017-01-23T20 34 56 123456789 08 00 Asia Singapore    Convert  Avoid the legacy java util Date class  But if you must  you can convert  Look to new methods added to the old classes   java util Date date   Date from  instant          going the other way     Instant instant   myJavaUtilDate toInstant       Date-only  For date-only  use LocalDate   LocalDate ld   zdt toLocalDate         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 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  Java 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 Java 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 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

[java] SimpleDateFormat parse loses timezone

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