How to convert ZonedDateTime to Date

Question

I am trying to set a server agnostic date time in my database and I believe the best practice to do so is to set a UTC DateTime  My db server is Cassandra and the db driver for Java understands only the Date type   So assuming that in my code I am using the new Java 8 ZonedDateTime to get the UTC now  ZonedDateTime now ZoneOffset UTC    how can I convert this ZonedDateTime instance to the  legacy  Date class

User · Answer

If you are interested in now only  then simply use   Date d   new Date

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You can convert ZonedDateTime to an instant  which you can use directly with Date   Date from java time ZonedDateTime now   toInstant

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If you are using the ThreeTen backport for Android and can t use the newer Date from Instant instant   which requires minimum of API 26  you can use   ZonedDateTime zdt   ZonedDateTime now    Date date   new Date zdt toInstant   toEpochMilli       or   Date date   DateTimeUtils toDate zdt toInstant       Please also read the advice in Basil Bourque s answer

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The accepted answer did not work for me  The Date returned is always the local Date and not the Date for the original Time Zone  I live in UTC 2     This did not work for me Date from java time ZonedDateTime now   toInstant        I have come up with two alternative ways to get the correct Date from a ZonedDateTime    Say you have this ZonedDateTime for Hawaii  LocalDateTime ldt   LocalDateTime now    ZonedDateTime zdt   ldt atZone ZoneId of  US Hawaii       UTC-10   or for UTC as asked originally  Instant zulu   Instant now       GMT  UTC 0 ZonedDateTime zdt   zulu atZone ZoneId of  UTC       Alternative 1  We can use java sql Timestamp  It is simple but it will probably also make a dent in your programming integrity  Date date1   Timestamp valueOf zdt toLocalDateTime       Alternative 2  We create the Date from millis  answered here earlier   Note that local ZoneOffset is a must   ZoneOffset localOffset   ZoneOffset systemDefault   getRules   getOffset LocalDateTime now     long zonedMillis   1000L   zdt toLocalDateTime   toEpochSecond localOffset    zdt toLocalDateTime   getNano     1000000L  Date date2   new Date zonedMillis

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For a docker application like beehuang commented you should set your timezone   Alternatively you can use withZoneSameLocal  For example   2014-07-01T00 00 02 00 GMT 02 00  is converted by  Date from zonedDateTime withZoneSameLocal ZoneId systemDefault    toInstant      to Tue Jul 01 00 00 00 CEST 2014 and by  Date from zonedDateTime toInstant      to Mon Jun 30 22 00 00 UTC 2014

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tl dr  java util Date from      Transfer the moment in UTC  truncating any microseconds or nanoseconds to milliseconds      Instant now          Capture current moment in UTC  with resolution as fine as nanoseconds      Though there was no point in that code above  Both java util Date and Instant represent a moment in UTC  always in UTC  Code above has same effect as   new java util Date       Capture current moment in UTC    No benefit here to using ZonedDateTime  If you already have a ZonedDateTime  adjust to UTC by extracting a Instant   java util Date from                 Truncates any micros nanos      myZonedDateTime toInstant       Adjust to UTC  Same moment  same point on the timeline  different wall-clock time      Other Answer Correct  The Answer by ssoltanid correctly addresses your specific question  how to convert a new-school java time object  ZonedDateTime  to an old-school java util Date object  Extract the Instant from the ZonedDateTime and pass to java util Date from      Data Loss  Note that you will suffer data loss  as Instant tracks nanoseconds since epoch while java util Date tracks milliseconds since epoch     Your Question and comments raise other issues   Keep Servers In UTC  Your servers should have their host OS set to UTC as a best practice generally  The JVM picks up on this host OS setting as its default time zone  in the Java implementations that I m aware of   Specify Time Zone  But you should never rely on the JVM   s current default time zone  Rather than pick up the host setting  a flag passed when launching a JVM can set another time zone  Even worse  Any code in any thread of any app at any moment can make a call to java util TimeZone  setDefault to change that default at runtime   Cassandra Timestamp Type  Any decent database and driver should automatically handle adjusting a passed date-time to UTC for storage  I do not use Cassandra  but it does seem to have some rudimentary support for date-time  The documentation says its Timestamp type is a count of milliseconds from the same epoch  first moment of 1970 in UTC     ISO 8601  Furthermore  Cassandra accepts string inputs in the ISO 8601 standard formats  Fortunately  java time uses ISO 8601 formats as its defaults for parsing generating strings  The Instant class    toString implementation will do nicely    Precision  Millisecond vs Nanosecord  But first we need to reduce the nanosecond precision of ZonedDateTime to milliseconds  One way is to create a fresh Instant using milliseconds  Fortunately  java time has some handy methods for converting to and from milliseconds   Example Code  Here is some example code in Java 8 Update 60   ZonedDateTime zdt   ZonedDateTime now  ZoneId of   America Montreal           Instant instant   zdt toInstant    Instant instantTruncatedToMilliseconds   Instant ofEpochMilli  instant toEpochMilli      String fodderForCassandra   instantTruncatedToMilliseconds toString        Example  2015-08-18T06 36 40 321Z   Or according to this Cassandra Java driver doc  you can pass a java util Date instance  not to be confused with java sqlDate   So you could make a j u Date from that instantTruncatedToMilliseconds in the code above   java util Date dateForCassandra   java util Date from  instantTruncatedToMilliseconds      If doing this often  you could make a one-liner   java util Date dateForCassandra   java util Date from  zdt toInstant        But it would be neater to create a little utility method   static public java util Date toJavaUtilDateFromZonedDateTime   ZonedDateTime zdt         Instant instant   zdt toInstant           Data-loss  going from nanosecond resolution to milliseconds      java util Date utilDate   java util Date from  instant         return utilDate      Notice the difference in all this code than in the Question  The Question   s code was trying to adjust the time zone of the ZonedDateTime instance to UTC  But that is not necessary  Conceptually      ZonedDateTime   Instant   ZoneId   We just extract the Instant part  which is already in UTC  basically in UTC  read the class doc for precise details           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   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  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   Later versions of Android bundle implementations of the java time classes  For earlier Android   lt 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

User · Answer

Here is an example converting current system time to UTC  It involves formatting ZonedDateTime as a String and then the String object will be parsed into a date object using java text DateFormat             ZonedDateTime zdt   ZonedDateTime now ZoneOffset UTC       final DateTimeFormatter DATETIME FORMATTER   DateTimeFormatter ofPattern  yyyyMMdd HH mm ss        final DateFormat FORMATTER YYYYMMDD HH MM SS   new SimpleDateFormat  yyyyMMdd HH mm ss        String dateStr   zdt format DATETIME FORMATTER        Date utcDate   null      try           utcDate   FORMATTER YYYYMMDD HH MM SS parse dateStr        catch  ParseException ex           ex printStackTrace

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I use this      public class TimeTools        public static Date getTaipeiNowDate             Instant now   Instant now            ZoneId zoneId   ZoneId of  Asia Taipei            ZonedDateTime dateAndTimeInTai   ZonedDateTime ofInstant now  zoneId           try               return new SimpleDateFormat  yyyy-MM-dd HH mm ss   parse dateAndTimeInTai toString   substring 0  19  replace  T                    catch  ParseException e                   TODO Auto-generated catch block             e printStackTrace                      return null            Because  Date from java time ZonedDateTime ofInstant now  zoneId  toInstant      It s not work    If u run your application in your computer  it s not problem  But if you run in any region of AWS or Docker or GCP  it will generate problem  Because computer is not your timezone on Cloud  You should set your correctly timezone in Code  For example  Asia Taipei  Then it will correct in AWS or Docker or GCP   public class App       public static void main String   args            Instant now   Instant now            ZoneId zoneId   ZoneId of  Australia Sydney            ZonedDateTime dateAndTimeInLA   ZonedDateTime ofInstant now  zoneId           try               Date ans   new SimpleDateFormat  yyyy-MM-dd HH mm ss   parse dateAndTimeInLA toString   substring 0  19  replace  T                      System out println  ans   ans             catch  ParseException e                      Date wrongAns   Date from java time ZonedDateTime ofInstant now  zoneId  toInstant             System out println  wrongAns   wrongAns

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You can do this using the java time classes built into Java 8 and later   ZonedDateTime temporal       long epochSecond   temporal getLong INSTANT SECONDS   int nanoOfSecond   temporal get NANO OF SECOND   Date date   new Date epochSecond   1000   nanoOfSecond   1000000

[java] How to convert ZonedDateTime to Date?

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