How to get milliseconds from LocalDateTime in Java 8

Question

I am wondering if there is a way to get current milliseconds since 1-1-1970  epoch  using the new LocalDate  LocalTime or LocalDateTime classes of Java 8   The known way is below     long currentMilliseconds   new Date   getTime      or  long currentMilliseconds   System currentTimeMillis

User · Answer

What I do so I don t specify a time zone is   System out println  ldt     LocalDateTime now   atZone ZoneId systemDefault    toInstant   toEpochMilli     System out println  ctm     System currentTimeMillis       gives   ldt 1424812121078  ctm 1424812121281   As you can see the numbers are the same except for a small execution time   Just in case you don t like System currentTimeMillis  use Instant now   toEpochMilli

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default LocalDateTime getDateFromLong long timestamp        try           return LocalDateTime ofInstant Instant ofEpochMilli timestamp   ZoneOffset UTC         catch  DateTimeException tdException              throw new           default Long getLongFromDateTime LocalDateTime dateTime        return dateTime atOffset ZoneOffset UTC  toInstant   toEpochMilli

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Why didn t anyone mentioned the method LocalDateTime toEpochSecond     LocalDateTime localDateTime          whatever e g  LocalDateTime now   long time2epoch   localDateTime toEpochSecond ZoneOffset UTC     This seems way shorter that many suggested answers above

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You can use java sql Timestamp also to get milliseconds   LocalDateTime now   LocalDateTime now    long milliSeconds   Timestamp valueOf now  getTime    System out println  MilliSeconds    milliSeconds

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To get the current time in milliseconds  since the epoch   use System currentTimeMillis

User · Answer

I m not entirely sure what you mean by  current milliseconds  but I ll assume it s the number of milliseconds since the  epoch   namely midnight  January 1  1970 UTC   If you want to find the number of milliseconds since the epoch right now  then use System currentTimeMillis   as Anubian Noob has pointed out  If so  there s no reason to use any of the new java time APIs to do this   However  maybe you already have a LocalDateTime or similar object from somewhere and you want to convert it to milliseconds since the epoch  It s not possible to do that directly  since the LocalDateTime family of objects has no notion of what time zone they re in  Thus time zone information needs to be supplied to find the time relative to the epoch  which is in UTC   Suppose you have a LocalDateTime like this   LocalDateTime ldt   LocalDateTime of 2014  5  29  18  41  16     You need to apply the time zone information  giving a ZonedDateTime  I m in the same time zone as Los Angeles  so I d do something like this   ZonedDateTime zdt   ldt atZone ZoneId of  America Los Angeles       Of course  this makes assumptions about the time zone  And there are edge cases that can occur  for example  if the local time happens to name a time near the Daylight Saving Time  Summer Time  transition  Let s set these aside  but you should be aware that these cases exist   Anyway  if you can get a valid ZonedDateTime  you can convert this to the number of milliseconds since the epoch  like so   long millis   zdt toInstant   toEpochMilli

User · Answer

To avoid ZoneId you can do   LocalDateTime date   LocalDateTime of 1970  1  1  0  0    System out println  Initial Epoch  TimeInMillis       date toInstant ZoneOffset ofTotalSeconds 0   toEpochMilli       Getting 0 as value  that s right

User · Answer

If you have a Java 8 Clock  then you can use clock millis    although it recommends you use clock instant   to get a Java 8 Instant  as it s more accurate    Why would you use a Java 8 clock  So in your DI framework you can create a Clock bean    Bean public Clock getClock         return Clock systemUTC        and then in your tests you can easily Mock it    MockBean private Clock clock    or you can have a different bean    Bean public Clock getClock         return Clock fixed instant  zone       which helps with tests that assert dates and times immeasurably

User · Answer

Since Java 8 you can call java time Instant toEpochMilli      For example the call  final long currentTimeJava8   Instant now   toEpochMilli      gives you the same results as  final long currentTimeJava1   System currentTimeMillis

User · Answer

Date and time as String to Long  millis   String dateTimeString    quot 2020-12-12T14 34 18 000Z quot    DateTimeFormatter formatter   DateTimeFormatter                  ofPattern  quot yyyy-MM-dd T HH mm ss SSS Z  quot   Locale ENGLISH    LocalDateTime localDateTime   LocalDateTime          parse dateTimeString  formatter    Long dateTimeMillis   localDateTime          atZone ZoneId systemDefault             toInstant            toEpochMilli

User · Answer

You can try this  long diff   LocalDateTime now   atZone ZoneOffset UTC  toInstant   toEpochMilli

[java] How to get milliseconds from LocalDateTime in Java 8

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