How to convert a date to milliseconds

Question

I want to convert String myDate    2014 10 29 18 10 45  to  long ms  i e  currentinmlilies   I look for it on Google  but I can only find how to convert ms to date    Note  To make it clear  I want to get the ms from the date in 1970 1 1 format

User · Answer

The SimpleDateFormat class allows you to parse a String into a java.util.Date object. Once you have the Date object, you can get the milliseconds since the epoch by calling Date.getTime().

The full example:

String myDate = "2014/10/29 18:10:45";
//creates a formatter that parses the date in the given format
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Date date = sdf.parse(myDate);
long timeInMillis = date.getTime();

Note that this gives you a long and not a double, but I think that's probably what you intended. The documentation for the SimpleDateFormat class has tons on information on how to set it up to parse different formats.

User · Answer

The 2017 answer is  Use the date and time classes introduced in Java 8  and also backported to Java 6 and 7 in the ThreeTen Backport    If you want to interpret the date-time string in the computer   s time zone       long millisSinceEpoch   LocalDateTime parse myDate  DateTimeFormatter ofPattern  uuuu MM dd HH mm ss                 atZone ZoneId systemDefault                 toInstant                toEpochMilli      If another time zone  fill that zone in instead of ZoneId systemDefault    If UTC  use      long millisSinceEpoch   LocalDateTime parse myDate  DateTimeFormatter ofPattern  uuuu MM dd HH mm ss                 atOffset ZoneOffset UTC               toInstant                toEpochMilli

User · Answer

You don t have a Date  you have a String representation of a date  You should convert the String into a Date and then obtain the milliseconds  To convert a String into a Date and vice versa you should use SimpleDateFormat class   Here s an example of what you want need to do  assuming time zone is not involved here    String myDate    2014 10 29 18 10 45   SimpleDateFormat sdf   new SimpleDateFormat  yyyy MM dd HH mm ss    Date date   sdf parse myDate   long millis   date getTime      Still  be careful because in Java the milliseconds obtained are the milliseconds between the desired epoch and 1970-01-01 00 00 00     Using the new Date Time API available since Java 8   String myDate    2014 10 29 18 10 45   LocalDateTime localDateTime   LocalDateTime parse myDate      DateTimeFormatter ofPattern  yyyy MM dd HH mm ss           With this new Date Time API  when using a date  you need to   specify the Zone where the date time will be used  For your case    seems that you want need to use the default zone of your system    Check which zone you need to use for specific behaviour e g    CET or America Lima    long millis   localDateTime      atZone ZoneId systemDefault         toInstant   toEpochMilli

User · Answer

tl dr  LocalDateTime parse               Parse into an object representing a date with a time-of-day but without time zone and without offset-from-UTC       2014 10 29 18 10 45          Convert input string to comply with standard ISO 8601 format       replace         T            Replace SPACE in the middle with a  T        replace         -            Replace SLASH in the middle with a  -      atZone                           Apply a time zone to provide the context needed to determine an actual moment      ZoneId of   Europe Oslo       Specify the time zone you are certain was intended for that input                                    Returns a  ZonedDateTime  object   toInstant                        Adjust into UTC   toEpochMilli                     Get the number of milliseconds since first moment of 1970 in UTC  1970-01-01T00 00Z       1414602645000   Time Zone  The accepted answer is correct  except that it ignores the crucial issue of time zone  Is your input string 6 10 PM in Paris or Montr  al  Or UTC   Use a proper time zone name  Usually a continent plus city region  For example   Europe Oslo   Avoid the 3 or 4 letter codes which are neither standardized nor unique    java time  The modern approach uses the java time classes   Alter your input to conform with the ISO 8601 standard  Replace the SPACE in the middle with a T  And replace the slash characters with hyphens  The java time classes use these standard formats by default when parsing generating strings  So no need to specify a formatting pattern   String input    2014 10 29 18 10 45  replace         T    replace         -      LocalDateTime ldt   LocalDateTime parse  input       A LocalDateTime  like your input string  lacks any concept of time zone or offset-from-UTC  Without the context of a zone offset  a LocalDateTime has no real meaning  Is it 6 10 PM in India  Europe  or Canada  Each of those places experience 6 10 PM at different moments  at different points on the timeline  So you must specify which you have in mind if you want to determine a specific point on the timeline    ZoneId z   ZoneId of   Europe Oslo      ZonedDateTime zdt   ldt atZone  z         Now we have a specific moment  in that ZonedDateTime  Convert to UTC by extracting a 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     Instant instant   zdt toInstant       Now we can get your desired count of milliseconds since the epoch reference of first moment of 1970 in UTC  1970-01-01T00 00Z    long millisSinceEpoch   instant toEpochMilli        Be aware of possible data loss  The Instant object is capable of carrying microseconds or nanoseconds  finer than milliseconds  That finer fractional part of a second will be ignored when getting a count of milliseconds     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     Joda-Time  Update  The Joda-Time project is now in maintenance mode  with the team advising migration to the java time classes  I will leave this section intact for history   Below is the same kind of code but using the Joda-Time 2 5 library and handling time zone    The java util Date   Calendar  and  SimpleDateFormat classes are notoriously troublesome  confusing  and flawed  Avoid them  Use either Joda-Time or the java time package  inspired by Joda-Time  built into Java 8   ISO 8601  Your string is almost in ISO 8601 format  The slashes need to be hyphens and the SPACE in middle should be replaced with a T  If we tweak that  then the resulting string can be fed directly into constructor without bothering to specify a formatter  Joda-Time uses ISO 8701 formats as it s defaults for parsing and generating strings   Example Code  String inputRaw    2014 10 29 18 10 45   String input   inputRaw replace        -    replace        T     DateTimeZone zone   DateTimeZone forID   Europe Oslo        Or DateTimeZone UTC DateTime dateTime   new DateTime  input  zone    long millisecondsSinceUnixEpoch   dateTime getMillis

[java] How to convert a date to milliseconds

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