Current time in microseconds in java

Question

On a Unix system  is there a way to get a timestamp with microsecond level accuracy in Java  Something like C s gettimeofday function

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As other posters already indicated  your system clock is probably not synchronized up to microseconds to actual world time  Nonetheless are microsecond precision timestamps useful as a hybrid for both indicating current wall time  and measuring profiling the duration of things   I label all events messages written to a log files using timestamps like  2012-10-21 19 13 45 267128   These convey both when it happened   wall  time   and can also be used to measure the duration between this and the next event in the log file  relative difference in microseconds    To achieve this  you need to link System currentTimeMillis   with System nanoTime   and work exclusively with System nanoTime   from that moment forward  Example code          Class to generate timestamps with microsecond precision    For example  MicroTimestamp INSTANCE get      2012-10-21 19 13 45 267128       public enum MicroTimestamp     INSTANCE       private long              startDate      private long              startNanoseconds      private SimpleDateFormat  dateFormat       private MicroTimestamp         this startDate   System currentTimeMillis           this startNanoseconds   System nanoTime           this dateFormat   new SimpleDateFormat  yyyy-MM-dd HH mm ss SSS              public String get         long microSeconds    System nanoTime   - this startNanoseconds    1000         long date   this startDate    microSeconds 1000          return this dateFormat format date    String format   03d   microSeconds   1000

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a  quick and dirty  solution that I eventually went with   TimeUnit NANOSECONDS toMicros System nanoTime       UPDATE   I originally went with System nanoTime but then I found out it should only be used for elapsed time  I eventually changed my code to work with milliseconds or at some places use   TimeUnit MILLISECONDS toMicros System currentTimeMillis       but this will just add zeros at the end of the value  micros   millis   1000   Left this answer here as a  warning sign  in case someone else thinks of nanoTime

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If you re interested in Linux  If you fish out the source code to  currentTimeMillis     you ll see that  on Linux  if you call this method  it gets a microsecond time back    However Java then truncates the microseconds and hands you back milliseconds   This is partly because Java has to be cross platform so providing methods specifically for Linux was a big no-no back in the day  remember that cruddy soft link support from 1 6 backwards      It s also because  whilst you clock can give you back microseconds in Linux  that doesn t necessarily mean it ll be good for checking the time   At microsecond levels  you need to know that NTP is not realigning your time and that your clock has not drifted too much during method calls   This means  in theory  on Linux  you could write a JNI wrapper that is the same as the one in the System package  but not truncate the microseconds

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Here is an example of how to create an UnsignedLong current Timestamp   UnsignedLong current   new UnsignedLong new Timestamp new Date   getTime    getTime

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No  Java doesn t have that ability   It does have System nanoTime    but that just gives an offset from some previously known time  So whilst you can t take the absolute number from this  you can use it to measure nanosecond  or higher  precision   Note that the JavaDoc says that whilst this provides nanosecond precision  that doesn t mean nanosecond accuracy  So take some suitably large modulus of the return value

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You can use System nanoTime     long start   System nanoTime       do stuff long end   System nanoTime    long microseconds    end - start    1000    to get time in nanoseconds but it is a strictly relative measure  It has no absolute meaning  It is only useful for comparing to other nano times to measure how long something took to do

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If you intend to use it for realtime system  perhaps java isnt the best choice to get the timestamp  But  if youre going to use if for unique key  then Jason Smith s answer will do enough  But just in case  to anticipate 2 item end up getting the same timestamp  its possible if those 2 were processed almost simultaneously   you can loop until the last timestamp not equals with the current timestamp   String timestamp   new String    do       timestamp   String valueOf MicroTimestamp INSTANCE get         item setTimestamp timestamp     while lasttimestamp equals timestamp    lasttimestamp   item getTimestamp

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tl dr  Java 9 and later  Up to nanoseconds resolution when capturing the current moment  That   s 9 digits of decimal fraction   Instant now           2017-12-23T12 34 56 123456789Z   To limit to microseconds  truncate   Instant                   Represent a moment in UTC    now                      Capture the current moment  Returns a  Instant  object    truncatedTo              Lop off the finer part of this moment       ChronoUnit MICROS     Granularity to which we are truncating                             Returns another  Instant  object rather than changing the original  per the immutable objects pattern        2017-12-23T12 34 56 123456Z   In practice  you will see only microseconds captured with  now as contemporary conventional computer hardware clocks are not accurate in nanoseconds    Details  The other Answers are somewhat outdated as of Java 8   java time  Java 8 and later comes with the java time framework  These new classes supplant the flawed troublesome date-time classes shipped with the earliest versions of Java such as java util Date  Calendar and java text SimpleDateFormat  The framework is defined by JSR 310  inspired by Joda-Time  extended by the ThreeTen-Extra project   The classes in java time resolve to nanoseconds  much finer than the milliseconds used by both the old date-time classes and by Joda-Time  And finer than the microseconds asked in the Question     Clock Implementation  While the java time classes support data representing values in nanoseconds  the classes do not yet generate values in nanoseconds  The now   methods use the same old clock implementation as the old date-time classes  System currentTimeMillis    We have the new Clock interface in java time but the implementation for that interface is the same old milliseconds clock    So you could format the textual representation of the result of ZonedDateTime now  ZoneId of   America Montreal      to see nine digits of a fractional second but only the first three digits will have numbers like this      2017-12-23T12 34 56 789000000Z   New Clock In Java 9  The OpenJDK and Oracle implementations of Java 9 have a new default Clock implementation with finer granularity  up to the full nanosecond capability of the java time classes    See the OpenJDK issue  Increase the precision of the implementation of java time Clock systemUTC    That issue has been successfully implemented      2017-12-23T12 34 56 123456789Z   On a MacBook Pro  Retina  15-inch  Late 2013  with macOS Sierra  I get the current moment in microseconds  up to six digits of decimal fraction        2017-12-23T12 34 56 123456Z   Hardware Clock  Remember that even with a new finer Clock implementation  your results may vary by computer  Java depends on the underlying computer hardware   s clock to know the current moment     The resolution of the hardware clocks vary widely  For example  if a particular computer   s hardware clock supports only microseconds granularity  any generated date-time values will have only six digits of fractional second with the last three digits being zeros   The accuracy of the hardware clocks vary widely  Just because a clock generates a value with several digits of decimal fraction of a second  those digits may be inaccurate  just approximations  adrift from actual time as might be read from an atomic clock  In other words  just because you see a bunch of digits to the right of the decimal mark does not mean you can trust the elapsed time between such readings to be true to that minute degree

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You could maybe create a component that determines the offset between System nanoTime   and System currentTimeMillis   and effectively get nanoseconds since epoch   public class TimerImpl implements Timer        private final long offset       private static long calculateOffset             final long nano   System nanoTime            final long nanoFromMilli   System currentTimeMillis     1 000 000          return nanoFromMilli - nano             public TimerImpl             final int count   500          BigDecimal offsetSum   BigDecimal ZERO          for  int i   0  i  lt  count  i                  offsetSum   offsetSum add BigDecimal valueOf calculateOffset                        offset    offsetSum divide BigDecimal valueOf count    longValue               public long nowNano             return offset   System nanoTime               public long nowMicro             return  offset   System nanoTime      1000             public long nowMilli             return System currentTimeMillis              Following test produces fairly good results on my machine        final Timer timer   new TimerImpl        while  true            System out println timer nowNano             System out println timer nowMilli             The difference seems to oscillate in range of  -3ms  I guess one could tweak the offset calculation a bit more   1495065607202174413 1495065607203 1495065607202177574 1495065607203     1495065607372205730 1495065607370 1495065607372208890 1495065607370

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Use Instant to compute microseconds since Epoch   val instant   Instant now    val currentTimeMicros   instant getEpochSecond     1000 000   instant getNano     1000

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LocalDateTime now   truncatedTo ChronoUnit MICROS

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Java support microseconds through TimeUnit enum   Here is the java doc  Enum TimeUnit  You can get microseconds in java by this way   long microsenconds   TimeUnit MILLISECONDS toMicros System currentTimeMillis       You also can convert microseconds back to another time units  for example   long seconds   TimeUnit MICROSECONDS toSeconds microsenconds

[java] Current time in microseconds in java

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