[java] java.util.Date format SSSSSS: if not microseconds what are the last 3 digits?

tl;dr

Instant.now()
       .toString() 

2018-02-02T00:28:02.487114Z

Instant.parse(
    "2018-02-02T00:28:02.487114Z"
)

java.time

The accepted Answer by ppeterka is correct. Your abuse of the formatting pattern results in an erroneous display of data, while the internal value is always limited milliseconds.

The troublesome SimpleDateFormat and Date classes you are using are now legacy, supplanted by the java.time classes. The java.time classes handle nanoseconds resolution, much finer than the milliseconds limit of the legacy classes.

The equivalent to java.util.Date is java.time.Instant. You can even convert between them using new methods added to the old classes.

Instant instant = myJavaUtilDate.toInstant() ;

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).

Capture the current moment in UTC. Java 8 captures the current moment in milliseconds, while a new Clock implementation in Java 9 captures the moment in finer granularity, typically microseconds though it depends on the capabilities of your computer hardware clock & OS & JVM implementation.

Instant instant = Instant.now() ;

Generate a String in standard ISO 8601 format.

String output = instant.toString() ;

2018-02-02T00:28:02.487114Z

To generate strings in other formats, search Stack Overflow for DateTimeFormatter, already covered many times.

To adjust into a time zone other than UTC, use ZonedDateTime.

ZonedDateTime zdt = instant.atZone( ZoneId.of( "Pacific/Auckland" ) ) ;

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, & 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?

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.

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