Formatting Java Date and Time in Millis

Question

What's a clean, modern way of formatting Java Date and Time from System.currentTimeInMillis() so that the formatting is as follows:

• For Date: YYYY-MM-DD
• For Time: HH-MM-SS-mmmm, where HH is a 2-digit hour, MM is a 2-digit minute, SS is a 2-digit second, and mmm is a 3-digit millisecond

Looking to get the formatting Date/Time of the current instant (now). Something like:

long current = System.currentTimeInMillis();
String formattedDate = getFormattedDateFromCurrent(current);
String formattedTime = getFormattedTimeFromCurrent(current);

Don't know if raw Java can do this, or if I have to switch over to something like joda-time. Thanks in advance!

Answer 1

You can just pass the long value to the Date constructor and it will give you the date.

You can then format this date to get you desired format.

Code to convert to date -

long tmp = 1018021774496l;  
Date d = new Date(tmp);  
System.out.println(d); 

Have a look here. Its the first result in Google ;)

Answer 2

SimpleDateFormat is a common tool for formatting date/time in Java. You just need to specify the pattern that you want to represent the date/time.

Date now = new Date();
// or you can use
// long millis = System.currentTimeInMillis();
// Date now = new Date(millis);

String datePattern = "yyyy-mm-dd HH-MM-SS";
SimpleDateFormat formatter = new SimpleDateFormat(datePattern);
String formattedDate = formatter.format(now);

Answer 3

tl;dr

OffsetDateTime.now( ZoneOffset.UTC ).toLocalDate().toString()

2016-01-23

…and…

OffsetDateTime.now( ZoneOffset.UTC ).toLocalTime().toString()

12:34:56.789

Using java.time

The “clean, modern way” would be using java.time classes.

No need to call System.currentTimeInMillis(). The java.time classes can capture the current moment.

If you want the current moment in UTC, use an Instant.

Instant instant = Instant.now();

For formatting, morph that into the more flexible OffsetDateTime.

OffsetDateTime odt = instant.atOffset( ZoneOffset.UTC );

To generate strings, you could define a DateTimeFormatter object. But in your case, the desired output happens to conform to the standard ISO 8601 formats used by default in the java.time classes.

So, for the date-only portion, use a LocalDate. For time-of-day portion, LocalTime. Call their toString methods.

String dateOnly = odt.toLocalDate().toString();
String timeOnly = odt.toLocalTime().toString();

Resolution

Note that while java.time classes resolve to nanoseconds, capturing the current moment in Java 8 is limited to milliseconds. In Java 9, a new implementation of Clock provides capturing the current moment in nanoseconds (or as best your computer clock hardware can provide).

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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?

• Java SE 8 and SE 9 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 SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • 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.