Java 8 ZonedDateTime format date

Question

I am writing a code to get current date of British Summer Time. I am stuck in converting the date in desired format using below code.

ZoneId zid = ZoneId.of("Europe/London");      
ZonedDateTime lt = ZonedDateTime.now(zid); 


// create a formatter
DateTimeFormatter formatter = DateTimeFormatter.ISO_DATE;
// apply format()
String value = lt.format(formatter);

System.out.println("value ="+value);

I am getting the output as value =2020-06-01+02:00 which is fine as per written code. But I want output of format 01-JUN-20

What formatter shall I use to achieve this? Also will 'Europe/London' give proper date while in DST & also while not in DST? please help me in above 2 questions.

Answer 1

tl;dr

ZonedDateTime
.now(
    ZoneId.of( "Europe/London" )
)
.format(
    DateTimeFormatter
    .ofPattern( "dd-MMM-uu" )
    .withLocale( Locale.UK )
)
.toUpperCase(
    Locale.UK
)

See this code run live at IdeOne.com .

01-JUN-20

Details

You asked:

will 'Europe/London' give proper date while in DST & also while not in DST?

Yes, your code is correct. Passing a ZoneId to ZonedDateTime.now does account for any anomalies in wall-clock time, including the anomaly of Daylight Saving Time (DST) . The result is a date and time-of-day as seen by people in that region when they look up at the calendar & clock on their respective wall.

You may find it interesting or useful to see that same moment in UTC , an offset from UTC of zero hours-minutes-seconds. Extract a Instant object by calling toInstant .

You said:

But I want output of format 01-JUN-20

Define a custom formatting pattern to match your desired output. Instantiate a DateTimeFormatter object.

Specify a Locale object to determine the human language and cultural norms in naming and abbreviating the month name.

Locale locale = Locale.UK ;  // Or Locale.US, etc.
DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd-MMM-uu" ).withLocale( locale ) ;
String output = myZonedDateTime.format( f ) ;

I do not know how to force all-uppercase in a DateTimeFormatter formatting pattern. Perhaps DateTimeFormatterBuilder might help; I don't know. As a workaround, you could simply call String.toUpperCase( Locale ) .

Locale locale = Locale.US ;  // Or Locale.UK, etc.
DateTimeFormatter f = DateTimeFormatter.ofPattern( "dd-MMM-uu" ).withLocale( locale ) ;
String output = myZonedDateTime.format( f ).toUpperCase( locale ) ;

Tips

• I suggest you not hard-code a format such as that. Generally better to let java.time automatically localize for you by calling DateTimeFormatter.ofLocalizedDateTime .
• And I further suggest avoiding the use of only two digits for year as that makes the output harder to read and creates ambiguity. Saving a few pixels or toner particles does not justify the confusion I have seen occur in businesses.
• Consider using the standard ISO 8601 format for dates, if your users are amenable: YYYY-MM-DD. This format is easy to recognize, easy to process mentally (large-medium-small level of detail), and easy to read across cultures. The ISO 8601 formats are used by default in the java.time classes when generating/parsing text.