Java - Date format for Multiple Scenarios

Question

I have a java component to format the date that I retrieve. Here is my code:

    Format formatter      = new SimpleDateFormat(\"yyyyMMdd\");
        String s = \         


        

Answer 1

In case of you have optional parts in pattern you can use [ and ].

For example

public static Instant toInstant(final String timeStr){
    final DateTimeFormatter formatter = DateTimeFormatter
            .ofPattern("yyyy-MM-dd HH[:mm[:ss[ SSSSSSSS]]]")
            .withZone(ZoneId.of("UTC"));
    try {
        return Instant.from(formatter.parse(timeStr));
    }catch (DateTimeException e){
        final DateTimeFormatter formatter2 = DateTimeFormatter
                .ofPattern("yyyy-MM-dd")
                .withZone(ZoneId.of("UTC"));
        return LocalDate.parse(timeStr, formatter2).atStartOfDay().atZone(ZoneId.of("UTC")).toInstant();
    }
}

cover

• yyyy-MM-dd
• yyyy-MM-dd HH
• yyyy-MM-dd HH:mm
• yyyy-MM-dd HH:mm:ss
• yyyy-MM-dd HH:mm:ss SSSSSSSS

Answer 2

Different types

String s = "2019-04-23 06:57:00";

String s = "2019-04-23";

These are two different kinds of information. One is a date with time-of-day, the other is simply a date. So you should be parsing each as different types of objects.

LocalDateTime.parse

To comply with the ISO 8601 standard format used by default in the LocalDateTime class, replace the SPACE in the middle with a T. I suggest you educate the publisher of your data about using only ISO 8601 formats when exchanging date-time values as text.

LocalDateTime ldt1 = LocalDateTime.parse( "2019-04-23 06:57:00".replace( " " , "T" ) ) ;

The fractional second parses by default as well.

LocalDateTime ldt2 = LocalDateTime.parse( "2019-04-23 06:57:00.0".replace( " " , "T" ) ) ;

See this code run live at IdeOne.com.

ldt1.toString(): 2019-04-23T06:57

ldt2.toString(): 2019-04-23T06:57

LocalDate.parse

Your date-only input already complies with ISO 8601.

LocalDate ld = LocalDate.parse( "2019-04-23" ) ;

See this code run live at IdeOne.com.

ld.toString(): 2019-04-23

Date with time-of-day

You can strip out the time-of-day from the date.

LocalDate ld = ldt.toLocalDate() ;

And you can add it back in.

LocalTime lt = LocalTime.parse( "06:57:00" ) ;
LocalDateTime ldt = ld.with( lt ) ;

Moment

However, be aware that a LocalDateTime does not represent a moment, is not a point on the timeline. Lacking the context of a time zone or offset-from-UTC, a LocalDateTime cannot hold a moment, as explained in its class JavaDoc.

For a moment, use the ZonedDateTime, OffsetDateTime, or Instant classes. Teach the publisher of your data to include the offset, preferably in UTC.

Avoid legacy date-time classes

The old classes SimpleDateFormat, Date, and Calendar are terrible, riddled with poor design choices, written by people not skilled in date-time handling. These were supplanted years ago by the modern java.time classes defined in JSR 310.