How to convert two digit year to full year using Java 8 time API

Question

I wish to remove the Joda-Time library from my project.

I am trying to convert a two digit year to full year. The following code from Joda-Time can fulfil the purpos

Answer 1

Why it didn’t work

java.time doesn’t supply default values for month and day of month the way it seems that Joda-Time does. The message says that it cannot obtain a LocalDate from a year alone, or conversely, it is missing month and day (you may supply your own default values, though, as demonstrated in Mikhail Kholodkov’s answer). Generally this behaviour is here to help us: it reminds us to supply all the values needed, and makes it clear from the code if any default values are used, and which.

What to do instead

Just use the Year class of java.time. First declare

public static final DateTimeFormatter TWO_YEAR_FORMATTER = new DateTimeFormatterBuilder()
        .appendValueReduced(ChronoField.YEAR, 2, 2, 1950)
        .toFormatter();

Then use

    int year = Year.parse("99", TWO_YEAR_FORMATTER).getValue();
    System.out.println(year);

Output

1999

Insert your desired base value where I put 1950 to specify a year within 99 years (inclusive) from that year. If you want the year to be in the past including this year, you may use:

private static final Year base = Year.now(ZoneId.of("Asia/Kolkata")).minusYears(99);
public static final DateTimeFormatter TWO_YEAR_FORMATTER = new DateTimeFormatterBuilder()
        .appendValueReduced(ChronoField.YEAR, 2, 2, base.getValue())
        .toFormatter();

BTW, don’t take my word for it, but I think Joda-Time uses current year minus 30 years as base or pivot. If this is so, using 30 instead of 99 in the last snippet will be the most compatible (so will also give you the 1999 you expected).