Parsing Date in UpperCase to LocalDate

Question

I'm trying to parse the String FEBRUARY 2019 into a LocalDate.

This is my approach:

LocalDate month = LocalDate.parse("FEBRUARY 2019", DateTimeFormatter.ofPattern("MMMM yyyy"));

Or alternatively setting the Locale.US:

LocalDate month = LocalDate.parse("FEBRUARY 2019", DateTimeFormatter.ofPattern("MMMM yyyy", Locale.US));

But all I get is the following exception:

Exception in thread "main" java.time.format.DateTimeParseException: Text 'FEBRUARY 2019' could not be parsed at index 0

Answer 1

Firstly, I'd suggest that the input you've got isn't a date - it's a year and month. So parse to a YearMonth, and then create a LocalDate from that however you want. I find it simplest to make text handling code only deal with text handling, and perform any other conversions separately when you're in the date/time domain already.

To handle the case sensitivity issue, you can create a DateTimeFormatter with case-insensitive parsing. Here's a complete example of that:

import java.time.*;
import java.time.format.*;
import java.util.*;

public class Test {
    public static void main(String[] args) {
        // Note: this would probably be a field somewhere so you don't need
        // to build it every time.
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
            .parseCaseInsensitive()
            .appendPattern("MMMM yyyy")
            .toFormatter(Locale.US);

        YearMonth month = YearMonth.parse("FEBRUARY 2019", formatter);
        System.out.println(month);
    }
}

As an alternative approach which could be of use if you have a different representation, you could build a map and pass that to DateTimeFormatterBuilder.appendText. (I only found this when somehow bungling the code about.)

import java.time.*;
import java.time.format.*;
import java.time.temporal.*;
import java.util.*;

public class Test {
    public static void main(String[] args) {
        // TODO: Build this map up programmatically instead?            
        Map<Long, String> monthNames = new HashMap<>();
        monthNames.put(1L, "JANUARY");
        monthNames.put(2L, "FEBRUARY");
        monthNames.put(3L, "MARCH");
        monthNames.put(4L, "APRIL");
        monthNames.put(5L, "MAY");
        monthNames.put(6L, "JUNE");
        monthNames.put(7L, "JULY");
        monthNames.put(8L, "AUGUST");
        monthNames.put(9L, "SEPTEMBER");
        monthNames.put(10L, "OCTOBER");
        monthNames.put(11L, "NOVEMBER");
        monthNames.put(12L, "DECEMBER");

        // Note: this would probably be a field somewhere so you don't need
        // to build it every time.
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
            .appendText(ChronoField.MONTH_OF_YEAR, monthNames)
            .appendLiteral(' ')
            .appendPattern("yyyy")
            .toFormatter(Locale.US);

        YearMonth month = YearMonth.parse("FEBRUARY 2019", formatter);
        System.out.println(month);
    }
}

Answer 2

As Jon Skeet stated, you don't have a complete date to parse and can use YearMonth. An alternative is to specify a default day.

Instead of the approach to provide a map of months names, you could also simply use a library such as WordUtils to convert your input into the correct format, e.g. as such:

final LocalDate month = LocalDate.parse(
        org.apache.commons.text.WordUtils.capitalizeFully("FEBRUARY 2019"),
        new DateTimeFormatterBuilder()
                    .appendPattern("MMMM uuuu")
                    .parseCaseInsensitive()
                    .parseDefaulting(ChronoField.DAY_OF_MONTH, 1)
                    .toFormatter(Locale.US));