How to parse three numbers to a LocalDate using a Locale?

Question

I am trying to parse three numbers, like [2, 10, 2014] to a LocalDate using the new Java 8 Date and Time API.

All sounds relatively easy, right? Well, perhaps not.
The additional constraint is that I need to take into account the locale, as for example Dutch and American use different date formatting.

The only input I have are the three numbers and the locale, and the output should be a well-formed date, in the form of a LocalDate.

I have figuring that I will be needing the following steps:

1. Obtain a converter from a Locale that can read in three numbers.
2. Using the converter, transform the three numbers into a LocalDate.

I have looked around a bit, especially in the DateTimeFormatter class, but it seems to want to have the day, month and year formats explicitely passed in, which is not an option for me.

How would I convert three numbers (representing the day, month and year in any order) in a LocalDate?

Examples:

Dutch format:

Locale locale = new Locale("nl");
List<String> inputs = Arrays.asList("2", "10", "2014");
//output should equal
LocalDate.of(2014, 10, 2);

American format:

Locale locale = Locale.ENGLISH;
List<String> inputs = Arrays.asList("10", "2", "2014");
//output should equal
LocalDate.of(2014, 10, 2);

Also keep in mind that I am talking about the concept of numbers, but they need to be represented as Strings to also accommodate languages that use other Unicode characters than the digits 0-9 for their numbers.

Answer 1

First create a strings from numbers and then you can use something like

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.FormatStyle;
import java.util.Locale;

public class IntegerDateTest {

    public static void main(String args[]) {
        int[][] dates = {{10, 02, 2014}, {02, 10, 2014}, {2014, 10, 02}};
        Locale[] locales = {Locale.ENGLISH, Locale.FRENCH, Locale.JAPANESE};

        for (int i = 0; i < 3; i++) {
            int[] dateParts = dates[i];
            Locale locale = locales[i];
            String date = String.format("%02d/%02d/%02d", dateParts[0] % 100,
                    dateParts[1] % 100, dateParts[2] % 100);
            System.out.printf("Locale : %s, Str Date : %s,", locale, date);
            DateTimeFormatter df = new DateTimeFormatterBuilder().append(
                    DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT))
                    .toFormatter(locale);
            System.out.printf(" Parsed Date : %s\n",LocalDate.from(df.parse(date)));
        }
    }
}

Output

Locale : en, Str Date : 10/02/14, Parsed Date : 2014-10-02
Locale : fr, Str Date : 02/10/14, Parsed Date : 2014-10-02
Locale : ja, Str Date : 14/10/02, Parsed Date : 2014-10-02

Answer 2

You can first retrieve the pattern relate with particular locale and then access the elements according to it. You can retrieve the pattern associated with particular locale using simpleDateFormat.toPattern()Here is a sample code

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;

public class T {

    public static void main(String[] args) throws ParseException {
        Locale enLocale = Locale.ENGLISH;
        Locale nlLocale = new Locale("nl");         

        List<String> enInput = Arrays.asList("10", "2", "2014");
        List<String> nlInput = Arrays.asList("2", "10", "2014");
        Map<String, Integer> enPositionMap = getPositionMap(enLocale, enInput);
        Map<String, Integer> nlPositionMap = getPositionMap(nlLocale, nlInput);
        System.out.println("EN date " + LocalDate.of(enPositionMap.get("y"), enPositionMap.get("m"), enPositionMap.get("d")));
        System.out.println("NL date " + LocalDate.of(nlPositionMap.get("y"), nlPositionMap.get("m"), nlPositionMap.get("d")));

    }

    public static Map<String, Integer> getPositionMap(Locale locale, List<String> input) {
        final DateFormat dateInstance = DateFormat.getDateInstance(DateFormat.SHORT, locale);

        Map<String, Integer> map = new HashMap<>();

        if (dateInstance instanceof SimpleDateFormat) {
            String pattern = ((SimpleDateFormat) dateInstance).toPattern();
            String separator = String.valueOf(pattern.charAt(1));

            String[] chunks = pattern.split(separator);

            for (int i = 0; i < chunks.length; i++) {
                switch (chunks[i]) {
                    case "M":
                        map.put("m", Integer.parseInt(input.get(i)));
                        break;
                    case "d":
                        map.put("d", Integer.parseInt(input.get(i)));
                        break;
                    case "yy":
                        map.put("y", Integer.parseInt(input.get(i)));
                        break;
                }
            }

        }

        return map;
    }

}