DateTimeFormatTest.java

import org.junit.Test;

import java.text.DateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

import static org.junit.Assert.assertEquals;

public class DateTimeFormatTest {

    static Date makeDateTime(TimeZone timeZone, int year, int month, int day, int hour, int minute) {
        Calendar calendar = Calendar.getInstance(timeZone); // need timezone to correctly interpret input numbers
        calendar.setTimeInMillis(0L);                       // just to zero seconds and milliseconds
        calendar.set(year, month - 1, day, hour, minute);   // calendar months start from zero
        return calendar.getTime();                          // here we get only the long number
    }

    static long makeTimestamp(TimeZone timeZone, int year, int month, int day, int hour, int minute) {
        Calendar calendar = Calendar.getInstance(timeZone); // need timezone to correctly interpret input numbers
        calendar.setTimeInMillis(0L);                       // just to zero seconds and milliseconds
        calendar.set(year, month - 1, day, hour, minute);   // calendar months start from zero
        return calendar.getTimeInMillis();                  // here we get only the long number
    }

    static String formatDateTime(Date dateTime, TimeZone timeZone, Locale locale, int dateStyle, int timeStyle) {
        DateFormat format = DateFormat.getDateTimeInstance(dateStyle, timeStyle, locale);
        format.setTimeZone(timeZone);                       // timezone makes sense again
        return format.format(dateTime);
    }

    static String formatDateTime(Date dateTime, TimeZone timeZone, Locale locale) {
        return formatDateTime(dateTime, timeZone, locale, DateFormat.LONG, DateFormat.LONG);
    }

    static String formatDateTime(Date dateTime, TimeZone timeZone) {
        return formatDateTime(dateTime, timeZone, Locale.US);
    }

    static String formatTimestamp(long timestamp, TimeZone timeZone, Locale locale, int dateStyle, int timeStyle) {
        DateFormat format = DateFormat.getDateTimeInstance(dateStyle, timeStyle, locale);
        format.setTimeZone(timeZone);                       // timezone makes sense again
        return format.format(new Date(timestamp));          // Date is just a timestamp
    }

    static String formatTimestamp(long timestamp, TimeZone timeZone, Locale locale) {
        return formatTimestamp(timestamp, timeZone, locale, DateFormat.LONG, DateFormat.LONG);
    }

    static String formatTimestamp(long timestamp, TimeZone timeZone) {
        return formatTimestamp(timestamp, timeZone, Locale.US);
    }

    @Test
    public void testMakeDateTime() {
        Date epoch = makeDateTime(TimeZone.getTimeZone("UTC"), 1970, 1, 1, 0, 0);
        assertEquals(0L, epoch.getTime());
        Date happydev = makeDateTime(TimeZone.getTimeZone("Asia/Omsk"), 2015, 12, 5, 10, 20);
        assertEquals(1449289200000L, happydev.getTime());
    }

    @Test
    public void testFormatDateTime() {
        Date epoch = makeDateTime(TimeZone.getTimeZone("UTC"), 1970, 1, 1, 0, 0);
        assertEquals("January 1, 1970 12:00:00 AM UTC", formatDateTime(epoch, TimeZone.getTimeZone("UTC")));
        assertEquals("January 1, 1970 6:00:00 AM OMST", formatDateTime(epoch, TimeZone.getTimeZone("Asia/Omsk")));
        assertEquals("December 31, 1969 7:00:00 PM EST", formatDateTime(epoch, TimeZone.getTimeZone("EST")));
        Date happydev = makeDateTime(TimeZone.getTimeZone("Asia/Omsk"), 2015, 12, 5, 10, 20);
        assertEquals("December 5, 2015 4:20:00 AM UTC", formatDateTime(happydev, TimeZone.getTimeZone("UTC")));
        assertEquals("December 5, 2015 10:20:00 AM OMST", formatDateTime(happydev, TimeZone.getTimeZone("Asia/Omsk")));
        assertEquals("December 4, 2015 11:20:00 PM EST", formatDateTime(happydev, TimeZone.getTimeZone("EST")));
    }

    @Test
    public void testMakeTimestamp() {
        long epoch = makeTimestamp(TimeZone.getTimeZone("UTC"), 1970, 1, 1, 0, 0);
        assertEquals(0L, epoch);
        long happydev = makeTimestamp(TimeZone.getTimeZone("Asia/Omsk"), 2015, 12, 5, 10, 20);
        assertEquals(1449289200000L, happydev);
    }

    @Test
    public void testFormatTimestamp() {
        long epoch = makeTimestamp(TimeZone.getTimeZone("UTC"), 1970, 1, 1, 0, 0);
        assertEquals("January 1, 1970 12:00:00 AM UTC", formatTimestamp(epoch, TimeZone.getTimeZone("UTC")));
        assertEquals("January 1, 1970 6:00:00 AM OMST", formatTimestamp(epoch, TimeZone.getTimeZone("Asia/Omsk")));
        assertEquals("December 31, 1969 7:00:00 PM EST", formatTimestamp(epoch, TimeZone.getTimeZone("EST")));
        long happydev = makeTimestamp(TimeZone.getTimeZone("Asia/Omsk"), 2015, 12, 5, 10, 20);
        assertEquals("December 5, 2015 4:20:00 AM UTC", formatTimestamp(happydev, TimeZone.getTimeZone("UTC")));
        assertEquals("December 5, 2015 10:20:00 AM OMST", formatTimestamp(happydev, TimeZone.getTimeZone("Asia/Omsk")));
        assertEquals("December 4, 2015 11:20:00 PM EST", formatTimestamp(happydev, TimeZone.getTimeZone("EST")));
    }

}