Android DateUtils for RFC 1123 dates and ISO 8601 dates

DateUtils.java

package org.wta.util;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

public final class DateUtils {

	// RFC 1123 constants
	private static final String RFC_1123_DATE_TIME = "EEE, dd MMM yyyy HH:mm:ss z";

	// ISO 8601 constants
	private static final String ISO_8601_PATTERN_1 = "yyyy-MM-dd'T'HH:mm:ssZ";
	private static final String ISO_8601_PATTERN_2 = "yyyy-MM-dd'T'HH:mm:ss.SSSZ";
	private static final String[] SUPPORTED_ISO_8601_PATTERNS = new String[]{ISO_8601_PATTERN_1,
			ISO_8601_PATTERN_2};
	private static final int TICK_MARK_COUNT = 2;
	private static final int COLON_PREFIX_COUNT = "+00".length();
	private static final int COLON_INDEX = 22;

	/**
	 * Parses a date from the specified RFC 1123-compliant string.
	 *
	 * @param string the string to parse
	 * @return the {@link Date} resulting from the parsing, or null if the string could not be
	 * parsed
	 */
	public static Date parseRfc1123DateTime(String string) {
		try {
			return new SimpleDateFormat(RFC_1123_DATE_TIME, Locale.US).parse(string);
		} catch (ParseException e) {
			return null;
		}
	}

	/**
	 * Formats the specified date to an RFC 1123-compliant string.
	 *
	 * @param date     the date to format
	 * @param timeZone the {@link TimeZone} to use when formatting the date
	 * @return the formatted string
	 */
	public static String formatRfc1123DateTime(Date date, TimeZone timeZone) {
		SimpleDateFormat dateFormat = new SimpleDateFormat(RFC_1123_DATE_TIME, Locale.US);
		if (timeZone != null) {
			dateFormat.setTimeZone(timeZone);
		}
		return dateFormat.format(date);
	}

	/**
	 * Parses a date from the specified ISO 8601-compliant string.
	 *
	 * @param string the string to parse
	 * @return the {@link Date} resulting from the parsing, or null if the string could not be
	 * parsed
	 */
	public static Date parseIso8601DateTime(String string) {
		if (string == null) {
			return null;
		}
		String s = string.replace("Z", "+00:00");
		for (String pattern : SUPPORTED_ISO_8601_PATTERNS) {
			String str = s;
			int colonPosition = pattern.lastIndexOf('Z') - TICK_MARK_COUNT + COLON_PREFIX_COUNT;
			if (str.length() > colonPosition) {
				str = str.substring(0, colonPosition) + str.substring(colonPosition + 1);
			}
			try {
				return new SimpleDateFormat(pattern, Locale.US).parse(str);
			} catch (final ParseException e) {
				// try the next one
			}
		}
		return null;
	}

	/**
	 * Formats the specified date to an ISO 8601-compliant string.
	 *
	 * @param date     the date to format
	 * @param timeZone the {@link TimeZone} to use when formatting the date
	 * @return the formatted string
	 */
	public static String formatIso8601DateTime(Date date, TimeZone timeZone) {
		SimpleDateFormat dateFormat = new SimpleDateFormat(ISO_8601_PATTERN_1, Locale.US);
		if (timeZone != null) {
			dateFormat.setTimeZone(timeZone);
		}
		String formatted = dateFormat.format(date);
		if (formatted != null && formatted.length() > COLON_INDEX) {
			formatted = formatted.substring(0, 22) + ":" + formatted.substring(22);
		}
		return formatted;
	}

	private DateUtils() {
		// hide constructor
	}
}

DateUtilsTest.java

package org.wta.util;

import org.junit.Test;

import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

import static junit.framework.Assert.assertEquals;
import static junit.framework.Assert.assertNull;

public class DateUtilsTest {

	@Test
	public void testParseRfc1123DateTime() throws Exception {
		Calendar cal = Calendar.getInstance();
		cal.clear();
		cal.setTimeZone(TimeZone.getTimeZone("GMT"));
		cal.set(Calendar.YEAR, 2015);
		cal.set(Calendar.MONTH, Calendar.JUNE);
		cal.set(Calendar.DATE, 20);
		cal.set(Calendar.HOUR, 2);
		cal.set(Calendar.MINUTE, 37);
		cal.set(Calendar.SECOND, 14);
		Date expected = cal.getTime();

		assertEquals(expected, DateUtils.parseRfc1123DateTime("Sat, 20 Jun 2015 02:37:14 GMT"));

		assertNull(DateUtils.parseRfc1123DateTime("Sat, 20 Jun 2015 02:37:14"));

		assertNull(DateUtils.parseRfc1123DateTime("Sat, 20 Jun 2015"));
	}

	@Test
	public void testFormatRfc1123DateTime() throws Exception {
		Calendar cal = Calendar.getInstance();
		cal.clear();
		cal.setTimeZone(TimeZone.getTimeZone("GMT+1"));
		cal.set(Calendar.YEAR, 2015);
		cal.set(Calendar.MONTH, Calendar.JUNE);
		cal.set(Calendar.DATE, 20);
		cal.set(Calendar.HOUR, 2);
		cal.set(Calendar.MINUTE, 37);
		cal.set(Calendar.SECOND, 14);
		Date date = cal.getTime();

		TimeZone tz = TimeZone.getTimeZone("GMT");
		assertEquals("Sat, 20 Jun 2015 01:37:14 GMT", DateUtils.formatRfc1123DateTime(date, tz));
	}

	@Test
	public void testParseIso8601DateTime() throws Exception {
		Calendar cal = Calendar.getInstance();
		cal.clear();
		cal.setTimeZone(TimeZone.getTimeZone("GMT"));
		cal.set(Calendar.YEAR, 1997);
		cal.set(Calendar.MONTH, Calendar.JULY);
		cal.set(Calendar.DATE, 16);
		cal.set(Calendar.HOUR, 18);
		cal.set(Calendar.MINUTE, 20);
		cal.set(Calendar.SECOND, 30);
		Date expected = cal.getTime();

		// dates without times or time zones are not supported
		assertNull(DateUtils.parseIso8601DateTime("1997"));
		assertNull(DateUtils.parseIso8601DateTime("1997-07"));
		assertNull(DateUtils.parseIso8601DateTime("1997-07-16"));

		// dates without seconds are not supported
		assertNull(DateUtils.parseIso8601DateTime("1997-07-16T19:20+01:00"));

		// dates with fractional seconds containing less that 3 digits are not supported
		assertNull(DateUtils.parseIso8601DateTime("1997-07-16T19:20:30.45+01:00"));

		assertEquals(expected, DateUtils.parseIso8601DateTime("1997-07-16T19:20:30+01:00"));
		assertEquals(expected, DateUtils.parseIso8601DateTime("1997-07-16T18:20:30Z"));

		cal.set(Calendar.MILLISECOND, 235);
		expected = cal.getTime();

		assertEquals(expected, DateUtils.parseIso8601DateTime("1997-07-16T19:20:30.235+01:00"));
		assertEquals(expected, DateUtils.parseIso8601DateTime("1997-07-16T18:20:30.235Z"));
	}

	@Test
	public void testFormatIso8601DateTime() throws Exception {
		Calendar cal = Calendar.getInstance();
		cal.clear();
		cal.setTimeZone(TimeZone.getTimeZone("GMT+1"));
		cal.set(Calendar.YEAR, 1997);
		cal.set(Calendar.MONTH, Calendar.JULY);
		cal.set(Calendar.DATE, 16);
		cal.set(Calendar.HOUR, 19);
		cal.set(Calendar.MINUTE, 20);
		cal.set(Calendar.SECOND, 30);
		Date date = cal.getTime();

		TimeZone tz = TimeZone.getTimeZone("GMT");
		assertEquals("1997-07-16T18:20:30+00:00", DateUtils.formatIso8601DateTime(date, tz));
	}
}