java/android date time helper

DateTimeHelper.java

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

import android.util.Log;

/**
 * Utility class for parsing and formatting dates and times.
 * 
 * @author Tom Dignan
 */
public final class DateTimeHelper {
	
	private static final SimpleDateFormat DATE_FORMATTER =  
            new SimpleDateFormat("yyyy-MM-dd");

	private static final SimpleDateFormat TIME_FORMATTER =  
            new SimpleDateFormat("hh:mm a");
	
	private static final SimpleDateFormat VERBOSE_LOCALE_DATE_FORMATTER = 
            new SimpleDateFormat("MMM dd',' yyyy");
	
	private static final SimpleDateFormat VERBOSE_LOCALE_TIME_FORMATTER =
		new SimpleDateFormat("hh:mm a z");
	
	private static final SimpleDateFormat VERBOSE_LOCALE_DATE_TIME_FORMATTER =
		new SimpleDateFormat("MMM  dd',' yyyy hh:mm a z");
	
	private static final SimpleDateFormat ISO_8601_FORMATTER = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SS");
	private static final SimpleDateFormat ALMOST_ISO_8601_FORMATTER = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SS");
	
	public static Date parseAlmostISO8601DateTimeWithTSeparator(String datetime) {
		Log.d(TAG, "datetime="+ datetime);
		try {
			return ALMOST_ISO_8601_FORMATTER.parse(datetime);
		} catch (ParseException e) {
			Log.e(TAG, "caught ParseException", e);
			return null;
		}
	}
	
	/**
	 * Parses an ISO8601 formatted datetime and returns a 
	 * java.util.Date object for it, or NULL if parsing
	 * the date fails.
	 * 
	 * @param String datetime
	 * @return Date|null
	 */
	public static Date parseFromISO8601(String datetime) {
		Log.d(TAG, "datetime="+ datetime);
		try {
			return ISO_8601_FORMATTER.parse(datetime);
		} catch (ParseException e) {
			Log.e(TAG, "caught ParseException", e);
			return null;
		}
	}
			
	public static String formatToIS08601(Date date) {
		return ISO_8601_FORMATTER.format(date);
	}

	public static Date parseOnlyDate(String date) {
		Log.d(TAG, "date="+ date);
		try {
			return DATE_FORMATTER.parse(date);
		} catch (ParseException e) {
			Log.e(TAG, "caught ParseException", e);
			return null;
		}
	}
	
	/**
	 * Tries to parse most date times that it is passed, using
	 * some heuristics.
	 * 
	 * @param string
	 * @return
	 */
	public static Date parseDateTime(String datetime) {
		if (datetime.contains("T")) {
			Log.d(TAG, "parseDateTime(): Trying ISO8601 with a T separator");
			return parseAlmostISO8601DateTimeWithTSeparator(datetime);
		} else if (datetime.length() == 10 && datetime.contains("-")) {
			Log.d(TAG, "parseDateTime(): Trying just yyyy-MM-dd date");
			return parseOnlyDate(datetime);
		} else {
			Log.d(TAG, "parseDateTime(): Trying regular ISO8601");
			return parseFromISO8601(datetime);
		}
	}
	
	public static Date parseTime(String time) {
		try {
			return TIME_FORMATTER.parse(time);
		} catch (ParseException e) {
			Log.d(TAG, "parseTime() caught ParseException", e);
			e.printStackTrace();
			return null;
		}
	}

	public static Date parseDate(String date) {
		try {
			return DATE_FORMATTER.parse(date);
		} catch (ParseException e) {
			Log.d(TAG, "parseDate() caught ParseException", e);
			e.printStackTrace();
			return null;
		}
	}
	
	public static Date parseDateAndTime(String strDate, String strTime) {
		Date date = parseDate(strDate);
		Date time = parseTime(strTime);
		long dateMillis = date.getTime();
		long timeMillis = time.getTime();
		return new Date(dateMillis + timeMillis);
	}
	
	public static String pad(int value) {
		if (value < 10) {
			return "0" + value;
		} else {
			return "" + value;
		}
	}

	public static String toLocaleDateTime(Date date) {
		return VERBOSE_LOCALE_DATE_TIME_FORMATTER.format(date);
	}

	public static String toLocaleDate(Date date) {
		return VERBOSE_LOCALE_DATE_FORMATTER.format(date);
	}

	public static String toLocaleTime(Date date) {
		return VERBOSE_LOCALE_TIME_FORMATTER.format(date);
	}
	
	public static Date toLocalTime(Date date) {
		long millisUTC = date.getTime();
		TimeZone tz = TimeZone.getDefault();
		int tzOffset = tz.getOffset(millisUTC);
		if (tz.inDaylightTime(new Date(millisUTC))) {
			millisUTC -= tz.getDSTSavings();
		}
		return new Date(millisUTC + tzOffset);
	}
	
	public static long toLocalTime(long millisUTC) {
		// TODO: Refactor this and save it. Perfect DST code.
		TimeZone tz = TimeZone.getDefault();
		int tzOffset = tz.getOffset(millisUTC);
		if (tz.inDaylightTime(new Date(millisUTC))) {
			millisUTC -= tz.getDSTSavings();
		}
		return millisUTC + tzOffset;
	}
}