DateUtil.java

/**
 * Copyright (C) 2013 Johannes Schnatterer
 *
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 * This file is part of nusic.
 *
 * nusic is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * nusic is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with nusic.  If not, see <http://www.gnu.org/licenses/>.
 */
package info.schnatterer.nusic.util;

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

public final class DateUtil {
    public static final int MILLIS_TO_MINUTES = 60000;

    private DateUtil() {
    }

    public static Long toLong(Date date) {
        if (date != null) {
            return date.getTime();
        }
        return null;
    }

    /**
     * Converts a "serialized" date from a {@link Long} object. <b>Note:</b> If
     * the long is implicitly a primitive long, it does not support
     * <code>null</code> values and will therefore always result in 1st January
     * 1970.
     * 
     * You
     * 
     * @param date
     * @return
     */
    public static Date toDate(Long date) {
        if (date != null) {
            return new Date(date);
        }
        return null;
    }

    /**
     * Returns the current date + a number of <code>minutes</code>.
     * 
     * @param minutes
     * @return
     */
    public static Date addMinutes(int minutes) {
        return new Date(System.currentTimeMillis() + minutes
                * MILLIS_TO_MINUTES);
    }

    /**
     * Extracts the date (not the time) from <code>cal</code> and returns the
     * corresponding value for this date and midnight in UTC.<br/>
     * <br/>
     * For example: Input <code>2014-07-22T01:11:11+02:00</code> (UTC+2) equals
     * <code>2014-07-<b>21</b>T23:11:11Z</code> (UTC). But the when passed to
     * the method this returns <code>2014-07-<b>22</b>T00:00:00Z</code>, that is
     * input date at midnight UTC.
     * 
     * @param cal
     * @return
     */
    public static long midnightUtc(Calendar cal) {
        // The "local date"
        int year = cal.get(Calendar.YEAR);
        int month = cal.get(Calendar.MONTH);
        int day = cal.get(Calendar.DAY_OF_MONTH);

        // Switch to UTC
        cal = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
        // Make sure to get EXACTLY midnight (set ms part of the date)
        cal.setTimeInMillis(0);
        // Set the local date for UTC and midnight
        cal.set(year, month, day, 0, 0, 0);
        return cal.getTimeInMillis();
    }

    /**
     * @return the timestamp for tomorrow's date at midnight in UTC.
     * @see #midnightUtc(Calendar)
     */
    public static long tomorrowMidnightUtc() {
        // Get timestamp for tomorrow midnight.
        Calendar cal = Calendar.getInstance();
        cal.add(Calendar.DAY_OF_YEAR, 1);
        return midnightUtc(cal);
    }

    /**
     * @return the timestamp for today's date at midnight in UTC.
     * @see #midnightUtc(Calendar)
     */
    public static long todayMidnightUtc() {
        return midnightUtc(Calendar.getInstance());
    }
}