1 /*
2 * $Id: TimeZoneUtils.java [5/07/2004]
3 *
4 * Copyright (c) 2004, Ben Fortuna
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 *
11 * o Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 *
14 * o Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 *
18 * o Neither the name of Ben Fortuna nor the names of any other contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
23 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
24 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
25 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
26 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
27 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
28 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
29 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
30 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
31 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
32 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
33 */
34 package net.fortuna.ical4j.util;
35
36 import java.util.Calendar;
37 import java.util.Date;
38 import java.util.TimeZone;
39
40 /***
41 * Utility methods relevant to Java timezones.
42 *
43 * @author benfortuna
44 */
45 public final class TimeZoneUtils {
46
47 /***
48 * Constructor made private to enforce static nature.
49 */
50 private TimeZoneUtils() {
51 }
52
53 /***
54 * Determines the first start date of daylight savings for the specified
55 * timezone since January 1, 1970.
56 *
57 * @param timezone
58 * a timezone to determine the start of daylight savings for
59 * @return a date
60 */
61 public static Date getDaylightStart(final TimeZone timezone) {
62 Calendar calendar = Calendar.getInstance(timezone);
63 calendar.setTime(new Date(0));
64
65 // first find the start of standard time..
66 while (timezone.inDaylightTime(calendar.getTime())) {
67 calendar.set(Calendar.DAY_OF_YEAR, calendar
68 .get(Calendar.DAY_OF_YEAR) + 1);
69 }
70
71 // then find the first daylight time after that..
72 while (!timezone.inDaylightTime(calendar.getTime())) {
73 calendar.set(Calendar.DAY_OF_YEAR, calendar
74 .get(Calendar.DAY_OF_YEAR) + 1);
75 }
76
77 return calendar.getTime();
78 }
79
80 /***
81 * Determines the first end date of daylight savings for the specified
82 * timezone since January 1, 1970.
83 *
84 * @param timezone
85 * a timezone to determine the end of daylight savings for
86 * @return a date
87 */
88 public static Date getDaylightEnd(final TimeZone timezone) {
89 Calendar calendar = Calendar.getInstance(timezone);
90 calendar.setTime(new Date(0));
91
92 // first find the start of daylight time..
93 while (!timezone.inDaylightTime(calendar.getTime())) {
94 calendar.set(Calendar.DAY_OF_YEAR, calendar
95 .get(Calendar.DAY_OF_YEAR) + 1);
96 }
97
98 // then find the first standard time after that..
99 while (timezone.inDaylightTime(calendar.getTime())) {
100 calendar.set(Calendar.DAY_OF_YEAR, calendar
101 .get(Calendar.DAY_OF_YEAR) + 1);
102 }
103
104 return calendar.getTime();
105 }
106 }