Java tutorial
/* * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code 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 * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ /* * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved * (C) Copyright IBM Corp. 1996 - All Rights Reserved * * The original version of this source code and documentation is copyrighted * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These * materials are provided under terms of a License Agreement between Taligent * and Sun. This technology is protected by multiple US and International * patents. This notice and attribution to Taligent may not be removed. * Taligent is a registered trademark of Taligent, Inc. * */ package java.util; import java.io.Serializable; import java.time.ZoneId; import jdk.internal.util.StaticProperty; import sun.security.action.GetPropertyAction; import sun.util.calendar.ZoneInfo; import sun.util.calendar.ZoneInfoFile; import sun.util.locale.provider.TimeZoneNameUtility; /** * <code>TimeZone</code> represents a time zone offset, and also figures out daylight * savings. * * <p> * Typically, you get a <code>TimeZone</code> using <code>getDefault</code> * which creates a <code>TimeZone</code> based on the time zone where the program * is running. For example, for a program running in Japan, <code>getDefault</code> * creates a <code>TimeZone</code> object based on Japanese Standard Time. * * <p> * You can also get a <code>TimeZone</code> using <code>getTimeZone</code> * along with a time zone ID. For instance, the time zone ID for the * U.S. Pacific Time zone is "America/Los_Angeles". So, you can get a * U.S. Pacific Time <code>TimeZone</code> object with: * <blockquote><pre> * TimeZone tz = TimeZone.getTimeZone("America/Los_Angeles"); * </pre></blockquote> * You can use the <code>getAvailableIDs</code> method to iterate through * all the supported time zone IDs. You can then choose a * supported ID to get a <code>TimeZone</code>. * If the time zone you want is not represented by one of the * supported IDs, then a custom time zone ID can be specified to * produce a TimeZone. The syntax of a custom time zone ID is: * * <blockquote><pre> * <a id="CustomID"><i>CustomID:</i></a> * <code>GMT</code> <i>Sign</i> <i>Hours</i> <code>:</code> <i>Minutes</i> * <code>GMT</code> <i>Sign</i> <i>Hours</i> <i>Minutes</i> * <code>GMT</code> <i>Sign</i> <i>Hours</i> * <i>Sign:</i> one of * <code>+ -</code> * <i>Hours:</i> * <i>Digit</i> * <i>Digit</i> <i>Digit</i> * <i>Minutes:</i> * <i>Digit</i> <i>Digit</i> * <i>Digit:</i> one of * <code>0 1 2 3 4 5 6 7 8 9</code> * </pre></blockquote> * * <i>Hours</i> must be between 0 to 23 and <i>Minutes</i> must be * between 00 to 59. For example, "GMT+10" and "GMT+0010" mean ten * hours and ten minutes ahead of GMT, respectively. * <p> * The format is locale independent and digits must be taken from the * Basic Latin block of the Unicode standard. No daylight saving time * transition schedule can be specified with a custom time zone ID. If * the specified string doesn't match the syntax, <code>"GMT"</code> * is used. * <p> * When creating a <code>TimeZone</code>, the specified custom time * zone ID is normalized in the following syntax: * <blockquote><pre> * <a id="NormalizedCustomID"><i>NormalizedCustomID:</i></a> * <code>GMT</code> <i>Sign</i> <i>TwoDigitHours</i> <code>:</code> <i>Minutes</i> * <i>Sign:</i> one of * <code>+ -</code> * <i>TwoDigitHours:</i> * <i>Digit</i> <i>Digit</i> * <i>Minutes:</i> * <i>Digit</i> <i>Digit</i> * <i>Digit:</i> one of * <code>0 1 2 3 4 5 6 7 8 9</code> * </pre></blockquote> * For example, TimeZone.getTimeZone("GMT-8").getID() returns "GMT-08:00". * * <h2>Three-letter time zone IDs</h2> * * For compatibility with JDK 1.1.x, some other three-letter time zone IDs * (such as "PST", "CTT", "AST") are also supported. However, <strong>their * use is deprecated</strong> because the same abbreviation is often used * for multiple time zones (for example, "CST" could be U.S. "Central Standard * Time" and "China Standard Time"), and the Java platform can then only * recognize one of them. * * * @see Calendar * @see GregorianCalendar * @see SimpleTimeZone * @author Mark Davis, David Goldsmith, Chen-Lieh Huang, Alan Liu * @since 1.1 */ public abstract class TimeZone implements Serializable, Cloneable { /** * Sole constructor. (For invocation by subclass constructors, typically * implicit.) */ public TimeZone() { } /** * A style specifier for <code>getDisplayName()</code> indicating * a short name, such as "PST." * @see #LONG * @since 1.2 */ public static final int SHORT = 0; /** * A style specifier for <code>getDisplayName()</code> indicating * a long name, such as "Pacific Standard Time." * @see #SHORT * @since 1.2 */ public static final int LONG = 1; // Constants used internally; unit is milliseconds private static final int ONE_MINUTE = 60 * 1000; private static final int ONE_HOUR = 60 * ONE_MINUTE; private static final int ONE_DAY = 24 * ONE_HOUR; // Proclaim serialization compatibility with JDK 1.1 static final long serialVersionUID = 3581463369166924961L; /** * Gets the time zone offset, for current date, modified in case of * daylight savings. This is the offset to add to UTC to get local time. * <p> * This method returns a historically correct offset if an * underlying <code>TimeZone</code> implementation subclass * supports historical Daylight Saving Time schedule and GMT * offset changes. * * @param era the era of the given date. * @param year the year in the given date. * @param month the month in the given date. * Month is 0-based. e.g., 0 for January. * @param day the day-in-month of the given date. * @param dayOfWeek the day-of-week of the given date. * @param milliseconds the milliseconds in day in <em>standard</em> * local time. * * @return the offset in milliseconds to add to GMT to get local time. * * @see Calendar#ZONE_OFFSET * @see Calendar#DST_OFFSET */ public abstract int getOffset(int era, int year, int month, int day, int dayOfWeek, int milliseconds); /** * Returns the offset of this time zone from UTC at the specified * date. If Daylight Saving Time is in effect at the specified * date, the offset value is adjusted with the amount of daylight * saving. * <p> * This method returns a historically correct offset value if an * underlying TimeZone implementation subclass supports historical * Daylight Saving Time schedule and GMT offset changes. * * @param date the date represented in milliseconds since January 1, 1970 00:00:00 GMT * @return the amount of time in milliseconds to add to UTC to get local time. * * @see Calendar#ZONE_OFFSET * @see Calendar#DST_OFFSET * @since 1.4 */ public int getOffset(long date) { if (inDaylightTime(new Date(date))) { return getRawOffset() + getDSTSavings(); } return getRawOffset(); } /** * Gets the raw GMT offset and the amount of daylight saving of this * time zone at the given time. * @param date the milliseconds (since January 1, 1970, * 00:00:00.000 GMT) at which the time zone offset and daylight * saving amount are found * @param offsets an array of int where the raw GMT offset * (offset[0]) and daylight saving amount (offset[1]) are stored, * or null if those values are not needed. The method assumes that * the length of the given array is two or larger. * @return the total amount of the raw GMT offset and daylight * saving at the specified date. * * @see Calendar#ZONE_OFFSET * @see Calendar#DST_OFFSET */ int getOffsets(long date, int[] offsets) { int rawoffset = getRawOffset(); int dstoffset = 0; if (inDaylightTime(new Date(date))) { dstoffset = getDSTSavings(); } if (offsets != null) { offsets[0] = rawoffset; offsets[1] = dstoffset; } return rawoffset + dstoffset; } /** * Sets the base time zone offset to GMT. * This is the offset to add to UTC to get local time. * <p> * If an underlying <code>TimeZone</code> implementation subclass * supports historical GMT offset changes, the specified GMT * offset is set as the latest GMT offset and the difference from * the known latest GMT offset value is used to adjust all * historical GMT offset values. * * @param offsetMillis the given base time zone offset to GMT. */ public abstract void setRawOffset(int offsetMillis); /** * Returns the amount of time in milliseconds to add to UTC to get * standard time in this time zone. Because this value is not * affected by daylight saving time, it is called <I>raw * offset</I>. * <p> * If an underlying <code>TimeZone</code> implementation subclass * supports historical GMT offset changes, the method returns the * raw offset value of the current date. In Honolulu, for example, * its raw offset changed from GMT-10:30 to GMT-10:00 in 1947, and * this method always returns -36000000 milliseconds (i.e., -10 * hours). * * @return the amount of raw offset time in milliseconds to add to UTC. * @see Calendar#ZONE_OFFSET */ public abstract int getRawOffset(); /** * Gets the ID of this time zone. * @return the ID of this time zone. */ public String getID() { return ID; } /** * Sets the time zone ID. This does not change any other data in * the time zone object. * @param ID the new time zone ID. */ public void setID(String ID) { if (ID == null) { throw new NullPointerException(); } this.ID = ID; this.zoneId = null; // invalidate cache } /** * Returns a long standard time name of this {@code TimeZone} suitable for * presentation to the user in the default locale. * * <p>This method is equivalent to: * <blockquote><pre> * getDisplayName(false, {@link #LONG}, * Locale.getDefault({@link Locale.Category#DISPLAY})) * </pre></blockquote> * * @return the human-readable name of this time zone in the default locale. * @since 1.2 * @see #getDisplayName(boolean, int, Locale) * @see Locale#getDefault(Locale.Category) * @see Locale.Category */ public final String getDisplayName() { return getDisplayName(false, LONG, Locale.getDefault(Locale.Category.DISPLAY)); } /** * Returns a long standard time name of this {@code TimeZone} suitable for * presentation to the user in the specified {@code locale}. * * <p>This method is equivalent to: * <blockquote><pre> * getDisplayName(false, {@link #LONG}, locale) * </pre></blockquote> * * @param locale the locale in which to supply the display name. * @return the human-readable name of this time zone in the given locale. * @exception NullPointerException if {@code locale} is {@code null}. * @since 1.2 * @see #getDisplayName(boolean, int, Locale) */ public final String getDisplayName(Locale locale) { return getDisplayName(false, LONG, locale); } /** * Returns a name in the specified {@code style} of this {@code TimeZone} * suitable for presentation to the user in the default locale. If the * specified {@code daylight} is {@code true}, a Daylight Saving Time name * is returned (even if this {@code TimeZone} doesn't observe Daylight Saving * Time). Otherwise, a Standard Time name is returned. * * <p>This method is equivalent to: * <blockquote><pre> * getDisplayName(daylight, style, * Locale.getDefault({@link Locale.Category#DISPLAY})) * </pre></blockquote> * * @param daylight {@code true} specifying a Daylight Saving Time name, or * {@code false} specifying a Standard Time name * @param style either {@link #LONG} or {@link #SHORT} * @return the human-readable name of this time zone in the default locale. * @exception IllegalArgumentException if {@code style} is invalid. * @since 1.2 * @see #getDisplayName(boolean, int, Locale) * @see Locale#getDefault(Locale.Category) * @see Locale.Category * @see java.text.DateFormatSymbols#getZoneStrings() */ public final String getDisplayName(boolean daylight, int style) { return getDisplayName(daylight, style, Locale.getDefault(Locale.Category.DISPLAY)); } /** * Returns a name in the specified {@code style} of this {@code TimeZone} * suitable for presentation to the user in the specified {@code * locale}. If the specified {@code daylight} is {@code true}, a Daylight * Saving Time name is returned (even if this {@code TimeZone} doesn't * observe Daylight Saving Time). Otherwise, a Standard Time name is * returned. * * <p>When looking up a time zone name, the {@linkplain * ResourceBundle.Control#getCandidateLocales(String,Locale) default * <code>Locale</code> search path of <code>ResourceBundle</code>} derived * from the specified {@code locale} is used. (No {@linkplain * ResourceBundle.Control#getFallbackLocale(String,Locale) fallback * <code>Locale</code>} search is performed.) If a time zone name in any * {@code Locale} of the search path, including {@link Locale#ROOT}, is * found, the name is returned. Otherwise, a string in the * <a href="#NormalizedCustomID">normalized custom ID format</a> is returned. * * @param daylight {@code true} specifying a Daylight Saving Time name, or * {@code false} specifying a Standard Time name * @param style either {@link #LONG} or {@link #SHORT} * @param locale the locale in which to supply the display name. * @return the human-readable name of this time zone in the given locale. * @exception IllegalArgumentException if {@code style} is invalid. * @exception NullPointerException if {@code locale} is {@code null}. * @since 1.2 * @see java.text.DateFormatSymbols#getZoneStrings() */ public String getDisplayName(boolean daylight, int style, Locale locale) { if (style != SHORT && style != LONG) { throw new IllegalArgumentException("Illegal style: " + style); } String id = getID(); String name = TimeZoneNameUtility.retrieveDisplayName(id, daylight, style, locale); if (name != null) { return name; } if (id.startsWith("GMT") && id.length() > 3) { char sign = id.charAt(3); if (sign == '+' || sign == '-') { return id; } } int offset = getRawOffset(); if (daylight) { offset += getDSTSavings(); } return ZoneInfoFile.toCustomID(offset); } private static String[] getDisplayNames(String id, Locale locale) { return TimeZoneNameUtility.retrieveDisplayNames(id, locale); } /** * Returns the amount of time to be added to local standard time * to get local wall clock time. * * <p>The default implementation returns 3600000 milliseconds * (i.e., one hour) if a call to {@link #useDaylightTime()} * returns {@code true}. Otherwise, 0 (zero) is returned. * * <p>If an underlying {@code TimeZone} implementation subclass * supports historical and future Daylight Saving Time schedule * changes, this method returns the amount of saving time of the * last known Daylight Saving Time rule that can be a future * prediction. * * <p>If the amount of saving time at any given time stamp is * required, construct a {@link Calendar} with this {@code * TimeZone} and the time stamp, and call {@link Calendar#get(int) * Calendar.get}{@code (}{@link Calendar#DST_OFFSET}{@code )}. * * @return the amount of saving time in milliseconds * @since 1.4 * @see #inDaylightTime(Date) * @see #getOffset(long) * @see #getOffset(int,int,int,int,int,int) * @see Calendar#ZONE_OFFSET */ public int getDSTSavings() { if (useDaylightTime()) { return 3600000; } return 0; } /** * Queries if this {@code TimeZone} uses Daylight Saving Time. * * <p>If an underlying {@code TimeZone} implementation subclass * supports historical and future Daylight Saving Time schedule * changes, this method refers to the last known Daylight Saving Time * rule that can be a future prediction and may not be the same as * the current rule. Consider calling {@link #observesDaylightTime()} * if the current rule should also be taken into account. * * @return {@code true} if this {@code TimeZone} uses Daylight Saving Time, * {@code false}, otherwise. * @see #inDaylightTime(Date) * @see Calendar#DST_OFFSET */ public abstract boolean useDaylightTime(); /** * Returns {@code true} if this {@code TimeZone} is currently in * Daylight Saving Time, or if a transition from Standard Time to * Daylight Saving Time occurs at any future time. * * <p>The default implementation returns {@code true} if * {@code useDaylightTime()} or {@code inDaylightTime(new Date())} * returns {@code true}. * * @return {@code true} if this {@code TimeZone} is currently in * Daylight Saving Time, or if a transition from Standard Time to * Daylight Saving Time occurs at any future time; {@code false} * otherwise. * @since 1.7 * @see #useDaylightTime() * @see #inDaylightTime(Date) * @see Calendar#DST_OFFSET */ public boolean observesDaylightTime() { return useDaylightTime() || inDaylightTime(new Date()); } /** * Queries if the given {@code date} is in Daylight Saving Time in * this time zone. * * @param date the given Date. * @return {@code true} if the given date is in Daylight Saving Time, * {@code false}, otherwise. */ public abstract boolean inDaylightTime(Date date); /** * Gets the <code>TimeZone</code> for the given ID. * * @param ID the ID for a <code>TimeZone</code>, either an abbreviation * such as "PST", a full name such as "America/Los_Angeles", or a custom * ID such as "GMT-8:00". Note that the support of abbreviations is * for JDK 1.1.x compatibility only and full names should be used. * * @return the specified <code>TimeZone</code>, or the GMT zone if the given ID * cannot be understood. */ public static synchronized TimeZone getTimeZone(String ID) { return getTimeZone(ID, true); } /** * Gets the {@code TimeZone} for the given {@code zoneId}. * * @param zoneId a {@link ZoneId} from which the time zone ID is obtained * @return the specified {@code TimeZone}, or the GMT zone if the given ID * cannot be understood. * @throws NullPointerException if {@code zoneId} is {@code null} * @since 1.8 */ public static TimeZone getTimeZone(ZoneId zoneId) { String tzid = zoneId.getId(); // throws an NPE if null char c = tzid.charAt(0); if (c == '+' || c == '-') { tzid = "GMT" + tzid; } else if (c == 'Z' && tzid.length() == 1) { tzid = "UTC"; } return getTimeZone(tzid, true); } /** * Converts this {@code TimeZone} object to a {@code ZoneId}. * * @return a {@code ZoneId} representing the same time zone as this * {@code TimeZone} * @since 1.8 */ public ZoneId toZoneId() { ZoneId zId = zoneId; if (zId == null) { zoneId = zId = toZoneId0(); } return zId; } private ZoneId toZoneId0() { String id = getID(); TimeZone defaultZone = defaultTimeZone; // are we not defaultTimeZone but our id is equal to default's? if (defaultZone != this && defaultZone != null && id.equals(defaultZone.getID())) { // delegate to default TZ which is effectively immutable return defaultZone.toZoneId(); } // derive it ourselves if (ZoneInfoFile.useOldMapping() && id.length() == 3) { if ("EST".equals(id)) return ZoneId.of("America/New_York"); if ("MST".equals(id)) return ZoneId.of("America/Denver"); if ("HST".equals(id)) return ZoneId.of("America/Honolulu"); } return ZoneId.of(id, ZoneId.SHORT_IDS); } private static TimeZone getTimeZone(String ID, boolean fallback) { TimeZone tz = ZoneInfo.getTimeZone(ID); if (tz == null) { tz = parseCustomTimeZone(ID); if (tz == null && fallback) { tz = new ZoneInfo(GMT_ID, 0); } } return tz; } /** * Gets the available IDs according to the given time zone offset in milliseconds. * * @param rawOffset the given time zone GMT offset in milliseconds. * @return an array of IDs, where the time zone for that ID has * the specified GMT offset. For example, "America/Phoenix" and "America/Denver" * both have GMT-07:00, but differ in daylight saving behavior. * @see #getRawOffset() */ public static synchronized String[] getAvailableIDs(int rawOffset) { return ZoneInfo.getAvailableIDs(rawOffset); } /** * Gets all the available IDs supported. * @return an array of IDs. */ public static synchronized String[] getAvailableIDs() { return ZoneInfo.getAvailableIDs(); } /** * Gets the platform defined TimeZone ID. **/ private static native String getSystemTimeZoneID(String javaHome); /** * Gets the custom time zone ID based on the GMT offset of the * platform. (e.g., "GMT+08:00") */ private static native String getSystemGMTOffsetID(); /** * Gets the default {@code TimeZone} of the Java virtual machine. If the * cached default {@code TimeZone} is available, its clone is returned. * Otherwise, the method takes the following steps to determine the default * time zone. * * <ul> * <li>Use the {@code user.timezone} property value as the default * time zone ID if it's available.</li> * <li>Detect the platform time zone ID. The source of the * platform time zone and ID mapping may vary with implementation.</li> * <li>Use {@code GMT} as the last resort if the given or detected * time zone ID is unknown.</li> * </ul> * * <p>The default {@code TimeZone} created from the ID is cached, * and its clone is returned. The {@code user.timezone} property * value is set to the ID upon return. * * @return the default {@code TimeZone} * @see #setDefault(TimeZone) */ public static TimeZone getDefault() { return (TimeZone) getDefaultRef().clone(); } /** * Returns the reference to the default TimeZone object. This * method doesn't create a clone. */ static TimeZone getDefaultRef() { TimeZone defaultZone = defaultTimeZone; if (defaultZone == null) { // Need to initialize the default time zone. defaultZone = setDefaultZone(); assert defaultZone != null; } // Don't clone here. return defaultZone; } private static synchronized TimeZone setDefaultZone() { TimeZone tz; // get the time zone ID from the system properties Properties props = GetPropertyAction.privilegedGetProperties(); String zoneID = props.getProperty("user.timezone"); // if the time zone ID is not set (yet), perform the // platform to Java time zone ID mapping. if (zoneID == null || zoneID.isEmpty()) { String javaHome = StaticProperty.javaHome(); try { zoneID = getSystemTimeZoneID(javaHome); if (zoneID == null) { zoneID = GMT_ID; } } catch (NullPointerException e) { zoneID = GMT_ID; } } // Get the time zone for zoneID. But not fall back to // "GMT" here. tz = getTimeZone(zoneID, false); if (tz == null) { // If the given zone ID is unknown in Java, try to // get the GMT-offset-based time zone ID, // a.k.a. custom time zone ID (e.g., "GMT-08:00"). String gmtOffsetID = getSystemGMTOffsetID(); if (gmtOffsetID != null) { zoneID = gmtOffsetID; } tz = getTimeZone(zoneID, true); } assert tz != null; final String id = zoneID; props.setProperty("user.timezone", id); defaultTimeZone = tz; return tz; } /** * Sets the {@code TimeZone} that is returned by the {@code getDefault} * method. {@code zone} is cached. If {@code zone} is null, the cached * default {@code TimeZone} is cleared. This method doesn't change the value * of the {@code user.timezone} property. * * @param zone the new default {@code TimeZone}, or null * @throws SecurityException if the security manager's {@code checkPermission} * denies {@code PropertyPermission("user.timezone", * "write")} * @see #getDefault * @see PropertyPermission */ public static void setDefault(TimeZone zone) { SecurityManager sm = System.getSecurityManager(); if (sm != null) { sm.checkPermission(new PropertyPermission("user.timezone", "write")); } // by saving a defensive clone and returning a clone in getDefault() too, // the defaultTimeZone instance is isolated from user code which makes it // effectively immutable. This is important to avoid races when the // following is evaluated in ZoneId.systemDefault(): // TimeZone.getDefault().toZoneId(). defaultTimeZone = (zone == null) ? null : (TimeZone) zone.clone(); } /** * Returns true if this zone has the same rule and offset as another zone. * That is, if this zone differs only in ID, if at all. Returns false * if the other zone is null. * @param other the <code>TimeZone</code> object to be compared with * @return true if the other zone is not null and is the same as this one, * with the possible exception of the ID * @since 1.2 */ public boolean hasSameRules(TimeZone other) { return other != null && getRawOffset() == other.getRawOffset() && useDaylightTime() == other.useDaylightTime(); } /** * Creates a copy of this <code>TimeZone</code>. * * @return a clone of this <code>TimeZone</code> */ public Object clone() { try { return super.clone(); } catch (CloneNotSupportedException e) { throw new InternalError(e); } } /** * The null constant as a TimeZone. */ static final TimeZone NO_TIMEZONE = null; // =======================privates=============================== /** * The string identifier of this <code>TimeZone</code>. This is a * programmatic identifier used internally to look up <code>TimeZone</code> * objects from the system table and also to map them to their localized * display names. <code>ID</code> values are unique in the system * table but may not be for dynamically created zones. * @serial */ private String ID; /** * Cached {@link ZoneId} for this TimeZone */ private transient ZoneId zoneId; private static volatile TimeZone defaultTimeZone; static final String GMT_ID = "GMT"; private static final int GMT_ID_LENGTH = 3; /** * Parses a custom time zone identifier and returns a corresponding zone. * This method doesn't support the RFC 822 time zone format. (e.g., +hhmm) * * @param id a string of the <a href="#CustomID">custom ID form</a>. * @return a newly created TimeZone with the given offset and * no daylight saving time, or null if the id cannot be parsed. */ private static final TimeZone parseCustomTimeZone(String id) { int length; // Error if the length of id isn't long enough or id doesn't // start with "GMT". if ((length = id.length()) < (GMT_ID_LENGTH + 2) || id.indexOf(GMT_ID) != 0) { return null; } ZoneInfo zi; // First, we try to find it in the cache with the given // id. Even the id is not normalized, the returned ZoneInfo // should have its normalized id. zi = ZoneInfoFile.getZoneInfo(id); if (zi != null) { return zi; } int index = GMT_ID_LENGTH; boolean negative = false; char c = id.charAt(index++); if (c == '-') { negative = true; } else if (c != '+') { return null; } int hours = 0; int num = 0; int countDelim = 0; int len = 0; while (index < length) { c = id.charAt(index++); if (c == ':') { if (countDelim > 0) { return null; } if (len > 2) { return null; } hours = num; countDelim++; num = 0; len = 0; continue; } if (c < '0' || c > '9') { return null; } num = num * 10 + (c - '0'); len++; } if (index != length) { return null; } if (countDelim == 0) { if (len <= 2) { hours = num; num = 0; } else { hours = num / 100; num %= 100; } } else { if (len != 2) { return null; } } if (hours > 23 || num > 59) { return null; } int gmtOffset = (hours * 60 + num) * 60 * 1000; if (gmtOffset == 0) { zi = ZoneInfoFile.getZoneInfo(GMT_ID); if (negative) { zi.setID("GMT-00:00"); } else { zi.setID("GMT+00:00"); } } else { zi = ZoneInfoFile.getCustomTimeZone(id, negative ? -gmtOffset : gmtOffset); } return zi; } }