* The rules model all the historic and future transitions for a time-zone. * {@link ZoneOffsetTransition} is used for known transitions, typically historic. * {@link ZoneOffsetTransitionRule} is used for future transitions that are based * on the result of an algorithm. *

* The rules are loaded via {@link ZoneRulesProvider} using a {@link ZoneId}. * The same rules may be shared internally between multiple zone IDs. *

* Serializing an instance of {@code ZoneRules} will store the entire set of rules. * It does not store the zone ID as it is not part of the state of this object. *

* A rule implementation may or may not store full information about historic * and future transitions, and the information stored is only as accurate as * that supplied to the implementation by the rules provider. * Applications should treat the data provided as representing the best information * available to the implementation of this rule. * * @implSpec * This class is immutable and thread-safe. * * @since 1.8 */ public final class ZoneRules implements Serializable { /** * Serialization version. */ private static final long serialVersionUID = 3044319355680032515L; /** * The last year to have its transitions cached. */ private static final int LAST_CACHED_YEAR = 2100; /** * The transitions between standard offsets (epoch seconds), sorted. */ private final long[] standardTransitions; /** * The standard offsets. */ private final ZoneOffset[] standardOffsets; /** * The transitions between instants (epoch seconds), sorted. */ private final long[] savingsInstantTransitions; /** * The transitions between local date-times, sorted. * This is a paired array, where the first entry is the start of the transition * and the second entry is the end of the transition. */ private final LocalDateTime[] savingsLocalTransitions; /** * The wall offsets. */ private final ZoneOffset[] wallOffsets; /** * The last rule. */ private final ZoneOffsetTransitionRule[] lastRules; /** * The map of recent transitions. */ private final transient ConcurrentMap lastRulesCache = new ConcurrentHashMap(); /** * The zero-length long array. */ private static final long[] EMPTY_LONG_ARRAY = new long[0]; /** * The zero-length lastrules array. */ private static final ZoneOffsetTransitionRule[] EMPTY_LASTRULES = new ZoneOffsetTransitionRule[0]; /** * The zero-length ldt array. */ private static final LocalDateTime[] EMPTY_LDT_ARRAY = new LocalDateTime[0]; /** * Obtains an instance of a ZoneRules. * * @param baseStandardOffset the standard offset to use before legal rules were set, not null * @param baseWallOffset the wall offset to use before legal rules were set, not null * @param standardOffsetTransitionList the list of changes to the standard offset, not null * @param transitionList the list of transitions, not null * @param lastRules the recurring last rules, size 16 or less, not null * @return the zone rules, not null */ public static ZoneRules of(ZoneOffset baseStandardOffset, ZoneOffset baseWallOffset, List standardOffsetTransitionList, List transitionList, List lastRules) { Objects.requireNonNull(baseStandardOffset, "baseStandardOffset"); Objects.requireNonNull(baseWallOffset, "baseWallOffset"); Objects.requireNonNull(standardOffsetTransitionList, "standardOffsetTransitionList"); Objects.requireNonNull(transitionList, "transitionList"); Objects.requireNonNull(lastRules, "lastRules"); return new ZoneRules(baseStandardOffset, baseWallOffset, standardOffsetTransitionList, transitionList, lastRules); } /** * Obtains an instance of ZoneRules that has fixed zone rules. * * @param offset the offset this fixed zone rules is based on, not null * @return the zone rules, not null * @see #isFixedOffset() */ public static ZoneRules of(ZoneOffset offset) { Objects.requireNonNull(offset, "offset"); return new ZoneRules(offset); } /** * Creates an instance. * * @param baseStandardOffset the standard offset to use before legal rules were set, not null * @param baseWallOffset the wall offset to use before legal rules were set, not null * @param standardOffsetTransitionList the list of changes to the standard offset, not null * @param transitionList the list of transitions, not null * @param lastRules the recurring last rules, size 16 or less, not null */ ZoneRules(ZoneOffset baseStandardOffset, ZoneOffset baseWallOffset, List standardOffsetTransitionList, List transitionList, List lastRules) { super(); // convert standard transitions this.standardTransitions = new long[standardOffsetTransitionList.size()]; this.standardOffsets = new ZoneOffset[standardOffsetTransitionList.size() + 1]; this.standardOffsets[0] = baseStandardOffset; for (int i = 0; i < standardOffsetTransitionList.size(); i++) { this.standardTransitions[i] = standardOffsetTransitionList.get(i).toEpochSecond(); this.standardOffsets[i + 1] = standardOffsetTransitionList.get(i).getOffsetAfter(); } // convert savings transitions to locals List localTransitionList = new ArrayList<>(); List localTransitionOffsetList = new ArrayList<>(); localTransitionOffsetList.add(baseWallOffset); for (ZoneOffsetTransition trans : transitionList) { if (trans.isGap()) { localTransitionList.add(trans.getDateTimeBefore()); localTransitionList.add(trans.getDateTimeAfter()); } else { localTransitionList.add(trans.getDateTimeAfter()); localTransitionList.add(trans.getDateTimeBefore()); } localTransitionOffsetList.add(trans.getOffsetAfter()); } this.savingsLocalTransitions = localTransitionList.toArray(new LocalDateTime[localTransitionList.size()]); this.wallOffsets = localTransitionOffsetList.toArray(new ZoneOffset[localTransitionOffsetList.size()]); // convert savings transitions to instants this.savingsInstantTransitions = new long[transitionList.size()]; for (int i = 0; i < transitionList.size(); i++) { this.savingsInstantTransitions[i] = transitionList.get(i).toEpochSecond(); } // last rules if (lastRules.size() > 16) { throw new IllegalArgumentException("Too many transition rules"); } this.lastRules = lastRules.toArray(new ZoneOffsetTransitionRule[lastRules.size()]); } /** * Constructor. * * @param standardTransitions the standard transitions, not null * @param standardOffsets the standard offsets, not null * @param savingsInstantTransitions the standard transitions, not null * @param wallOffsets the wall offsets, not null * @param lastRules the recurring last rules, size 15 or less, not null */ private ZoneRules(long[] standardTransitions, ZoneOffset[] standardOffsets, long[] savingsInstantTransitions, ZoneOffset[] wallOffsets, ZoneOffsetTransitionRule[] lastRules) { super(); this.standardTransitions = standardTransitions; this.standardOffsets = standardOffsets; this.savingsInstantTransitions = savingsInstantTransitions; this.wallOffsets = wallOffsets; this.lastRules = lastRules; if (savingsInstantTransitions.length == 0) { this.savingsLocalTransitions = EMPTY_LDT_ARRAY; } else { // convert savings transitions to locals List localTransitionList = new ArrayList<>(); for (int i = 0; i < savingsInstantTransitions.length; i++) { ZoneOffset before = wallOffsets[i]; ZoneOffset after = wallOffsets[i + 1]; ZoneOffsetTransition trans = new ZoneOffsetTransition(savingsInstantTransitions[i], before, after); if (trans.isGap()) { localTransitionList.add(trans.getDateTimeBefore()); localTransitionList.add(trans.getDateTimeAfter()); } else { localTransitionList.add(trans.getDateTimeAfter()); localTransitionList.add(trans.getDateTimeBefore()); } } this.savingsLocalTransitions = localTransitionList.toArray(new LocalDateTime[localTransitionList.size()]); } } /** * Creates an instance of ZoneRules that has fixed zone rules. * * @param offset the offset this fixed zone rules is based on, not null * @return the zone rules, not null * @see #isFixedOffset() */ private ZoneRules(ZoneOffset offset) { this.standardOffsets = new ZoneOffset[1]; this.standardOffsets[0] = offset; this.standardTransitions = EMPTY_LONG_ARRAY; this.savingsInstantTransitions = EMPTY_LONG_ARRAY; this.savingsLocalTransitions = EMPTY_LDT_ARRAY; this.wallOffsets = standardOffsets; this.lastRules = EMPTY_LASTRULES; } /** * Defend against malicious streams. * * @throws InvalidObjectException always */ private void readObject(ObjectInputStream s) throws InvalidObjectException { throw new InvalidObjectException("Deserialization via serialization delegate"); } /** * Writes the object using a * dedicated serialized form. * @serialData *

{@code
     *
     *   out.writeByte(1);  // identifies a ZoneRules
     *   out.writeInt(standardTransitions.length);
     *   for (long trans : standardTransitions) {
     *       Ser.writeEpochSec(trans, out);
     *   }
     *   for (ZoneOffset offset : standardOffsets) {
     *       Ser.writeOffset(offset, out);
     *   }
     *   out.writeInt(savingsInstantTransitions.length);
     *   for (long trans : savingsInstantTransitions) {
     *       Ser.writeEpochSec(trans, out);
     *   }
     *   for (ZoneOffset offset : wallOffsets) {
     *       Ser.writeOffset(offset, out);
     *   }
     *   out.writeByte(lastRules.length);
     *   for (ZoneOffsetTransitionRule rule : lastRules) {
     *       rule.writeExternal(out);
     *   }
     * }
     * 

* Epoch second values used for offsets are encoded in a variable * length form to make the common cases put fewer bytes in the stream. *

{@code
     *
     *  static void writeEpochSec(long epochSec, DataOutput out) throws IOException {
     *     if (epochSec >= -4575744000L && epochSec < 10413792000L && epochSec % 900 == 0) {  // quarter hours between 1825 and 2300
     *         int store = (int) ((epochSec + 4575744000L) / 900);
     *         out.writeByte((store >>> 16) & 255);
     *         out.writeByte((store >>> 8) & 255);
     *         out.writeByte(store & 255);
     *      } else {
     *          out.writeByte(255);
     *          out.writeLong(epochSec);
     *      }
     *  }
     * }
     * 

* ZoneOffset values are encoded in a variable length form so the * common cases put fewer bytes in the stream. *

{@code
     *
     *  static void writeOffset(ZoneOffset offset, DataOutput out) throws IOException {
     *     final int offsetSecs = offset.getTotalSeconds();
     *     int offsetByte = offsetSecs % 900 == 0 ? offsetSecs / 900 : 127;  // compress to -72 to +72
     *     out.writeByte(offsetByte);
     *     if (offsetByte == 127) {
     *         out.writeInt(offsetSecs);
     *     }
     * }
     *}
     * 

* The mapping from an instant to an offset is simple, there is only * one valid offset for each instant. * This method returns that offset. * * @param instant the instant to find the offset for, not null, but null * may be ignored if the rules have a single offset for all instants * @return the offset, not null */ public ZoneOffset getOffset(Instant instant) { if (savingsInstantTransitions.length == 0) { return standardOffsets[0]; } long epochSec = instant.getEpochSecond(); // check if using last rules if (lastRules.length > 0 && epochSec > savingsInstantTransitions[savingsInstantTransitions.length - 1]) { int year = findYear(epochSec, wallOffsets[wallOffsets.length - 1]); ZoneOffsetTransition[] transArray = findTransitionArray(year); ZoneOffsetTransition trans = null; for (int i = 0; i < transArray.length; i++) { trans = transArray[i]; if (epochSec < trans.toEpochSecond()) { return trans.getOffsetBefore(); } } return trans.getOffsetAfter(); } // using historic rules int index = Arrays.binarySearch(savingsInstantTransitions, epochSec); if (index < 0) { // switch negative insert position to start of matched range index = -index - 2; } return wallOffsets[index + 1]; } /** * Gets a suitable offset for the specified local date-time in these rules. *

* The mapping from a local date-time to an offset is not straightforward. * There are three cases: *

*
• Normal, with one valid offset. For the vast majority of the year, the normal * case applies, where there is a single valid offset for the local date-time.
*
• Gap, with zero valid offsets. This is when clocks jump forward typically * due to the spring daylight savings change from "winter" to "summer". * In a gap there are local date-time values with no valid offset.
*
• Overlap, with two valid offsets. This is when clocks are set back typically * due to the autumn daylight savings change from "summer" to "winter". * In an overlap there are local date-time values with two valid offsets.
*

* Since, in the case of Gap and Overlap, the offset returned is a "best" value, rather * than the "correct" value, it should be treated with care. Applications that care * about the correct offset should use a combination of this method, * {@link #getValidOffsets(LocalDateTime)} and {@link #getTransition(LocalDateTime)}. * * @param localDateTime the local date-time to query, not null, but null * may be ignored if the rules have a single offset for all instants * @return the best available offset for the local date-time, not null */ public ZoneOffset getOffset(LocalDateTime localDateTime) { Object info = getOffsetInfo(localDateTime); if (info instanceof ZoneOffsetTransition) { return ((ZoneOffsetTransition) info).getOffsetBefore(); } return (ZoneOffset) info; } /** * Gets the offset applicable at the specified local date-time in these rules. *

* The mapping from a local date-time to an offset is not straightforward. * There are three cases: *

*
• Normal, with one valid offset. For the vast majority of the year, the normal * case applies, where there is a single valid offset for the local date-time.
*
• Gap, with zero valid offsets. This is when clocks jump forward typically * due to the spring daylight savings change from "winter" to "summer". * In a gap there are local date-time values with no valid offset.
*
• Overlap, with two valid offsets. This is when clocks are set back typically * due to the autumn daylight savings change from "summer" to "winter". * In an overlap there are local date-time values with two valid offsets.
*

* There are various ways to handle the conversion from a {@code LocalDateTime}. * One technique, using this method, would be: *

     *  List<ZoneOffset> validOffsets = rules.getOffset(localDT);
     *  if (validOffsets.size() == 1) {
     *    // Normal case: only one valid offset
     *    zoneOffset = validOffsets.get(0);
     *  } else {
     *    // Gap or Overlap: determine what to do from transition (which will be non-null)
     *    ZoneOffsetTransition trans = rules.getTransition(localDT);
     *  }
     * 

* In theory, it is possible for there to be more than two valid offsets. * This would happen if clocks to be put back more than once in quick succession. * This has never happened in the history of time-zones and thus has no special handling. * However, if it were to happen, then the list would return more than 2 entries. * * @param localDateTime the local date-time to query for valid offsets, not null, but null * may be ignored if the rules have a single offset for all instants * @return the list of valid offsets, may be immutable, not null */ public List getValidOffsets(LocalDateTime localDateTime) { // should probably be optimized Object info = getOffsetInfo(localDateTime); if (info instanceof ZoneOffsetTransition) { return ((ZoneOffsetTransition) info).getValidOffsets(); } return Collections.singletonList((ZoneOffset) info); } /** * Gets the offset transition applicable at the specified local date-time in these rules. *

* The mapping from a local date-time to an offset is not straightforward. * There are three cases: *

*
• Normal, with one valid offset. For the vast majority of the year, the normal * case applies, where there is a single valid offset for the local date-time.
*
• Gap, with zero valid offsets. This is when clocks jump forward typically * due to the spring daylight savings change from "winter" to "summer". * In a gap there are local date-time values with no valid offset.
*
• Overlap, with two valid offsets. This is when clocks are set back typically * due to the autumn daylight savings change from "summer" to "winter". * In an overlap there are local date-time values with two valid offsets.
*

* There are various ways to handle the conversion from a {@code LocalDateTime}. * One technique, using this method, would be: *

     *  ZoneOffsetTransition trans = rules.getTransition(localDT);
     *  if (trans == null) {
     *    // Gap or Overlap: determine what to do from transition
     *  } else {
     *    // Normal case: only one valid offset
     *    zoneOffset = rule.getOffset(localDT);
     *  }
     * 

* This provides access to historic information on how the standard offset * has changed over time. * The standard offset is the offset before any daylight saving time is applied. * This is typically the offset applicable during winter. * * @param instant the instant to find the offset information for, not null, but null * may be ignored if the rules have a single offset for all instants * @return the standard offset, not null */ public ZoneOffset getStandardOffset(Instant instant) { if (savingsInstantTransitions.length == 0) { return standardOffsets[0]; } long epochSec = instant.getEpochSecond(); int index = Arrays.binarySearch(standardTransitions, epochSec); if (index < 0) { // switch negative insert position to start of matched range index = -index - 2; } return standardOffsets[index + 1]; } /** * Gets the amount of daylight savings in use for the specified instant in this zone. *

* This provides access to historic information on how the amount of daylight * savings has changed over time. * This is the difference between the standard offset and the actual offset. * Typically the amount is zero during winter and one hour during summer. * Time-zones are second-based, so the nanosecond part of the duration will be zero. *

* This default implementation calculates the duration from the * {@link #getOffset(java.time.Instant) actual} and * {@link #getStandardOffset(java.time.Instant) standard} offsets. * * @param instant the instant to find the daylight savings for, not null, but null * may be ignored if the rules have a single offset for all instants * @return the difference between the standard and actual offset, not null */ public Duration getDaylightSavings(Instant instant) { if (savingsInstantTransitions.length == 0) { return Duration.ZERO; } ZoneOffset standardOffset = getStandardOffset(instant); ZoneOffset actualOffset = getOffset(instant); return Duration.ofSeconds(actualOffset.getTotalSeconds() - standardOffset.getTotalSeconds()); } /** * Checks if the specified instant is in daylight savings. *

* This checks if the standard offset and the actual offset are the same * for the specified instant. * If they are not, it is assumed that daylight savings is in operation. *

* This default implementation compares the {@link #getOffset(java.time.Instant) actual} * and {@link #getStandardOffset(java.time.Instant) standard} offsets. * * @param instant the instant to find the offset information for, not null, but null * may be ignored if the rules have a single offset for all instants * @return the standard offset, not null */ public boolean isDaylightSavings(Instant instant) { return (getStandardOffset(instant).equals(getOffset(instant)) == false); } /** * Checks if the offset date-time is valid for these rules. *

* To be valid, the local date-time must not be in a gap and the offset * must match one of the valid offsets. *

* This default implementation checks if {@link #getValidOffsets(java.time.LocalDateTime)} * contains the specified offset. * * @param localDateTime the date-time to check, not null, but null * may be ignored if the rules have a single offset for all instants * @param offset the offset to check, null returns false * @return true if the offset date-time is valid for these rules */ public boolean isValidOffset(LocalDateTime localDateTime, ZoneOffset offset) { return getValidOffsets(localDateTime).contains(offset); } /** * Gets the next transition after the specified instant. *

* This returns details of the next transition after the specified instant. * For example, if the instant represents a point where "Summer" daylight savings time * applies, then the method will return the transition to the next "Winter" time. * * @param instant the instant to get the next transition after, not null, but null * may be ignored if the rules have a single offset for all instants * @return the next transition after the specified instant, null if this is after the last transition */ public ZoneOffsetTransition nextTransition(Instant instant) { if (savingsInstantTransitions.length == 0) { return null; } long epochSec = instant.getEpochSecond(); // check if using last rules if (epochSec >= savingsInstantTransitions[savingsInstantTransitions.length - 1]) { if (lastRules.length == 0) { return null; } // search year the instant is in int year = findYear(epochSec, wallOffsets[wallOffsets.length - 1]); ZoneOffsetTransition[] transArray = findTransitionArray(year); for (ZoneOffsetTransition trans : transArray) { if (epochSec < trans.toEpochSecond()) { return trans; } } // use first from following year if (year < Year.MAX_VALUE) { transArray = findTransitionArray(year + 1); return transArray[0]; } return null; } // using historic rules int index = Arrays.binarySearch(savingsInstantTransitions, epochSec); if (index < 0) { index = -index - 1; // switched value is the next transition } else { index += 1; // exact match, so need to add one to get the next } return new ZoneOffsetTransition(savingsInstantTransitions[index], wallOffsets[index], wallOffsets[index + 1]); } /** * Gets the previous transition before the specified instant. *

* This returns details of the previous transition after the specified instant. * For example, if the instant represents a point where "summer" daylight saving time * applies, then the method will return the transition from the previous "winter" time. * * @param instant the instant to get the previous transition after, not null, but null * may be ignored if the rules have a single offset for all instants * @return the previous transition after the specified instant, null if this is before the first transition */ public ZoneOffsetTransition previousTransition(Instant instant) { if (savingsInstantTransitions.length == 0) { return null; } long epochSec = instant.getEpochSecond(); if (instant.getNano() > 0 && epochSec < Long.MAX_VALUE) { epochSec += 1; // allow rest of method to only use seconds } // check if using last rules long lastHistoric = savingsInstantTransitions[savingsInstantTransitions.length - 1]; if (lastRules.length > 0 && epochSec > lastHistoric) { // search year the instant is in ZoneOffset lastHistoricOffset = wallOffsets[wallOffsets.length - 1]; int year = findYear(epochSec, lastHistoricOffset); ZoneOffsetTransition[] transArray = findTransitionArray(year); for (int i = transArray.length - 1; i >= 0; i--) { if (epochSec > transArray[i].toEpochSecond()) { return transArray[i]; } } // use last from preceding year int lastHistoricYear = findYear(lastHistoric, lastHistoricOffset); if (--year > lastHistoricYear) { transArray = findTransitionArray(year); return transArray[transArray.length - 1]; } // drop through } // using historic rules int index = Arrays.binarySearch(savingsInstantTransitions, epochSec); if (index < 0) { index = -index - 1; } if (index <= 0) { return null; } return new ZoneOffsetTransition(savingsInstantTransitions[index - 1], wallOffsets[index - 1], wallOffsets[index]); } private int findYear(long epochSecond, ZoneOffset offset) { // inline for performance long localSecond = epochSecond + offset.getTotalSeconds(); long localEpochDay = Math.floorDiv(localSecond, 86400); return LocalDate.ofEpochDay(localEpochDay).getYear(); } /** * Gets the complete list of fully defined transitions. *

* The complete set of transitions for this rules instance is defined by this method * and {@link #getTransitionRules()}. This method returns those transitions that have * been fully defined. These are typically historical, but may be in the future. *

* The list will be empty for fixed offset rules and for any time-zone where there has * only ever been a single offset. The list will also be empty if the transition rules are unknown. * * @return an immutable list of fully defined transitions, not null */ public List getTransitions() { List list = new ArrayList<>(); for (int i = 0; i < savingsInstantTransitions.length; i++) { list.add(new ZoneOffsetTransition(savingsInstantTransitions[i], wallOffsets[i], wallOffsets[i + 1])); } return Collections.unmodifiableList(list); } /** * Gets the list of transition rules for years beyond those defined in the transition list. *

* The complete set of transitions for this rules instance is defined by this method * and {@link #getTransitions()}. This method returns instances of {@link ZoneOffsetTransitionRule} * that define an algorithm for when transitions will occur. *

* For any given {@code ZoneRules}, this list contains the transition rules for years * beyond those years that have been fully defined. These rules typically refer to future * daylight saving time rule changes. *

* If the zone defines daylight savings into the future, then the list will normally * be of size two and hold information about entering and exiting daylight savings. * If the zone does not have daylight savings, or information about future changes * is uncertain, then the list will be empty. *

* The list will be empty for fixed offset rules and for any time-zone where there is no * daylight saving time. The list will also be empty if the transition rules are unknown. * * @return an immutable list of transition rules, not null */ public List getTransitionRules() { return Collections.unmodifiableList(Arrays.asList(lastRules)); } /** * Checks if this set of rules equals another. *

* Two rule sets are equal if they will always result in the same output * for any given input instant or local date-time. * Rules from two different groups may return false even if they are in fact the same. *

* This definition should result in implementations comparing their entire state. * * @param otherRules the other rules, null returns false * @return true if this rules is the same as that specified */ @Override public boolean equals(Object otherRules) { if (this == otherRules) { return true; } if (otherRules instanceof ZoneRules) { ZoneRules other = (ZoneRules) otherRules; return Arrays.equals(standardTransitions, other.standardTransitions) && Arrays.equals(standardOffsets, other.standardOffsets) && Arrays.equals(savingsInstantTransitions, other.savingsInstantTransitions) && Arrays.equals(wallOffsets, other.wallOffsets) && Arrays.equals(lastRules, other.lastRules); } return false; } /** * Returns a suitable hash code given the definition of {@code #equals}. * * @return the hash code */ @Override public int hashCode() { return Arrays.hashCode(standardTransitions) ^ Arrays.hashCode(standardOffsets) ^ Arrays.hashCode(savingsInstantTransitions) ^ Arrays.hashCode(wallOffsets) ^ Arrays.hashCode(lastRules); } /** * Returns a string describing this object. * * @return a string for debugging, not null */ @Override public String toString() { return "ZoneRules[currentStandardOffset=" + standardOffsets[standardOffsets.length - 1] + "]"; } }