Java example source code file (Clock.java)
The Clock.java Java example source code
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* file:
*
* Copyright (c) 2007-2012, Stephen Colebourne & Michael Nascimento Santos
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package java.time;
import static java.time.LocalTime.NANOS_PER_MINUTE;
import static java.time.LocalTime.NANOS_PER_SECOND;
import java.io.Serializable;
import java.util.Objects;
import java.util.TimeZone;
/**
* A clock providing access to the current instant, date and time using a time-zone.
* <p>
* Instances of this class are used to find the current instant, which can be
* interpreted using the stored time-zone to find the current date and time.
* As such, a clock can be used instead of {@link System#currentTimeMillis()}
* and {@link TimeZone#getDefault()}.
* <p>
* Use of a {@code Clock} is optional. All key date-time classes also have a
* {@code now()} factory method that uses the system clock in the default time zone.
* The primary purpose of this abstraction is to allow alternate clocks to be
* plugged in as and when required. Applications use an object to obtain the
* current time rather than a static method. This can simplify testing.
* <p>
* Best practice for applications is to pass a {@code Clock} into any method
* that requires the current instant. A dependency injection framework is one
* way to achieve this:
* <pre>
* public class MyBean {
* private Clock clock; // dependency inject
* ...
* public void process(LocalDate eventDate) {
* if (eventDate.isBefore(LocalDate.now(clock)) {
* ...
* }
* }
* }
* </pre>
* This approach allows an alternate clock, such as {@link #fixed(Instant, ZoneId) fixed}
* or {@link #offset(Clock, Duration) offset} to be used during testing.
* <p>
* The {@code system} factory methods provide clocks based on the best available
* system clock This may use {@link System#currentTimeMillis()}, or a higher
* resolution clock if one is available.
*
* @implSpec
* This abstract class must be implemented with care to ensure other operate correctly.
* All implementations that can be instantiated must be final, immutable and thread-safe.
* <p>
* The principal methods are defined to allow the throwing of an exception.
* In normal use, no exceptions will be thrown, however one possible implementation would be to
* obtain the time from a central time server across the network. Obviously, in this case the
* lookup could fail, and so the method is permitted to throw an exception.
* <p>
* The returned instants from {@code Clock} work on a time-scale that ignores leap seconds,
* as described in {@link Instant}. If the implementation wraps a source that provides leap
* second information, then a mechanism should be used to "smooth" the leap second.
* The Java Time-Scale mandates the use of UTC-SLS, however clock implementations may choose
* how accurate they are with the time-scale so long as they document how they work.
* Implementations are therefore not required to actually perform the UTC-SLS slew or to
* otherwise be aware of leap seconds.
* <p>
* Implementations should implement {@code Serializable} wherever possible and must
* document whether or not they do support serialization.
*
* @implNote
* The clock implementation provided here is based on {@link System#currentTimeMillis()}.
* That method provides little to no guarantee about the accuracy of the clock.
* Applications requiring a more accurate clock must implement this abstract class
* themselves using a different external clock, such as an NTP server.
*
* @since 1.8
*/
public abstract class Clock {
/**
* Obtains a clock that returns the current instant using the best available
* system clock, converting to date and time using the UTC time-zone.
* <p>
* This clock, rather than {@link #systemDefaultZone()}, should be used when
* you need the current instant without the date or time.
* <p>
* This clock is based on the best available system clock.
* This may use {@link System#currentTimeMillis()}, or a higher resolution
* clock if one is available.
* <p>
* Conversion from instant to date or time uses the {@linkplain ZoneOffset#UTC UTC time-zone}.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}.
* It is equivalent to {@code system(ZoneOffset.UTC)}.
*
* @return a clock that uses the best available system clock in the UTC zone, not null
*/
public static Clock systemUTC() {
return new SystemClock(ZoneOffset.UTC);
}
/**
* Obtains a clock that returns the current instant using the best available
* system clock, converting to date and time using the default time-zone.
* <p>
* This clock is based on the best available system clock.
* This may use {@link System#currentTimeMillis()}, or a higher resolution
* clock if one is available.
* <p>
* Using this method hard codes a dependency to the default time-zone into your application.
* It is recommended to avoid this and use a specific time-zone whenever possible.
* The {@link #systemUTC() UTC clock} should be used when you need the current instant
* without the date or time.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}.
* It is equivalent to {@code system(ZoneId.systemDefault())}.
*
* @return a clock that uses the best available system clock in the default zone, not null
* @see ZoneId#systemDefault()
*/
public static Clock systemDefaultZone() {
return new SystemClock(ZoneId.systemDefault());
}
/**
* Obtains a clock that returns the current instant using best available
* system clock.
* <p>
* This clock is based on the best available system clock.
* This may use {@link System#currentTimeMillis()}, or a higher resolution
* clock if one is available.
* <p>
* Conversion from instant to date or time uses the specified time-zone.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}.
*
* @param zone the time-zone to use to convert the instant to date-time, not null
* @return a clock that uses the best available system clock in the specified zone, not null
*/
public static Clock system(ZoneId zone) {
Objects.requireNonNull(zone, "zone");
return new SystemClock(zone);
}
//-------------------------------------------------------------------------
/**
* Obtains a clock that returns the current instant ticking in whole seconds
* using best available system clock.
* <p>
* This clock will always have the nano-of-second field set to zero.
* This ensures that the visible time ticks in whole seconds.
* The underlying clock is the best available system clock, equivalent to
* using {@link #system(ZoneId)}.
* <p>
* Implementations may use a caching strategy for performance reasons.
* As such, it is possible that the start of the second observed via this
* clock will be later than that observed directly via the underlying clock.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}.
* It is equivalent to {@code tick(system(zone), Duration.ofSeconds(1))}.
*
* @param zone the time-zone to use to convert the instant to date-time, not null
* @return a clock that ticks in whole seconds using the specified zone, not null
*/
public static Clock tickSeconds(ZoneId zone) {
return new TickClock(system(zone), NANOS_PER_SECOND);
}
/**
* Obtains a clock that returns the current instant ticking in whole minutes
* using best available system clock.
* <p>
* This clock will always have the nano-of-second and second-of-minute fields set to zero.
* This ensures that the visible time ticks in whole minutes.
* The underlying clock is the best available system clock, equivalent to
* using {@link #system(ZoneId)}.
* <p>
* Implementations may use a caching strategy for performance reasons.
* As such, it is possible that the start of the minute observed via this
* clock will be later than that observed directly via the underlying clock.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}.
* It is equivalent to {@code tick(system(zone), Duration.ofMinutes(1))}.
*
* @param zone the time-zone to use to convert the instant to date-time, not null
* @return a clock that ticks in whole minutes using the specified zone, not null
*/
public static Clock tickMinutes(ZoneId zone) {
return new TickClock(system(zone), NANOS_PER_MINUTE);
}
/**
* Obtains a clock that returns instants from the specified clock truncated
* to the nearest occurrence of the specified duration.
* <p>
* This clock will only tick as per the specified duration. Thus, if the duration
* is half a second, the clock will return instants truncated to the half second.
* <p>
* The tick duration must be positive. If it has a part smaller than a whole
* millisecond, then the whole duration must divide into one second without
* leaving a remainder. All normal tick durations will match these criteria,
* including any multiple of hours, minutes, seconds and milliseconds, and
* sensible nanosecond durations, such as 20ns, 250,000ns and 500,000ns.
* <p>
* A duration of zero or one nanosecond would have no truncation effect.
* Passing one of these will return the underlying clock.
* <p>
* Implementations may use a caching strategy for performance reasons.
* As such, it is possible that the start of the requested duration observed
* via this clock will be later than that observed directly via the underlying clock.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}
* providing that the base clock is.
*
* @param baseClock the base clock to base the ticking clock on, not null
* @param tickDuration the duration of each visible tick, not negative, not null
* @return a clock that ticks in whole units of the duration, not null
* @throws IllegalArgumentException if the duration is negative, or has a
* part smaller than a whole millisecond such that the whole duration is not
* divisible into one second
* @throws ArithmeticException if the duration is too large to be represented as nanos
*/
public static Clock tick(Clock baseClock, Duration tickDuration) {
Objects.requireNonNull(baseClock, "baseClock");
Objects.requireNonNull(tickDuration, "tickDuration");
if (tickDuration.isNegative()) {
throw new IllegalArgumentException("Tick duration must not be negative");
}
long tickNanos = tickDuration.toNanos();
if (tickNanos % 1000_000 == 0) {
// ok, no fraction of millisecond
} else if (1000_000_000 % tickNanos == 0) {
// ok, divides into one second without remainder
} else {
throw new IllegalArgumentException("Invalid tick duration");
}
if (tickNanos <= 1) {
return baseClock;
}
return new TickClock(baseClock, tickNanos);
}
//-----------------------------------------------------------------------
/**
* Obtains a clock that always returns the same instant.
* <p>
* This clock simply returns the specified instant.
* As such, it is not a clock in the conventional sense.
* The main use case for this is in testing, where the fixed clock ensures
* tests are not dependent on the current clock.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}.
*
* @param fixedInstant the instant to use as the clock, not null
* @param zone the time-zone to use to convert the instant to date-time, not null
* @return a clock that always returns the same instant, not null
*/
public static Clock fixed(Instant fixedInstant, ZoneId zone) {
Objects.requireNonNull(fixedInstant, "fixedInstant");
Objects.requireNonNull(zone, "zone");
return new FixedClock(fixedInstant, zone);
}
//-------------------------------------------------------------------------
/**
* Obtains a clock that returns instants from the specified clock with the
* specified duration added
* <p>
* This clock wraps another clock, returning instants that are later by the
* specified duration. If the duration is negative, the instants will be
* earlier than the current date and time.
* The main use case for this is to simulate running in the future or in the past.
* <p>
* A duration of zero would have no offsetting effect.
* Passing zero will return the underlying clock.
* <p>
* The returned implementation is immutable, thread-safe and {@code Serializable}
* providing that the base clock is.
*
* @param baseClock the base clock to add the duration to, not null
* @param offsetDuration the duration to add, not null
* @return a clock based on the base clock with the duration added, not null
*/
public static Clock offset(Clock baseClock, Duration offsetDuration) {
Objects.requireNonNull(baseClock, "baseClock");
Objects.requireNonNull(offsetDuration, "offsetDuration");
if (offsetDuration.equals(Duration.ZERO)) {
return baseClock;
}
return new OffsetClock(baseClock, offsetDuration);
}
//-----------------------------------------------------------------------
/**
* Constructor accessible by subclasses.
*/
protected Clock() {
}
//-----------------------------------------------------------------------
/**
* Gets the time-zone being used to create dates and times.
* <p>
* A clock will typically obtain the current instant and then convert that
* to a date or time using a time-zone. This method returns the time-zone used.
*
* @return the time-zone being used to interpret instants, not null
*/
public abstract ZoneId getZone();
/**
* Returns a copy of this clock with a different time-zone.
* <p>
* A clock will typically obtain the current instant and then convert that
* to a date or time using a time-zone. This method returns a clock with
* similar properties but using a different time-zone.
*
* @param zone the time-zone to change to, not null
* @return a clock based on this clock with the specified time-zone, not null
*/
public abstract Clock withZone(ZoneId zone);
//-------------------------------------------------------------------------
/**
* Gets the current millisecond instant of the clock.
* <p>
* This returns the millisecond-based instant, measured from 1970-01-01T00:00Z (UTC).
* This is equivalent to the definition of {@link System#currentTimeMillis()}.
* <p>
* Most applications should avoid this method and use {@link Instant} to represent
* an instant on the time-line rather than a raw millisecond value.
* This method is provided to allow the use of the clock in high performance use cases
* where the creation of an object would be unacceptable.
* <p>
* The default implementation currently calls {@link #instant}.
*
* @return the current millisecond instant from this clock, measured from
* the Java epoch of 1970-01-01T00:00Z (UTC), not null
* @throws DateTimeException if the instant cannot be obtained, not thrown by most implementations
*/
public long millis() {
return instant().toEpochMilli();
}
//-----------------------------------------------------------------------
/**
* Gets the current instant of the clock.
* <p>
* This returns an instant representing the current instant as defined by the clock.
*
* @return the current instant from this clock, not null
* @throws DateTimeException if the instant cannot be obtained, not thrown by most implementations
*/
public abstract Instant instant();
//-----------------------------------------------------------------------
/**
* Checks if this clock is equal to another clock.
* <p>
* Clocks should override this method to compare equals based on
* their state and to meet the contract of {@link Object#equals}.
* If not overridden, the behavior is defined by {@link Object#equals}
*
* @param obj the object to check, null returns false
* @return true if this is equal to the other clock
*/
@Override
public boolean equals(Object obj) {
return super.equals(obj);
}
/**
* A hash code for this clock.
* <p>
* Clocks should override this method based on
* their state and to meet the contract of {@link Object#hashCode}.
* If not overridden, the behavior is defined by {@link Object#hashCode}
*
* @return a suitable hash code
*/
@Override
public int hashCode() {
return super.hashCode();
}
//-----------------------------------------------------------------------
/**
* Implementation of a clock that always returns the latest time from
* {@link System#currentTimeMillis()}.
*/
static final class SystemClock extends Clock implements Serializable {
private static final long serialVersionUID = 6740630888130243051L;
private final ZoneId zone;
SystemClock(ZoneId zone) {
this.zone = zone;
}
@Override
public ZoneId getZone() {
return zone;
}
@Override
public Clock withZone(ZoneId zone) {
if (zone.equals(this.zone)) { // intentional NPE
return this;
}
return new SystemClock(zone);
}
@Override
public long millis() {
return System.currentTimeMillis();
}
@Override
public Instant instant() {
return Instant.ofEpochMilli(millis());
}
@Override
public boolean equals(Object obj) {
if (obj instanceof SystemClock) {
return zone.equals(((SystemClock) obj).zone);
}
return false;
}
@Override
public int hashCode() {
return zone.hashCode() + 1;
}
@Override
public String toString() {
return "SystemClock[" + zone + "]";
}
}
//-----------------------------------------------------------------------
/**
* Implementation of a clock that always returns the same instant.
* This is typically used for testing.
*/
static final class FixedClock extends Clock implements Serializable {
private static final long serialVersionUID = 7430389292664866958L;
private final Instant instant;
private final ZoneId zone;
FixedClock(Instant fixedInstant, ZoneId zone) {
this.instant = fixedInstant;
this.zone = zone;
}
@Override
public ZoneId getZone() {
return zone;
}
@Override
public Clock withZone(ZoneId zone) {
if (zone.equals(this.zone)) { // intentional NPE
return this;
}
return new FixedClock(instant, zone);
}
@Override
public long millis() {
return instant.toEpochMilli();
}
@Override
public Instant instant() {
return instant;
}
@Override
public boolean equals(Object obj) {
if (obj instanceof FixedClock) {
FixedClock other = (FixedClock) obj;
return instant.equals(other.instant) && zone.equals(other.zone);
}
return false;
}
@Override
public int hashCode() {
return instant.hashCode() ^ zone.hashCode();
}
@Override
public String toString() {
return "FixedClock[" + instant + "," + zone + "]";
}
}
//-----------------------------------------------------------------------
/**
* Implementation of a clock that adds an offset to an underlying clock.
*/
static final class OffsetClock extends Clock implements Serializable {
private static final long serialVersionUID = 2007484719125426256L;
private final Clock baseClock;
private final Duration offset;
OffsetClock(Clock baseClock, Duration offset) {
this.baseClock = baseClock;
this.offset = offset;
}
@Override
public ZoneId getZone() {
return baseClock.getZone();
}
@Override
public Clock withZone(ZoneId zone) {
if (zone.equals(baseClock.getZone())) { // intentional NPE
return this;
}
return new OffsetClock(baseClock.withZone(zone), offset);
}
@Override
public long millis() {
return Math.addExact(baseClock.millis(), offset.toMillis());
}
@Override
public Instant instant() {
return baseClock.instant().plus(offset);
}
@Override
public boolean equals(Object obj) {
if (obj instanceof OffsetClock) {
OffsetClock other = (OffsetClock) obj;
return baseClock.equals(other.baseClock) && offset.equals(other.offset);
}
return false;
}
@Override
public int hashCode() {
return baseClock.hashCode() ^ offset.hashCode();
}
@Override
public String toString() {
return "OffsetClock[" + baseClock + "," + offset + "]";
}
}
//-----------------------------------------------------------------------
/**
* Implementation of a clock that adds an offset to an underlying clock.
*/
static final class TickClock extends Clock implements Serializable {
private static final long serialVersionUID = 6504659149906368850L;
private final Clock baseClock;
private final long tickNanos;
TickClock(Clock baseClock, long tickNanos) {
this.baseClock = baseClock;
this.tickNanos = tickNanos;
}
@Override
public ZoneId getZone() {
return baseClock.getZone();
}
@Override
public Clock withZone(ZoneId zone) {
if (zone.equals(baseClock.getZone())) { // intentional NPE
return this;
}
return new TickClock(baseClock.withZone(zone), tickNanos);
}
@Override
public long millis() {
long millis = baseClock.millis();
return millis - Math.floorMod(millis, tickNanos / 1000_000L);
}
@Override
public Instant instant() {
if ((tickNanos % 1000_000) == 0) {
long millis = baseClock.millis();
return Instant.ofEpochMilli(millis - Math.floorMod(millis, tickNanos / 1000_000L));
}
Instant instant = baseClock.instant();
long nanos = instant.getNano();
long adjust = Math.floorMod(nanos, tickNanos);
return instant.minusNanos(adjust);
}
@Override
public boolean equals(Object obj) {
if (obj instanceof TickClock) {
TickClock other = (TickClock) obj;
return baseClock.equals(other.baseClock) && tickNanos == other.tickNanos;
}
return false;
}
@Override
public int hashCode() {
return baseClock.hashCode() ^ ((int) (tickNanos ^ (tickNanos >>> 32)));
}
@Override
public String toString() {
return "TickClock[" + baseClock + "," + Duration.ofNanos(tickNanos) + "]";
}
}
}
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