| /* |
| * Copyright (c) 2021, 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. |
| */ |
| package java.time; |
| |
| import java.time.Clock.SourceClock; |
| import java.time.Clock.SystemInstantSource; |
| import java.util.Objects; |
| |
| /** |
| * Provides access to the current instant. |
| * <p> |
| * Instances of this interface are used to access a pluggable representation of the current instant. |
| * For example, {@code InstantSource} can be used instead of {@link System#currentTimeMillis()}. |
| * <p> |
| * The primary purpose of this abstraction is to allow alternate instant sources 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> |
| * As such, this interface does not guarantee the result actually represents the current instant |
| * on the time-line. Instead, it allows the application to provide a controlled view as to what |
| * the current instant is. |
| * <p> |
| * Best practice for applications is to pass an {@code InstantSource} into any method |
| * that requires the current instant. A dependency injection framework is one |
| * way to achieve this: |
| * <pre> |
| * public class MyBean { |
| * private InstantSource source; // dependency inject |
| * ... |
| * public void process(Instant endInstant) { |
| * if (source.instant().isAfter(endInstant) { |
| * ... |
| * } |
| * } |
| * } |
| * </pre> |
| * This approach allows an alternative source, such as {@link #fixed(Instant) fixed} |
| * or {@link #offset(InstantSource, Duration) offset} to be used during testing. |
| * <p> |
| * The {@code system} factory method provides a source based on the best available |
| * system clock. This may use {@link System#currentTimeMillis()}, or a higher |
| * resolution clock if one is available. |
| * |
| * @implSpec |
| * This interface must be implemented with care to ensure other classes operate correctly. |
| * All implementations must be thread-safe - a single instance must be capable of be invoked |
| * from multiple threads without negative consequences such as race conditions. |
| * <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 InstantSource} 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 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 implementation provided here is based on the same underlying system clock |
| * as {@link System#currentTimeMillis()}, but may have a precision finer than |
| * milliseconds if available. |
| * However, little to no guarantee is provided about the accuracy of the |
| * underlying system clock. Applications requiring a more accurate system clock must |
| * implement this abstract class themselves using a different external system clock, |
| * such as an NTP server. |
| * |
| * @since 17 |
| */ |
| public interface InstantSource { |
| |
| /** |
| * Obtains a source that returns the current instant using the best available |
| * system clock. |
| * <p> |
| * This source is based on the best available system clock. This may use |
| * {@link System#currentTimeMillis()}, or a higher resolution system clock if |
| * one is available. |
| * <p> |
| * The returned implementation is immutable, thread-safe and |
| * {@code Serializable}. |
| * |
| * @return a source that uses the best available system clock, not null |
| */ |
| static InstantSource system() { |
| return SystemInstantSource.INSTANCE; |
| } |
| |
| //------------------------------------------------------------------------- |
| /** |
| * Obtains a source that returns instants from the specified source truncated to |
| * the nearest occurrence of the specified duration. |
| * <p> |
| * This source will only tick as per the specified duration. Thus, if the |
| * duration is half a second, the source 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 source. |
| * <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 |
| * source will be later than that observed directly via the underlying source. |
| * <p> |
| * The returned implementation is immutable, thread-safe and |
| * {@code Serializable} providing that the base source is. |
| * |
| * @param baseSource the base source to base the ticking source on, not null |
| * @param tickDuration the duration of each visible tick, not negative, not null |
| * @return a source 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 |
| */ |
| static InstantSource tick(InstantSource baseSource, Duration tickDuration) { |
| Objects.requireNonNull(baseSource, "baseSource"); |
| return Clock.tick(baseSource.withZone(ZoneOffset.UTC), tickDuration); |
| } |
| |
| //----------------------------------------------------------------------- |
| /** |
| * Obtains a source that always returns the same instant. |
| * <p> |
| * This source simply returns the specified instant. |
| * As such, it is not a source that represents the current instant. |
| * The main use case for this is in testing, where the fixed source ensures |
| * tests are not dependent on the current source. |
| * <p> |
| * The returned implementation is immutable, thread-safe and {@code Serializable}. |
| * |
| * @param fixedInstant the instant to use, not null |
| * @return a source that always returns the same instant, not null |
| */ |
| static InstantSource fixed(Instant fixedInstant) { |
| return Clock.fixed(fixedInstant, ZoneOffset.UTC); |
| } |
| |
| //------------------------------------------------------------------------- |
| /** |
| * Obtains a source that returns instants from the specified source with the |
| * specified duration added. |
| * <p> |
| * This source wraps another source, 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 source. |
| * <p> |
| * The returned implementation is immutable, thread-safe and {@code Serializable} |
| * providing that the base source is. |
| * |
| * @param baseSource the base source to add the duration to, not null |
| * @param offsetDuration the duration to add, not null |
| * @return a source based on the base source with the duration added, not null |
| */ |
| static InstantSource offset(InstantSource baseSource, Duration offsetDuration) { |
| Objects.requireNonNull(baseSource, "baseSource"); |
| return Clock.offset(baseSource.withZone(ZoneOffset.UTC), offsetDuration); |
| } |
| |
| //----------------------------------------------------------------------- |
| /** |
| * Gets the current instant of the source. |
| * <p> |
| * This returns an instant representing the current instant as defined by the source. |
| * |
| * @return the current instant from this source, not null |
| * @throws DateTimeException if the instant cannot be obtained, not thrown by most implementations |
| */ |
| Instant instant(); |
| |
| //------------------------------------------------------------------------- |
| /** |
| * Gets the current millisecond instant of the source. |
| * <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 source in high performance use cases |
| * where the creation of an object would be unacceptable. |
| * |
| * @implSpec |
| * The default implementation calls {@link #instant()}. |
| * |
| * @return the current millisecond instant from this source, 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 |
| */ |
| default long millis() { |
| return instant().toEpochMilli(); |
| } |
| |
| //----------------------------------------------------------------------- |
| /** |
| * Returns a clock with the specified time-zone. |
| * <p> |
| * This returns a {@link Clock}, which is an extension of this interface |
| * that combines this source and the specified time-zone. |
| * <p> |
| * The returned implementation is immutable, thread-safe and {@code Serializable} |
| * providing that this source is. |
| * |
| * @implSpec |
| * The default implementation returns an immutable, thread-safe and |
| * {@code Serializable} subclass of {@link Clock} that combines this |
| * source and the specified zone. |
| * |
| * @param zone the time-zone to use, not null |
| * @return a clock based on this source with the specified time-zone, not null |
| */ |
| default Clock withZone(ZoneId zone) { |
| return new SourceClock(this, zone); |
| } |
| |
| } |