DateTimeProvider.java

package com.example.todo.library.datetime;

import java.time.Clock;
import java.time.Instant;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.time.temporal.ChronoField;
import java.util.Objects;

public class DateTimeProvider {

  private final Clock clock;

  public DateTimeProvider(Clock clock) {
    Objects.requireNonNull(clock);
    this.clock = clock;
  }

  public Instant instant() {
    return clock.instant();
  }

  public ZonedDateTime now() {
    return ZonedDateTime.now(clock.getZone());
  }

  public ZonedDateTime now(ZoneId zoneId) {
    return ZonedDateTime.ofInstant(clock.instant(), zoneId);
  }

  public static void main(String[] args) {
    DateTimeProvider provider = new DateTimeProvider(Clock.system(ZoneId.of("Asia/Tokyo")));
    ZonedDateTime now = provider.now();
    ZoneOffset offset = now.getOffset();

    System.out.println(now);
    System.out.println(provider.now(ZoneId.of("UTC")));
    System.out.println(offset);
    System.out.println(offset.getId());
    System.out.println(offset.normalized());
    System.out.println(offset.range(ChronoField.OFFSET_SECONDS));
  }
}

output.txt

2018-07-19T17:21:46.667+09:00[Asia/Tokyo]
2018-07-19T08:21:46.667Z[UTC]
+09:00
+09:00
+09:00
-64800 - 64800