Period 计算日期之间的天数差------ 坑点*****

计算两个时间之间的天数：

LocalDateTime dateTime = LocalDateTime.ofInstant(Instant.ofEpochMilli(1528197133157L), ZoneId.systemDefault());
        LocalDate now = LocalDate.now();
        Period between = Period.between(dateTime.toLocalDate(), now);
        int days = between.getDays();
        System.out.println(days);

使用Period 你会发现，天数差不是想要的，是当月的天数差
具体的如下图：

求两个时间之间的天数差，正确的应该是：

LocalDateTime dateTime = LocalDateTime.ofInstant(Instant.ofEpochMilli(1528197133157L), ZoneId.systemDefault());
        LocalDate now = LocalDate.now();
        Period between = Period.between(dateTime.toLocalDate(), now);
        long between1 = ChronoUnit.DAYS.between(dateTime.toLocalDate(), now);
        long between2 = ChronoUnit.MONTHS.between(dateTime.toLocalDate(), now);

ChronoUnit 中有求两个时间之间的天数差，月份差
`public enum ChronoUnit implements TemporalUnit {

/**
 * Unit that represents the concept of a nanosecond, the smallest supported unit of time.
 * For the ISO calendar system, it is equal to the 1,000,000,000th part of the second unit.
 */
NANOS("Nanos", Duration.ofNanos(1)),
/**
 * Unit that represents the concept of a microsecond.
 * For the ISO calendar system, it is equal to the 1,000,000th part of the second unit.
 */
MICROS("Micros", Duration.ofNanos(1000)),
/**
 * Unit that represents the concept of a millisecond.
 * For the ISO calendar system, it is equal to the 1000th part of the second unit.
 */
MILLIS("Millis", Duration.ofNanos(1000_000)),
/**
 * Unit that represents the concept of a second.
 * For the ISO calendar system, it is equal to the second in the SI system
 * of units, except around a leap-second.
 */
SECONDS("Seconds", Duration.ofSeconds(1)),
/**
 * Unit that represents the concept of a minute.
 * For the ISO calendar system, it is equal to 60 seconds.
 */
MINUTES("Minutes", Duration.ofSeconds(60)),
/**
 * Unit that represents the concept of an hour.
 * For the ISO calendar system, it is equal to 60 minutes.
 */
HOURS("Hours", Duration.ofSeconds(3600)),
/**
 * Unit that represents the concept of half a day, as used in AM/PM.
 * For the ISO calendar system, it is equal to 12 hours.
 */
HALF_DAYS("HalfDays", Duration.ofSeconds(43200)),
/**
 * Unit that represents the concept of a day.
 * For the ISO calendar system, it is the standard day from midnight to midnight.
 * The estimated duration of a day is {@code 24 Hours}.
 * <p>
 * When used with other calendar systems it must correspond to the day defined by
 * the rising and setting of the Sun on Earth. It is not required that days begin
 * at midnight - when converting between calendar systems, the date should be
 * equivalent at midday.
 */
DAYS("Days", Duration.ofSeconds(86400)),
/**
 * Unit that represents the concept of a week.
 * For the ISO calendar system, it is equal to 7 days.
 * <p>
 * When used with other calendar systems it must correspond to an integral number of days.
 */
WEEKS("Weeks", Duration.ofSeconds(7 * 86400L)),
/**
 * Unit that represents the concept of a month.
 * For the ISO calendar system, the length of the month varies by month-of-year.
 * The estimated duration of a month is one twelfth of {@code 365.2425 Days}.
 * <p>
 * When used with other calendar systems it must correspond to an integral number of days.
 */
MONTHS("Months", Duration.ofSeconds(31556952L / 12)),
/**
 * Unit that represents the concept of a year.
 * For the ISO calendar system, it is equal to 12 months.
 * The estimated duration of a year is {@code 365.2425 Days}.
 * <p>
 * When used with other calendar systems it must correspond to an integral number of days
 * or months roughly equal to a year defined by the passage of the Earth around the Sun.
 */
YEARS("Years", Duration.ofSeconds(31556952L)),
/**
 * Unit that represents the concept of a decade.
 * For the ISO calendar system, it is equal to 10 years.
 * <p>
 * When used with other calendar systems it must correspond to an integral number of days
 * and is normally an integral number of years.
 */
DECADES("Decades", Duration.ofSeconds(31556952L * 10L)),
/**
 * Unit that represents the concept of a century.
 * For the ISO calendar system, it is equal to 100 years.
 * <p>
 * When used with other calendar systems it must correspond to an integral number of days
 * and is normally an integral number of years.
 */
CENTURIES("Centuries", Duration.ofSeconds(31556952L * 100L)),
/**
 * Unit that represents the concept of a millennium.
 * For the ISO calendar system, it is equal to 1000 years.
 * <p>
 * When used with other calendar systems it must correspond to an integral number of days
 * and is normally an integral number of years.
 */
MILLENNIA("Millennia", Duration.ofSeconds(31556952L * 1000L)),
/**
 * Unit that represents the concept of an era.
 * The ISO calendar system doesn't have eras thus it is impossible to add
 * an era to a date or date-time.
 * The estimated duration of the era is artificially defined as {@code 1,000,000,000 Years}.
 * <p>
 * When used with other calendar systems there are no restrictions on the unit.
 */
ERAS("Eras", Duration.ofSeconds(31556952L * 1000_000_000L)),
/**
 * Artificial unit that represents the concept of forever.
 * This is primarily used with {@link TemporalField} to represent unbounded fields
 * such as the year or era.
 * The estimated duration of the era is artificially defined as the largest duration
 * supported by {@code Duration}.
 */
FOREVER("Forever", Duration.ofSeconds(Long.MAX_VALUE, 999_999_999));

根据自己的需要计算时间