【hutool】使用问题

如何将Date转化为LocalDateTime

package cn.hutool.core.date;

public class LocalDateTimeUtil {
	/**
	 * {@link Date}转{@link LocalDateTime}，使用默认时区
	 *
	 * @param date Date对象
	 * @return {@link LocalDateTime}
	 */
	public static LocalDateTime of(Date date) {
		if (null == date) {
			return null;
		}

		if (date instanceof DateTime) {
			return of(date.toInstant(), ((DateTime) date).getZoneId());
		}
		return of(date.toInstant());
	}
}

如何将LocalDateTime、LocalDate转化为Date

• 方案1

对纯原生的转化方式Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant())进行简单封装。即先使用TemporalAccessorUtil#toInstant(TemporalAccessor)将LocalDateTime转化为Instant（底层就是执行localDateTime.atZone(ZoneId.systemDefault()).toInstant()）

package cn.hutool.core.date;

public class TemporalAccessorUtil extends TemporalUtil{
	/**
	 * {@link TemporalAccessor}转换为 {@link Instant}对象
	 *
	 * @param temporalAccessor Date对象
	 * @return {@link Instant}对象
	 * @since 5.3.10
	 */
	public static Instant toInstant(TemporalAccessor temporalAccessor) {
		if (null == temporalAccessor) {
			return null;
		}

		Instant result;
		if (temporalAccessor instanceof Instant) {
			result = (Instant) temporalAccessor;
		} else if (temporalAccessor instanceof LocalDateTime) {
			result = ((LocalDateTime) temporalAccessor).atZone(ZoneId.systemDefault()).toInstant();
		} else if (temporalAccessor instanceof ZonedDateTime) {
			result = ((ZonedDateTime) temporalAccessor).toInstant();
		} else if (temporalAccessor instanceof OffsetDateTime) {
			result = ((OffsetDateTime) temporalAccessor).toInstant();
		} else if (temporalAccessor instanceof LocalDate) {
			result = ((LocalDate) temporalAccessor).atStartOfDay(ZoneId.systemDefault()).toInstant();
		} else if (temporalAccessor instanceof LocalTime) {
			// 指定本地时间转换 为Instant，取当天日期
			result = ((LocalTime) temporalAccessor).atDate(LocalDate.now()).atZone(ZoneId.systemDefault()).toInstant();
		} else if (temporalAccessor instanceof OffsetTime) {
			// 指定本地时间转换 为Instant，取当天日期
			result = ((OffsetTime) temporalAccessor).atDate(LocalDate.now()).toInstant();
		} else {
			// issue#1891@Github
			// Instant.from不能完成日期转换
			//result = Instant.from(temporalAccessor);
			result = toInstant(LocalDateTimeUtil.of(temporalAccessor));
		}

		return result;
	}
}

再使用Date#from(Instant)

package java.util;

public class Date implements java.io.Serializable, Cloneable, Comparable<Date> {
	/**
     * Obtains an instance of {@code Date} from an {@code Instant} object.
     * 

     * {@code Instant} uses a precision of nanoseconds, whereas {@code Date}
     * uses a precision of milliseconds.  The conversion will truncate any
     * excess precision information as though the amount in nanoseconds was
     * subject to integer division by one million.
     * 

     * {@code Instant} can store points on the time-line further in the future
     * and further in the past than {@code Date}. In this scenario, this method
     * will throw an exception.
     *
     * @param instant  the instant to convert
     * @return a {@code Date} representing the same point on the time-line as
     *  the provided instant
     * @exception NullPointerException if {@code instant} is null.
     * @exception IllegalArgumentException if the instant is too large to
     *  represent as a {@code Date}
     * @since 1.8
     */
    public static Date from(Instant instant) {
        try {
            return new Date(instant.toEpochMilli());
        } catch (ArithmeticException ex) {
            throw new IllegalArgumentException(ex);
        }
    }
}

• 方案2

DateTime类继承于java.util.Date类，为Date类扩展了众多简便方法，这些方法多是DateUtil静态方法的对象表现形式，使用DateTime对象可以完全替代开发中Date对象的使用。

package cn.hutool.core.date;

public class DateUtil extends CalendarUtil {
	/**
	 * {@link TemporalAccessor}类型时间转为{@link DateTime}

	 * 始终根据已有{@link TemporalAccessor} 产生新的{@link DateTime}对象
	 *
	 * @param temporalAccessor {@link TemporalAccessor},常用子类： {@link LocalDateTime}、 LocalDate
	 * @return 时间对象
	 * @since 5.0.0
	 */
	public static DateTime date(TemporalAccessor temporalAccessor) {
		return new DateTime(temporalAccessor);
	}
}

• 示例

public class Test {
	public static void main(String[] args) {
        final LocalDateTime localDateTime = LocalDateTime.of(2022, 5, 9, 11, 36);
        final Date date1 = Date.from(TemporalAccessorUtil.toInstant(localDateTime));
        final DateTime date2 = DateUtil.date(localDateTime);
    }
}