基于Java8的日期时间工具类DateTimeFormatter

原文：https://blog.csdn.net/qq_36596145/article/details/85331002

import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoField;
import java.util.Date;

/**
 * 基于Java8的时间工具类
 *
 * @author keji
 * @version $Id: DateUtil.java, v 0.1 2018-12-28 14:11 keji Exp $
 */
public class DateUtil {

    /**
     * 例如:2018-12-28
     */
    public static final String DATE = "yyyy-MM-dd";
    /**
     * 例如:2018-12-28 10:00:00
     */
    public static final String DATE_TIME = "yyyy-MM-dd HH:mm:ss";
    /**
     * 例如:10:00:00
     */
    public static final String TIME = "HHmmss";
    /**
     * 例如:10:00
     */
    public static final String TIME_WITHOUT_SECOND = "HH:mm";

    /**
     * 例如:2018-12-28 10:00
     */
    public static final String DATE_TIME_WITHOUT_SECONDS = "yyyy-MM-dd HH:mm";

    /**
     * 获取年
     *
     * @return 年
     */
    public static int getYear() {
        LocalTime localTime = LocalTime.now();
        return localTime.get(ChronoField.YEAR);
    }

    /**
     * 获取月份
     *
     * @return 月份
     */
    public static int getMonth() {
        LocalTime localTime = LocalTime.now();
        return localTime.get(ChronoField.MONTH_OF_YEAR);
    }

    /**
     * 获取某月的第几天
     *
     * @return 几号
     */
    public static int getMonthOfDay() {
        LocalTime localTime = LocalTime.now();
        return localTime.get(ChronoField.DAY_OF_MONTH);
    }

    /**
     * 格式化日期为字符串
     *
     * @param date date
     * @param pattern 格式
     * @return 日期字符串
     */
    public static String format(Date date,String pattern){

        Instant instant = date.toInstant();

        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());

        return localDateTime.format(DateTimeFormatter.ofPattern(pattern));
    }

    /**
     * 解析字符串日期为Date
     *
     * @param dateStr 日期字符串
     * @param pattern 格式
     * @return Date
     */
    public static Date parse(String dateStr, String pattern) {

        LocalDateTime localDateTime = LocalDateTime.parse(dateStr, DateTimeFormatter.ofPattern(pattern));
        Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
        return Date.from(instant);
    }

    /**
     * 为Date增加分钟,减传负数
     *
     * @param date        日期
     * @param plusMinutes 要增加的分钟数
     * @return 新的日期
     */
    public static Date addMinutes(Date date, Long plusMinutes) {
        LocalDateTime dateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
        LocalDateTime newDateTime = dateTime.plusMinutes(plusMinutes);
        return Date.from(newDateTime.atZone(ZoneId.systemDefault()).toInstant());
    }

    /**
     * 增加时间
     *
     * @param date date
     * @param hour 要增加的小时数
     * @return new date
     */
    public static Date addHour(Date date, Long hour) {
        LocalDateTime dateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
        LocalDateTime localDateTime = dateTime.plusHours(hour);
        return Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
    }

    /**
     * @return 返回当天的起始时间
     */
    public static Date getStartTime() {

        LocalDateTime now = LocalDateTime.now().withHour(0).withMinute(0).withSecond(0);
        return localDateTime2Date(now);
    }

    /**
     * @return 返回当天的结束时间
     */
    public static Date getEndTime() {
        LocalDateTime now = LocalDateTime.now().withHour(23).withMinute(59).withSecond(59).withNano(999);
        return localDateTime2Date(now);
    }

    /**
     * 减月份
     *
     * @param monthsToSubtract 月份
     * @return Date
     */
    public static Date minusMonths(long monthsToSubtract){
        LocalDate localDate = LocalDate.now().minusMonths(monthsToSubtract);

        return localDate2Date(localDate);
    }

    /**
     * LocalDate类型转为Date
     *
     * @param localDate LocalDate object
     * @return Date object
     */
    public static Date localDate2Date(LocalDate localDate) {

        ZonedDateTime zonedDateTime = localDate.atStartOfDay(ZoneId.systemDefault());

        return Date.from(zonedDateTime.toInstant());
    }

    /**
     * LocalDateTime类型转为Date
     *
     * @param localDateTime LocalDateTime object
     * @return Date object
     */
    public static Date localDateTime2Date(LocalDateTime localDateTime) {
        return Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
    }

    /**
     * 查询当前年的第一天
     *
     * @param pattern 格式，默认格式yyyyMMdd
     * @return 20190101
     */
    public static String getFirstDayOfCurrentYear(String pattern) {
        LocalDateTime localDateTime = LocalDateTime.now().withMonth(1).withDayOfMonth(1);

        if (StringUtils.isEmpty(pattern)) {
            pattern = "yyyyMMdd";
        }

        return format(localDateTime2Date(localDateTime), pattern);
    }

    /**
     * 查询前一年最后一个月第一天
     *
     * @param pattern 格式，默认格式yyyyMMdd
     * @return 20190101
     */
    public static String getLastMonthFirstDayOfPreviousYear(String pattern) {
        LocalDateTime localDateTime = LocalDateTime.now().minusYears(1L).withMonth(12).withDayOfMonth(1);

        if (StringUtils.isEmpty(pattern)) {
            pattern = "yyyyMMdd";
        }

        return format(localDateTime2Date(localDateTime), pattern);
    }

    /**
     * 查询前一年最后一个月第一天
     *
     * @param pattern 格式，默认格式yyyyMMdd
     * @return 20190101
     */
    public static String getLastMonthLastDayOfPreviousYear(String pattern) {
        LocalDateTime localDateTime = LocalDateTime.now().minusYears(1L).with(TemporalAdjusters.lastDayOfYear());

        if (StringUtils.isEmpty(pattern)) {
            pattern = "yyyyMMdd";
        }

        return format(localDateTime2Date(localDateTime), pattern);
    }

    /**
     * 获取当前日期
     *
     * @param pattern 格式，默认格式yyyyMMdd
     * @return 20190101
     */
    public static String getCurrentDay(String pattern) {
        LocalDateTime localDateTime = LocalDateTime.now();

        if (StringUtils.isEmpty(pattern)) {
            pattern = "yyyyMMdd";
        }

        return format(localDateTime2Date(localDateTime), pattern);
    }
}