在开发过程中经常会用到日期相关的计算，这里进行总结，后续不断进行方法的增加。

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

/**
 * @Description 日期时间工具类
 * @Author Maverickos
 * @Date 2023-08-17
 */
public class DateTimeUtil {

    private static final String DATETIME_FORMATTER = "yyyyMMdd HH:mm:ss";
    private static final String DATE_FORMATTER = "yyyyMMdd";
    private static final String TIME_FORMATTER = "HHmmss";
    private static final String TIME_MILLISECOND_FORMATTER = "HHmmssSSS";

    public static class CurrDateTime {
        private Integer currDate = 0;
        private Integer currTime = 0;
        private Integer currMillisecond = 0;

        public Integer getCurrDate() {
            return currDate;
        }

        public void setCurrDate(Integer currDate) {
            this.currDate = currDate;
        }

        public Integer getCurrTime() {
            return currTime;
        }

        public void setCurrTime(Integer currTime) {
            this.currTime = currTime;
        }

        public Integer getCurrMillisecond() {
            return currMillisecond;
        }

        public void setCurrMillisecond(Integer currMillisecond) {
            this.currMillisecond = currMillisecond;
        }
    }

    public static void main(String[] args) {
        CurrDateTime currDateTime = getCurrDateTime();
        System.out.println("日期: " + currDateTime.getCurrDate());
        System.out.println("时间(秒): " + currDateTime.getCurrTime());
        System.out.println("时间(毫秒): " + currDateTime.getCurrMillisecond());

        System.out.println(addDate(currDateTime.getCurrDate(), -100));
    }

    /**
     * 获取当前日期和时间信息
     *
     * @return  获取当前日期、当前时间、当前秒、当前毫秒
     */
    public static CurrDateTime getCurrDateTime() {
        CurrDateTime currDateTime = new CurrDateTime();

        LocalDateTime now = LocalDateTime.now();
        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern(DATE_FORMATTER);
        DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern(TIME_FORMATTER);
        DateTimeFormatter timeMillisecondFormatter = DateTimeFormatter.ofPattern(TIME_MILLISECOND_FORMATTER);

        currDateTime.setCurrDate(Integer.valueOf(dateFormatter.format(now)));
        currDateTime.setCurrTime(Integer.valueOf(timeFormatter.format(now)));
        currDateTime.setCurrMillisecond(Integer.valueOf(timeMillisecondFormatter.format(now)));
        return currDateTime;
    }

    /**
     * 给定间隔天数，计算输入日期往前或往后对应的日期
     *
     * @param date  输入日期
     * @param interval  间隔天数
     * @return
     */
    public static Integer addDate(Integer date, Integer interval) {
        DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern(DATE_FORMATTER);
        // dateFormat此时输出格式为2001-01-01
        LocalDate dateFormat = LocalDate.parse(String.valueOf(date), dateFormatter);
        LocalDate nextDate = dateFormat.plusDays(interval);
        Integer result = Integer.valueOf(dateFormatter.format(nextDate));
        return result;
    }
}