日期转换工具类：由TimeStamp时间戳转换为日期格式的字符串

import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

@Slf4j
public class DateTimeUtil {
    public static final String DATE_PATTERN = "yyyy-MM-dd";
    public static final String DATE_PATTERN_YMD = "yyyyMMdd";
    public static final String DATE_PATTERN_YMD_HM = "yyyy-MM-dd HH:mm";
    public static final String DATE_TIME_PATTERN = "yyyy-MM-dd HH:mm:ss";


    public static void main(String[] args) {
        Long createTime = 1650937800L;
        String dateStr = timeStamptoDateStr(createTime, null);
        log.info("=======dateStr:{} ", dateStr);
    }

    /**
     * timeStampDateStr 时间戳转日期字符
     *
     * @param timeStamp timeStamp
     * @param pattern   pattern
     * @return 日期格式字符
     */
    public static String timeStamptoDateStr(Long timeStamp, String pattern) {
        if (timeStamp == null) {
            return null;
        }
        if (StringUtils.isEmpty(pattern)) {
            pattern = DateTimeUtil.DATE_TIME_PATTERN;
        }
        SimpleDateFormat sdf = new SimpleDateFormat(pattern);

        // 时间戳分为10位数到秒级时间戳、13位到毫秒级时间戳，如果转换到了1970年，是因为需要的13位时间戳却用10位时间戳传参
        if (String.valueOf(timeStamp).length() == 10) {
            return sdf.format(timeStamp * 1000);
        }
        return sdf.format(timeStamp);
    }

    /**
     * timeStampToDate 时间戳转 Date
     *
     * @param timeStamp timeStamp
     * @return Date
     */
    public static Date timeStampToDate(long timeStamp) {
        String dateStr = timeStamptoDateStr(timeStamp, null);
        if (StringUtils.isEmpty(dateStr)) {
            return null;
        }
        SimpleDateFormat sdf = new SimpleDateFormat(DateTimeUtil.DATE_TIME_PATTERN);
        try {
            return sdf.parse(dateStr);
        } catch (ParseException e) {
            log.error("===timeStampToDate RuntimeException:{}", e);
            return null;
        }
    }

}