LocalDateTime工具类

 常用对象

 ZoneId: 时区ID，用来确定Instant和LocalDateTime互相转换的规则
 Instant: 用来表示时间线上的一个点（瞬时）
 LocalDate: 表示没有时区的日期, LocalDate是不可变并且线程安全的
 LocalTime: 表示没有时区的时间, LocalTime是不可变并且线程安全的
 LocalDateTime: 表示没有时区的日期时间, LocalDateTime是不可变并且线程安全的

工具类

import java.text.DateFormat;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.util.Date;

/* 
 * @creator wangli66
 * @create-time 20:05 2019/12/19
 **/
public class DateTimeUtils {
    // 时区
    private static String zoneId = "Asia/Shanghai";
    // 日期格式
    private static String dateFormat = "yyyy-MM-dd HH:mm:ss";

    /*
     * @Description: 传日期字符串返回日期
     * @param: [dateTime]
     * @return: java.time.LocalDateTime
     * @Date: 2019/12/19
     */
    public static LocalDateTime stringToDate(String dateTime) {
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(dateFormat);
        LocalDateTime localDateTime = LocalDateTime.parse(dateTime, dateTimeFormatter);
        return localDateTime;
    }

    /*
     * @Description: 传日期格式化为字符串
     * @param: [localDateTime]
     * @return: java.lang.String
     * @Date: 2019/12/19
     */
    public static String dateToString(LocalDateTime localDateTime) {
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern(dateFormat);
        String format = dateTimeFormatter.format(localDateTime);
        return format;
    }

    /*
     * @Description: date转换为localdatetime
     * @param: [date]
     * @return: java.time.LocalDateTime
     * @Date: 2019/12/20
     */
    public static LocalDateTime dateToLocalDateTime(Date date) {
        Instant instant = date.toInstant();
        ZoneId zoneId = ZoneId.systemDefault();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zoneId);
        return localDateTime;
    }

    /*
     * @Description: localDateTime转换为Date
     * @param: [localDateTime]
     * @return: java.util.Date
     * @Date: 2019/12/20
     */
    public static Date localDateTimeToDate(LocalDateTime localDateTime) {
        Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
        return Date.from(instant);
    }

    /*
     * @Description: 毫秒数转换为localdatetime
     * @param: [time]
     * @return: java.time.LocalDateTime
     * @Date: 2019/12/20
     */
    public static LocalDateTime longToLocalDateTime(long time) {
        return LocalDateTime.ofInstant(Instant.ofEpochMilli(time), ZoneId.systemDefault());
    }

    /*
     * @Description: localdatetime转换为毫秒数
     * @param: [ldt]
     * @return: long
     * @Date: 2019/12/20
     */
    public static long localDateTimeToLong(LocalDateTime ldt) {
        return ldt.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
    }

    public static void main(String[] args) {
        LocalDateTime localDateTime = DateTimeUtils.stringToDate("2019-12-19 20:23:54");
        System.out.println("字符串转换时间：" + localDateTime);
        String date = DateTimeUtils.dateToString(LocalDateTime.now());
        System.out.println("时间转换字符串：" + date);
        LocalDateTime localDateTime1 = DateTimeUtils.dateToLocalDateTime(new Date());
        System.out.println("Date转换LocalDateTime：" + localDateTime1);
        Date date1 = DateTimeUtils.localDateTimeToDate(LocalDateTime.now());
        System.out.println("LocalDateTime转换Date：" + date1);
        LocalDateTime localDateTime2 = DateTimeUtils.longToLocalDateTime(System.currentTimeMillis());
        System.out.println("毫秒转换LocalDateTime：" + localDateTime2);
        long mills = DateTimeUtils.localDateTimeToLong(LocalDateTime.now());
        System.out.println("LocalDateTime转换毫秒：" + mills);
    }
}

测试结果