Java8中的日期时间类

 测试类：

import java.time.*;
import java.time.format.DateTimeFormatter;

public class App 
{
    public static void main( String[] args )
    {

        LocalDateTime time = LocalDateTime.now();
        System.out.println(time.toString()); //输出日期时间：2019-05-04T18:27:55.240
        System.out.println(time.toLocalDate());  //输出日期：2019-05-04
        System.out.println(time.toLocalTime());  //输出时间：18:27:55.240
        System.out.println(time.getDayOfMonth()); //输出当前日期月份的第几天：4
        System.out.println(time.getDayOfWeek()); //输出档期日期周几：SATURDAY
        System.out.println(time.getDayOfYear()); //当前日期在该年属于第几天：124
        System.out.println(time.getHour());  //输出：18
        System.out.println(time.getMinute()); //输出：27
        System.out.println(time.getSecond()); //输出：55
        System.out.println(time.getMonthValue()); //输出：5
        System.out.println(time.getMonth());  //输出：MAY
        System.out.println("==============================================");

        //格式化输出：
        DateTimeFormatter format = DateTimeFormatter.ofPattern("YYYY-MM-dd HH:mm:ss");
        System.out.println(time.format(format));  //输出：2019-05-04 18:27:55

        //构造时间
        LocalDateTime startTime = LocalDateTime.of(2019,05,04,17,59);
        System.out.println(startTime.format(format));  //输出：2019-05-04 17:59:00
        LocalDateTime endTime = LocalDateTime.of(LocalDate.now(), LocalTime.of(0,0,0));
        System.out.println(endTime.format(format));  //输出：2019-05-04 00:00:00

        //时间比较
        System.out.println(time.isAfter(startTime));  //输出：true
        System.out.println(time.isBefore(endTime));  //输出：false

        //时间运算
        System.out.println(time.plusDays(-1).format(format)); //输出：2019-05-03 18:27:55
        System.out.println(time.plusDays(1).format(format));  //输出：2019-05-05 18:27:55
        System.out.println(time.plusMonths(-1).format(format));  //输出：2019-04-04 18:27:55
        System.out.println(time.plusMonths(1).format(format));  //输出：2019-06-04 18:27:55
        System.out.println(time.getHour());  //输出：18
        System.out.println(time.withHour(1).format(format));  //输出：2019-05-04 01:27:55


        //获取毫秒数时间戳
        long milliSec = time.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        System.out.println(milliSec);  //输出：1556965675240
        //获取秒数时间戳
        long sec = time.atZone(ZoneId.systemDefault()).toInstant().getEpochSecond();
        System.out.println(sec);  //输出：1556965675
        //时间戳转换为时间
        LocalDateTime time2 =LocalDateTime.ofInstant(Instant.ofEpochMilli(milliSec),ZoneId.systemDefault());
        System.out.println(time2.format(format));  //输出：2019-05-04 18:27:55
        LocalDateTime time3 = LocalDateTime.ofInstant(Instant.ofEpochSecond(sec),ZoneId.systemDefault());
        System.out.println(time3.format(format));  //输出：2019-05-04 18:27:55

    }
}

输出结果：

2019-05-04T18:27:55.240
2019-05-04
18:27:55.240
4
SATURDAY
124
18
27
55
5
MAY
==============================================
2019-05-04 18:27:55
2019-05-04 17:59:00
2019-05-04 00:00:00
true
false
2019-05-03 18:27:55
2019-05-05 18:27:55
2019-04-04 18:27:55
2019-06-04 18:27:55
18
2019-05-04 01:27:55
1556965675240
1556965675
2019-05-04 18:27:55
2019-05-04 18:27:55