java8日期类常用方法使用总结

java8已经推出了五六年时间了，项目中也经常用到它的一些特性，但是在日期使用方面，没有进行过较为全面的梳理，临近年关，今日得空整理出来，一来备忘而来分享。
日期时间方面的常用类有三个LocalDate、LocalTime 、LocalDateTime ，最为常用当属LocalDateTime
以上三种使用方式大同小异，着重记录下LocalDateTime 的使用

import org.junit.Test;

import java.util.Date;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;

public class LocalDateDemo {

    @Test
    public void testLocalDate() {
        LocalDate today = LocalDate.now();
        System.out.println("今天的日期:"+ today);

        int year = today.getYear();
        int month = today.getMonthValue();
        int day = today.getDayOfMonth();
        System.out.println("year:"+year);
        System.out.println("month:"+month);
        System.out.println("day:"+day);

        LocalDate previousYear = today.minus(1, ChronoUnit.YEARS);
        System.out.println("一年前的日期 : " + previousYear);
        LocalDate nextYear = today.plus(1, ChronoUnit.YEARS);
        System.out.println("一年后的日期:"+nextYear);

        LocalDate previousWeek = today.minus(1, ChronoUnit.WEEKS);
        System.out.println("一周前的日期为:"+previousWeek);
        LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS);
        System.out.println("一周后的日期为:"+nextWeek);

        LocalDate date = LocalDate.of(2018,2,6);
        System.out.println("自定义日期:"+date);

        System.out.println("日期比较:"+today.equals(date));

        System.out.println("previousWeek早于nextWeek:"+previousWeek.isBefore(nextWeek));
    }

    @Test
    public void testLocalTime() {
        LocalTime time = LocalTime.now();
        System.out.println("获取当前的时间,不含有日期:"+time);

        LocalTime previousTime = time.minusHours(3);
        System.out.println("三个小时前的时间为:"+previousTime);
        LocalTime newTime = time.plusHours(3);
        System.out.println("三个小时后的时间为:"+newTime);
        //分秒同理~

    }

    @Test
    public void testLocalDateTime() {
        LocalDateTime now = LocalDateTime.now();
        System.out.println("获取当前的时间,含有日期:"+now);

        //自定义时间，可精确到纳秒
        LocalDateTime time = LocalDateTime.of(2020,01,21,9,44, 37, 20111111);
        System.out.println("自定义时间:"+time);
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        String formatStr = time.format(formatter);
        System.out.println("时间转格式化字符串:"+ formatStr);
        LocalDateTime parse = LocalDateTime.parse(formatStr, formatter);
        System.out.println("格式化字符串转时间:"+ parse);

		//加减年月日时分秒
        LocalDateTime previousTime = time.minusHours(3);
        System.out.println("三个小时前的时间为:"+previousTime);
        LocalDateTime newTime = time.plusHours(3);
        System.out.println("三个小时后的时间为:"+newTime);
        System.out.println("修该年:"+LocalDate.now().withYear(2019));
        System.out.println("判断当前是否闰年:"+LocalDate.now().isLeapYear());
        //分秒同理~

        //获取间隔时间
        Duration duration = Duration.between(previousTime,newTime);
        System.out.println("相距日："+duration.toDays());
        System.out.println("相距时："+duration.toHours());
        System.out.println("相距分："+duration.toMinutes());
        System.out.println("相距秒："+duration.toMillis());

        //LocalDateTime与Date之间互转
        Date date = Date.from(newTime.atZone(ZoneId.systemDefault()).toInstant());
        LocalDateTime dateTime = LocalDateTime.ofInstant(date.toInstant(),ZoneId.systemDefault());
        System.out.println("LocalDateTime转Date:" + date);
        System.out.println("Date转LocalDateTime:" + dateTime);

        //时间戳
        System.out.println("时间戳（秒）："+LocalDateTime.now().toInstant(ZoneOffset.of("+8")).getEpochSecond());
        System.out.println("时间戳（秒）："+Instant.now().getEpochSecond());
        System.out.println("时间戳（毫秒）："+LocalDateTime.now().toInstant(ZoneOffset.of("+8")).toEpochMilli());
        System.out.println("时间戳（毫秒）："+Instant.now().toEpochMilli());
    }

}