Java8 日期时间API

//LocalDateTime 转 字符串
String str = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss").format(LocalDateTime.now());
//字符串 转 LocalDateTime 
 LocalDateTime localDateTime = LocalDateTime.parse("2019-06-26 19:00:00",
                                          DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));

// Date 转 LocalDateTime 与 LocalDate
Date date = new Date();
Instant instant = date.toInstant();
ZoneId zoneId = ZoneId.systemDefault();
LocalDateTime localDateTime = instant.atZone(zoneId).toLocalDateTime();
LocalDate localDate = instant.atZone(zoneId).toLocalDate();
//也可以使用LocalDateTime的FactoryInput（）方法使用系统的默认时区
LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), zoneId);
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// LocalDateTime 转换成 Date
ZoneId zoneId = ZoneId.systemDefault();
ZonedDateTime zdt = localDateTime.atZone(zoneId);
Date date = Date.from(zdt.toInstant());
// LocalDate 转换成 Date
ZoneId zoneId = ZoneId.systemDefault();
ZonedDateTime zdt = localDate.atStartOfDay(zoneId);
Date date = Date.from(zdt.toInstant());

LocalDateTime now = LocalDateTime.now();
LocalDate localDate = now.toLocalDate();

String time1 = "2019-06-26 19:00:00";
DateTimeFormatter dtf2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime localDateTime = LocalDateTime.parse(time1, dtf2);
System.out.println(localDateTime.isBefore(LocalDateTime.now()));//如果你的时间在当前时间之前，那么就是true
System.out.println(localDateTime.isAfter(LocalDateTime.now()));//反之是否在当前时间之后就是false

1.Period
2.Duration
3.ChronoUnit

主要是Period类方法getYears（），getMonths（）和getDays（）来计算.

import java.time.LocalDate;
import java.time.Month;
import java.time.Period;
public class Test {
    public static void main(String[] args) {
        LocalDate today = LocalDate.now();
        System.out.println("Today : " + today);
        LocalDate birthDate = LocalDate.of(1993, Month.OCTOBER, 19);
        System.out.println("BirthDate : " + birthDate);
        Period p = Period.between(birthDate, today);
        System.out.printf("年龄 : %d 年 %d 月 %d 日", p.getYears(), p.getMonths(), p.getDays());
    }
}

Today : 2017-06-16
BirthDate : 1993-10-19
年龄 : 23 年 7 月 28 日

LocalDateTime now = LocalDateTime.now();
Duration duration = Duration.between(now,now);
    long days = duration.toDays(); //相差的天数
    long hours = duration.toHours();//相差的小时数
    long minutes = duration.toMinutes();//相差的分钟数
    long millis = duration.toMillis();//相差毫秒数
    long nanos = duration.toNanos();//相差的纳秒数
    System.out.println(millis);

public static void main(String[] args) {
    String str1 = "2019-11-18 12:10:01";
    String str2 = "2019-11-18 14:12:09";
    LocalDateTime date1 = LocalDateTime.parse(str1, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
    LocalDateTime date2 = LocalDateTime.parse(str2, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));

    Duration duration = Duration.between(date1, date2);
    System.out.println(duration);
    long days = duration.toDays(); //相差的天数
    long hours = duration.toHours();//相差的小时数
    long minutes = duration.toMinutes();//相差的分钟数
    long seconds = duration.toMillis() / 1000;//相差秒数
    System.out.println(String.format("%s小时%s分%s秒", hours, minutes - hours * 60, seconds - minutes * 60));

    System.out.println("-----------------------------------------");
    long d = ChronoUnit.DAYS.between(date1, date2);  //相差的天数
    long h = ChronoUnit.HOURS.between(date1, date2); //相差的小时数
    long m = ChronoUnit.MINUTES.between(date1, date2); //相差的分钟数
    long s = ChronoUnit.SECONDS.between(date1, date2); //相差秒数
    System.out.println(String.format("%s小时%s分%s秒", h, m - h * 60, s - m * 60));
}

PT2H2M8S
2小时2分8秒
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2小时2分8秒

Process finished with exit code 0