Java之Date Time API (Java 8 新特性)

Java 8 – Date Time API

Java 8 comes with a much improved and much required change in the way date and time is handled.
The classes that represent the date and time concepts are present in the java.time package.

The important classes in this package are:

• java.time.Period: This class represents the date part of the datetime. It represents the date part in terms of days, months and years. for example 1 year, 2 months and 5 days
• java.time.Duration: This class represents the time part of the datetime. It represents the time part in terms of seconds and nanoseconds. for example ’29 seconds’
• java.time.Instant: This represents a particular instant in the timeline. It stores the number of seconds through epoch time and also has another field that stores the nanoseconds
• java.time.LocalDate: This stores the date part of date-time in terms of years-months-days. It does not store the TimeZone. The class is immutable.
• java.time.LocalTime: This class stores the time part of date time without any TimeZone info.
• java.time.LocalDateTime: This class stores the LocalDate and LocalTime but no TimeZone
• java.time.ZonedDateTime: This class stores the LocalDateTime and the TimeZone info as a ZoneOffset object. The class has access to ZoneRules which can be used to convert to local time
• java.time.ZoneOffset:This stores the time zone offset from UTC. The zone rules are stored in ZoneId.
• java.time.OffsetDateTime:This stores the local datetime with the offset. This class does not have information about Zone Rules.

package java8.datetime;

import java.time.LocalDate;
import java.time.LocalTime;

/**
 * Java 8 – Date Time API
 * LocalTime：当前时间
 * LocalDate：当前日期
 */
public class LocalTimeDemo3 {
    public static void main(String[] args) {
        LocalTime localTime = LocalTime.now();
        System.out.println("当前时间：" + localTime);

        LocalDate localDate = LocalDate.now();
        System.out.println("当前日期：" + localDate);
    }
}

LocalDateTime

package java8.datetime;

import java.time.DayOfWeek;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.temporal.ChronoField;

/**
 * Java 8 – Date Time API
 * LocalDateTime
 * url：http://www.studytrails.com/java/java8/java8_date_and_time/
 */
public class LocalDateTimeDemo2 {
    public static void main(String[] args) {
//        create a LocalDateTime
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println("新建LocalDateTime对象：" + localDateTime); // prints 2018-02-12T15:08:44.116

//        Convert LocalDateTime to datetime in particular zone
        System.out.println("指定时区：" + localDateTime.atZone(ZoneId.of("America/New_York")));

//        Get the day of week from DateTime
        System.out.println("星期几：" + DayOfWeek.from(localDateTime)); // prints SUNDAY.

//        Get the day of year from DateTime
        System.out.println("当年第几天：" + localDateTime.get(ChronoField.DAY_OF_YEAR)); // prints 43
//        The other fields that can be returned are MINUTE_OF_HOUR, MINUTE_OF_DAY, HOUR_OF_AMPM,
//        HOUR_OF_DAY, AMPM_OF_DAY, DAY_OF_WEEK, DAY_OF_MONTH, DAY_OF_YEAR, MONTH_OF_YEAR,
//        YEAR, OFFSET_SECONDS (offset from UTC).

//       获得当前日期
        System.out.println("当前日期：" + localDateTime.toLocalDate());
        // prints 2014-09-29

        // 获取当前时间
        System.out.println("当前时间：" + localDateTime.toLocalTime());
        // prints 22:26:30.146

//        Create a LocalDateTime from year, month, day, hour, min
        System.out.println("实例化LocalDateTime by Int：" + LocalDateTime.of(2014, 10, 1, 10, 0));
        // prints 2014-10-01T10:00

//        Create LocalDateTime by parsing a string
        LocalDateTime parsedLocalDateTime = LocalDateTime.parse("2014-01-01T11:00");
        System.out.println("实例化LocalDateTime by String：" + parsedLocalDateTime);

        System.out.println("当前小时点：" + localDateTime.getHour());


    }
}

Instant

package java8.datetime;

import java.time.Instant;
import java.time.temporal.ChronoUnit;

/**
 * Java 8 – Date Time API
 * Instant
 * url：http://www.studytrails.com/java/java8/java8_date_and_time/
 */
public class InstantDemo1 {
    public static void main(String[] args) {
        //Creating a local date
        Instant now = Instant.now();
        //2018-02-12T06:29:01.493Z
        System.out.println("当前时间：" + now);

//      The epoch seconds is the number of seconds since 1970-01-01T00:00:00Z
        System.out.println("当前秒数：" + now.getEpochSecond());

//      调整时间
//      the plus function allows adding time intervals.
//      The time intervals can be NANOS, MICROS, MILLIS, SECONDS, MINUTES, HOURS, HALF_DAYS, DAYS
        Instant tomorrow = now.plus(2, ChronoUnit.DAYS);
        System.out.println("明天时间：" + tomorrow);
//        The minus function allows subtracting time from an instant.
        Instant yesterday = now.minus(1, ChronoUnit.DAYS);
        System.out.println("昨天时间：" + yesterday);

//      The compare function can be used to compare two dates.
//      It returns -1 if the date that is passed is after , 1 if it is before
        System.out.println("今天和明天比较：" + now.compareTo(tomorrow));// prints -1

//        check if one instant is after another
        System.out.println("今天是否在昨天后面：" + now.isAfter(yesterday));// prints true

    }
}