「JDK8」LocalDateTime和LocalDate等API

LocalDate API

import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;
import java.time.temporal.TemporalAdjusters;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class LocalDateTest {

    static DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");

    public static void main(String[] args) {
        //获得当前时间
        LocalDate today = LocalDate.now();

        //获取年份
        int year = today.getYear(); //2022

        //获取月份
        int month = today.getMonthValue(); //1~12

        //获取日期
        int day = today.getDayOfMonth(); //1~31

        //一年中的第几天
        int dayOfYear = today.getDayOfYear();

        //DayOfWeek是代表一周中7天的枚举 - 星期一，星期二，星期三，星期四，星期五，星期六和星期日
        DayOfWeek week = today.getDayOfWeek();
        int weekValue = week.getValue(); //星期三, 值为3

        //获取当前时间前/后X天的日期
        //获取前一天的日期
        LocalDate data = today.plusDays(-1);
        //获取后一天的日期
        LocalDate data1 = today.plusDays(+1);

        //获取本周周一的日期
        LocalDate weekOfFirstDay = today.with(DayOfWeek.MONDAY);

        //获取本月第一天的日期
        LocalDate monthOfFirstDay = today.with(TemporalAdjusters.firstDayOfMonth());

        //获取月份总天数
        int totalDays = today.withMonth(today.getMonthValue()).lengthOfMonth();

        //获取年份的第一天
        LocalDate firstDayOfYear = today.with(TemporalAdjusters.firstDayOfYear());

        //是否闰年
        boolean leapYear = today.isLeapYear();
        System.out.println(leapYear);

        //一天的开始时间
        LocalDateTime localDateTime = today.atStartOfDay();

        //日期结合时间
        LocalDateTime localDateTime1 = today.atTime(LocalTime.parse("12:10:20"));
        System.out.println(localDateTime1);
        LocalDateTime localDateTime2 = today.atTime(8, 3);
        System.out.println(localDateTime2);

        //指定年份, 这里表示2010年
        LocalDate localDate3 = today.withYear(2010);
        System.out.println(localDate3);

        //指定月份, 这里表示12月份
        LocalDate localDate4 = today.withMonth(12);
        System.out.println(localDate4);
        LocalDate localDate5 = today.with(ChronoField.MONTH_OF_YEAR, 2);
        System.out.println(localDate5);

        //指定日期, 这里表示25号
        LocalDate localDate = today.withDayOfMonth(25);
        System.out.println(localDate);

        //自定义年月日的LocalDate
        LocalDate localDate6 = LocalDate.of(2022, 12, 1);
        System.out.println(localDate6);
        
        //String转LocalDate
        LocalDate date = LocalDate.parse("2020-01-01");
        LocalDate date1 = LocalDate.parse("2020-01-01", dateTimeFormatter);

        //LocalDate转String
        String dateStr = today.format(dateTimeFormatter);
        System.out.println(dateStr);

        //获取两个时间间隔中的每一天
        List<String> list = new ArrayList();
        LocalDate startDate = LocalDate.parse("2020-01-01");
        LocalDate endDate = LocalDate.parse("2020-01-10");
        long distance = ChronoUnit.DAYS.between(startDate, endDate);  //传入开始时间和结束时间
        if (distance > 0) {
            Stream.iterate(startDate, d -> d.plusDays(1)).limit(distance + 1).forEach(f -> list.add(f.toString()));
        }
        System.out.println(list);

        //比较两个日期的大小
        //判断localDate1是否和localDate2相等，返回布尔值
        LocalDate localDate1 = LocalDate.parse("2020-01-01");
        LocalDate localDate2 = LocalDate.parse("2020-01-01");
        boolean equal = localDate1.isEqual(localDate2);
        System.out.println(equal);
        //判断localDate1是否在localDate2之前，返回布尔值
        boolean before = localDate1.isBefore(localDate2);
        System.out.println(before);
        //判断localDate1是否在localDate2之后，返回布尔值
        boolean after = localDate1.isAfter(localDate2);
        System.out.println(after);

        //两个时间间隔天数
        LocalDate date4 = LocalDate.of(2022, 4, 30);
        LocalDate date5 = LocalDate.of(2022, 4, 21);
        int countdown = Math.toIntExact(date4.toEpochDay() - date5.toEpochDay());
        System.out.println(countdown); //date4 > date5为正数
    }
}

LocalDateTime API

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class LocalDateTimeTest {

    static DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

    public static void main(String[] args) {
        //获取当前时间
        LocalDateTime today = LocalDateTime.now();
        //年
        int year = today.getYear();
        //月
        int month = today.getMonthValue();
        //日
        int day = today.getDayOfMonth();
        //时
        int hour = today.getHour();
        //分
        int minute = today.getMinute();
        //秒
        int second = today.getSecond();

        //LocalDateTime和String相互转换
        //LocalDateTime转String
        String formatResult = dateTimeFormatter.format(today);
        //String转LocalDateTime
        LocalDateTime parseDateTime = LocalDateTime.parse("2022-06-22 10:12:20", dateTimeFormatter);
    }
}

LocalTime API

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;

public class LocalTimeTest {

    public static void main(String[] args) {
        //获取当前的时间, 时分秒
        LocalTime today = LocalTime.now();
        //时
        int hour = today.getHour();
        //分
        int minute = today.getMinute();
        //秒
        int second = today.getSecond();
        //纳秒
        int nano = today.getNano();

        //获取指定Field的值
        today.getLong(ChronoField.HOUR_OF_DAY);

        //截断
        //ChronoUnit.HOURS 14:54:12.317 -> 14:00
        //ChronoUnit.MINUTES 14:54:12.317 -> 14:54
        //ChronoUnit.SECONDS 14:54:12.317 -> 14:54:12
        LocalTime localTime = today.truncatedTo(ChronoUnit.SECONDS);
        System.out.println(localTime);

        //将时间LocalTime结合到LocalDate中
        LocalDateTime localDateTime = today.atDate(LocalDate.parse("2022-06-20"));
        System.out.println(localDateTime);
    }
}