【Java】Java8日期处理实践

Java8日期处理实践

Java8日期API简介

Java 8 推出了全新的日期时间API，在教程中我们将通过一些简单的实例来学习如何使用新API。新API基于ISO标准日历系统，java.time包下的所有类都是不可变类型而且线程安全。

示例代码

package util;

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

public class TimeFormat {
    // 获取今天的日期
    public static void getTodayDate() {
        LocalDate today = LocalDate.now();
        System.out.println("今天的日期：" + today);
    }

    // 获取今天的年、月、日信息
    public static void getYearMonthDay() {
        LocalDate today = LocalDate.now();
        int year = today.getYear();
        int month = today.getMonthValue();
        int day = today.getDayOfMonth();
        System.out.println("年：" + year + ",月：" + month + ",日：" + day);
    }

    // 处理特定日期
    public static void reBuildDate() {
        LocalDate date = LocalDate.of(2020, 2, 6);
        System.out.println("自定义日期：" + date);
    }

    // 判断两个日期是否相等
    public static void judgeEqual() {
        LocalDate date1 = LocalDate.now();
        LocalDate date2 = LocalDate.of(2020, 1, 11);
        if (date1.equals(date2)) {
            System.out.println("时间相等");
        } else {
            System.out.println("时间不相等");
        }
    }

    // 检查像日期这种周期性事件
    public static void judgeEvent() {
        LocalDate date1 = LocalDate.now();
        LocalDate date2 = LocalDate.of(2019, 2, 11);
        MonthDay birthday = MonthDay.of(date2.getMonth(), date1.getDayOfMonth());
        MonthDay currentMonthDay = MonthDay.from(date1);
        if (currentMonthDay.equals(birthday)) {
            System.out.println("是你的生日");
        } else {
            System.out.println("你的生日还没到");
        }
    }

    // 获取当前时间
    public static void getTime() {
        LocalTime time = LocalTime.now();
        System.out.println("获取当前的时间，不含有日期：" + time);
    }

    // 获取当前时间2
    public static void getTime2() {
        LocalTime time = LocalTime.now();
        LocalTime newTime = time.plusHours(3);
        System.out.println("三个小时后的时间：" + newTime);
    }

    // 计算一周后的日期
    public static void getTimeAfterWeek() {
        LocalDate today = LocalDate.now();
        System.out.println("今天的日期为：" + today);
        LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS);
        System.out.println("一周后的日期为：" + nextWeek);
    }

    // 计算一年前或一年后的日期
    public static void getTimeAfterYear() {
        LocalDate today = LocalDate.now();
        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);
    }

    // Clock时钟类
    public static void clockClass() {
        Clock clock = Clock.systemUTC();
        System.out.println("Clock:" + clock.millis());

        Clock defaultClock = Clock.systemDefaultZone();
        System.out.println("Clock: " + defaultClock.millis());
    }

    // 判断一个日期早于还是晚于一个日期
    public static void judgeBefororAfter() {
        LocalDate today = LocalDate.now();
        LocalDate tomorrow = LocalDate.of(2020, 2, 12);
        if (tomorrow.isAfter(today)) {
            System.out.println("之后的日期：" + tomorrow);
        }
        LocalDate yesterday = today.minus(1, ChronoUnit.DAYS);
        if (yesterday.isBefore(today)) {
            System.out.println("之前的日期：" + yesterday);
        }
    }

    // 处理时区
    public static void getTimeZone() {
        ZoneId america = ZoneId.of("America/New_York");
        LocalDateTime localDateTime = LocalDateTime.now();
        ZonedDateTime dateTimeInNewYork = ZonedDateTime.of(localDateTime, america);
        System.out.println("Current date and time in a particular timezone:" + dateTimeInNewYork);
    }

    // 表示信用卡到期之类的方法
    public static void creditCardExpiry() {
        YearMonth currentYearMonth = YearMonth.now();
        System.out.printf("Days in month year %s: %d%n", currentYearMonth, currentYearMonth.lengthOfMonth());
        YearMonth creditCardExpiry = YearMonth.of(2020, Month.FEBRUARY);
        System.out.printf("Your credit card expirds on %s %n", creditCardExpiry);
    }

    // 检查闰年
    public static void judgeIsLeapYear() {
        LocalDate today = LocalDate.now();
        if (today.isLeapYear()) {
            System.out.println("This is a Leap Year");
        } else {
            System.out.println("This is not a Leap Year");
        }
    }

    // 计算两个日期之间的天数和月数
    public static void getDaysAndMonthsBetweenTwoDate() {
        LocalDate today = LocalDate.now();
        LocalDate java8Release = LocalDate.of(2020, 2, 13);
        Period periodToNextJavaRelease = Period.between(today, java8Release);
        System.out.println("Months left between today and java 8 Release:" + periodToNextJavaRelease.getMonths());
    }

    // 获取当前的时间戳
    public static void getTimeStamp() {
        Instant timeStamp = Instant.now();
        System.out.println("What is the value of this instant " + timeStamp.toEpochMilli());
    }

    // 如何使用预定义的格式化工具解析或格式化日期
    public static void formatDate() {
        String dayAfterTomorrow = "20200211";
        LocalDate formatted = LocalDate.parse(dayAfterTomorrow, DateTimeFormatter.BASIC_ISO_DATE);
        System.out.println(dayAfterTomorrow + " 格式化之后的日期为：" + formatted);
    }

    // 字符串互转日期类型
    public static void string2date() {
        LocalDateTime date = LocalDateTime.now();
        DateTimeFormatter format1 = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        // 日期转字符串
        String str = date.format(format1);
        System.out.println("日期转字符串：" + str);
        DateTimeFormatter format2 = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        // 字符串转日期
        LocalDate date2 = LocalDate.parse(str, format2);
        System.out.println("日期类型：" + date2);
    }

    public static void main(String[] args) {
        getTimeStamp();
        getTimeZone();
        getYearMonthDay();
        getDaysAndMonthsBetweenTwoDate();
        getTime();
        getTime2();
        judgeBefororAfter();
        judgeEqual();
        judgeEvent();
        judgeIsLeapYear();
    }
}