从LocalDateTime到Instant详解Java 8+中时间类型的使用

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

public class LocalTimeDemo {
    public static void main(String[] args) {
        // 1. 获取当前时间
        LocalDate today = LocalDate.now();
        LocalTime nowTime = LocalTime.now();
        LocalDateTime now = LocalDateTime.now();

        // 2. 手动创建时间
        LocalDate birthDay = LocalDate.of(2000, 1, 1);
        LocalDateTime meeting = LocalDateTime.of(2025, 12, 25, 14, 30);

        // 3. 常用操作：加减时间（不可变，返回新对象）
        LocalDate nextWeek = today.plusWeeks(1);
        LocalDateTime beforeHour = now.minusHours(1);

        System.out.println("当前日期：" + today);
        System.out.println("会议时间：" + meeting);
    }
}

import java.time.OffsetDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;

public class ZoneTimeDemo {
    public static void main(String[] args) {
        // 1. 当前带偏移量的时间
        OffsetDateTime offsetNow = OffsetDateTime.now();

        // 2. 指定时区创建时间
        ZonedDateTime shanghaiTime = ZonedDateTime.now(ZoneId.of("Asia/Shanghai"));
        ZonedDateTime newYorkTime = ZonedDateTime.now(ZoneId.of("America/New_York"));

        System.out.println("上海时间：" + shanghaiTime);
        System.out.println("纽约时间：" + newYorkTime);
    }
}

import java.time.Instant;

public class InstantDemo {
    public static void main(String[] args) {
        // 1. 获取当前时间戳
        Instant now = Instant.now();

        // 2. 时间戳转秒/毫秒（兼容旧系统）
        long second = now.getEpochSecond();
        long milli = now.toEpochMilli();

        // 3. 手动创建
        Instant instant = Instant.ofEpochMilli(System.currentTimeMillis());

        System.out.println("当前UTC时间：" + now);
        System.out.println("时间戳（毫秒）：" + milli);
    }
}

import java.time.Duration;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.Period;

public class TimeGapDemo {
    public static void main(String[] args) {
        // 1. 计算日期间隔（生日天数）
        LocalDate today = LocalDate.now();
        LocalDate birthDay = LocalDate.of(2000, 1, 1);
        Period period = Period.between(birthDay, today);
        System.out.println("年龄：" + period.getYears() + "岁");

        // 2. 计算时间间隔（会议时长）
        LocalDateTime start = LocalDateTime.of(2025, 12, 25, 14, 0);
        LocalDateTime end = LocalDateTime.of(2025, 12, 25, 16, 30);
        Duration duration = Duration.between(start, end);
        System.out.println("会议时长：" + duration.toHours() + "小时");
    }
}

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

public class FormatDemo {
    public static void main(String[] args) {
        // 定义格式化器
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        LocalDateTime now = LocalDateTime.now();

        // 时间 → 字符串
        String formatTime = now.format(formatter);

        // 字符串 → 时间
        LocalDateTime parseTime = LocalDateTime.parse("2025-12-25 14:30:00", formatter);

        System.out.println("格式化后：" + formatTime);
    }
}

// LocalDateTime → Instant（带时区）
LocalDateTime local = LocalDateTime.now();
Instant instant = local.atZone(ZoneId.systemDefault()).toInstant();

// Instant → LocalDateTime
LocalDateTime localTime = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());