Java时间戳转换完整教程

// 传统方式 - 毫秒级时间戳
long timestampMs = System.currentTimeMillis();
System.out.println(timestampMs);  // 1735660800000L

// 秒级时间戳
long timestampSec = System.currentTimeMillis() / 1000;
System.out.println(timestampSec);  // 1735660800

// Java 8+ 方式
import java.time.Instant;

Instant now = Instant.now();
long epochSec = now.getEpochSecond();      // 秒级
long epochMilli = now.toEpochMilli();       // 毫秒级
System.out.println("秒级: " + epochSec);
System.out.println("毫秒: " + epochMilli);

// Java 8+ 方式（推荐）
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

long timestamp = 1735660800L;

// 转为Instant
Instant instant = Instant.ofEpochSecond(timestamp);

// 转为本地时间
LocalDateTime localDateTime = LocalDateTime.ofInstant(
    instant, 
    ZoneId.systemDefault()
);

// 格式化输出
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
System.out.println(localDateTime.format(formatter));  // 2025-01-01 00:00:00

// 转为指定时区时间
ZonedDateTime zonedDateTime = instant.atZone(ZoneId.of("Asia/Shanghai"));
System.out.println(zonedDateTime.format(formatter));

// 传统方式（Java 8之前）
import java.util.Date;
import java.text.SimpleDateFormat;

Date date = new Date(timestamp * 1000L);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println(sdf.format(date));

// LocalDateTime转时间戳
import java.time.LocalDateTime;
import java.time.ZoneId;

LocalDateTime dateTime = LocalDateTime.of(2025, 1, 1, 0, 0, 0);
long timestamp = dateTime.atZone(ZoneId.systemDefault()).toEpochSecond();
System.out.println(timestamp);  // 1735660800

// 解析日期字符串
import java.time.format.DateTimeFormatter;

String dateStr = "2025-01-01 00:00:00";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime parsed = LocalDateTime.parse(dateStr, formatter);
long ts = parsed.atZone(ZoneId.systemDefault()).toEpochSecond();

// ISO格式直接解析
import java.time.Instant;
Instant instant = Instant.parse("2025-01-01T00:00:00+08:00");
long ts2 = instant.getEpochSecond();

// 传统方式
import java.util.Date;
Date date = new Date();
long legacyTs = date.getTime() / 1000;

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

LocalDateTime dateTime = LocalDateTime.of(2025, 1, 1, 0, 0, 0);

// 预定义格式
System.out.println(dateTime.format(DateTimeFormatter.ISO_LOCAL_DATE));       // 2025-01-01
System.out.println(dateTime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME));  // 2025-01-01T00:00:00

// 自定义格式
DateTimeFormatter[] formatters = {
    DateTimeFormatter.ofPattern("yyyy-MM-dd"),
    DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss"),
    DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH时mm分ss秒"),
    DateTimeFormatter.ofPattern("EEE, MMM dd, yyyy"),
};

for (DateTimeFormatter fmt : formatters) {
    System.out.println(dateTime.format(fmt));
}

// 线程安全的格式化
// DateTimeFormatter是不可变的，可以安全地在多线程中使用
private static final DateTimeFormatter DATE_FORMATTER = 
    DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

import java.time.Instant;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

// 获取当前时间在不同时区的表示
Instant now = Instant.now();

// 转换为不同时区
ZoneId shanghai = ZoneId.of("Asia/Shanghai");
ZoneId newYork = ZoneId.of("America/New_York");
ZoneId london = ZoneId.of("Europe/London");
ZoneId utc = ZoneId.of("UTC");

ZonedDateTime shanghaiTime = now.atZone(shanghai);
ZonedDateTime newYorkTime = now.atZone(newYork);
ZonedDateTime londonTime = now.atZone(london);

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

System.out.println("上海: " + shanghaiTime.format(formatter));
System.out.println("纽约: " + newYorkTime.format(formatter));
System.out.println("伦敦: " + londonTime.format(formatter));

// 时区转换
ZonedDateTime converted = shanghaiTime.withZoneSameInstant(newYork);
System.out.println("上海转纽约: " + converted.format(formatter));

import java.time.LocalDateTime;
import java.time.temporal.ChronoUnit;
import java.time.Duration;
import java.time.Period;

LocalDateTime now = LocalDateTime.now();
LocalDateTime future = now.plusDays(7).plusHours(3).plusMinutes(30);

// 时间差计算
long daysBetween = ChronoUnit.DAYS.between(now, future);
long hoursBetween = ChronoUnit.HOURS.between(now, future);
long minutesBetween = ChronoUnit.MINUTES.between(now, future);

// 使用Duration
Duration duration = Duration.between(now, future);
System.out.println("相差分钟: " + duration.toMinutes());

// 使用Period
LocalDateTime date1 = LocalDateTime.of(2025, 1, 1, 0, 0);
LocalDateTime date2 = LocalDateTime.of(2025, 2, 15, 12, 30);
Period period = Period.between(date1.toLocalDate(), date2.toLocalDate());
System.out.println("相差: " + period.getMonths() + "月" + period.getDays() + "天");

// 时间比较
boolean isAfter = now.isAfter(future);  // false
boolean isBefore = now.isBefore(future);  // true
boolean isEqual = now.isEqual(future);  // false