Python工程师Java之路（f）Java时间API+时间类型转换

导入：java.time

• LocalDateTime：时间类型
• format.DateTimeFormatter：时间格式
• ZoneOffset：时区偏移量

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

public class Hello {
    public static void main(String[] args) {
    }
}

LocalDateTime

LocalDateTime now = LocalDateTime.now();
int year = now.getYear();
int month = now.getMonthValue();
int day = now.getDayOfMonth();
int hour = now.getHour();
int minute = now.getMinute();
int second = now.getSecond();
String weekday = now.getDayOfWeek().toString();
System.out.println(now);
System.out.println(year);
System.out.println(month);
System.out.println(day);
System.out.println(hour);
System.out.println(minute);
System.out.println(second);
System.out.println(weekday);

2021-03-15T17:32:02.715
2021
3
15
17
32
2
MONDAY

时间格式化

LocalDateTime now = LocalDateTime.now();
DateTimeFormatter ymd = DateTimeFormatter.ofPattern("yyyy年MM月dd日");
DateTimeFormatter hms = DateTimeFormatter.ofPattern("HH时mm分ss秒 SSS毫秒");
System.out.println(ymd.format(now));
System.out.println(hms.format(now));

2021年03月15日
17时32分02秒 715毫秒

返回当前系统时间距离1970-1-1 0:0:0的毫秒值

long millisecond = System.currentTimeMillis();

类型转换

// 毫秒数
long millis = System.currentTimeMillis();
System.out.println(millis);
// 毫秒数 -> LocalDateTime
LocalDateTime now = LocalDateTime.ofEpochSecond(
        millis / 1000, (int) ((millis % 1000) * 1e6), ZoneOffset.ofHours(8));
System.out.println(now);
// LocalDateTime -> String
DateTimeFormatter yMdMmsF = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS");
String yMdMmsStr = yMdMmsF.format(now);
System.out.println(yMdMmsStr);
// String -> LocalDateTime
LocalDateTime localDateTime = LocalDateTime.parse(yMdMmsStr, yMdMmsF);
System.out.println(localDateTime);
// LocalDateTime -> 毫秒数
long millisecond = localDateTime.toInstant(ZoneOffset.ofHours(8)).toEpochMilli();
System.out.println(millisecond);

1615803881877
2021-03-15T18:24:41.877
2021-03-15 18:24:41.877
2021-03-15T18:24:41.877
1615803881877

附录

en	🔉	cn
zone	zoʊn	n. 地带；vi. 分成区；vt. 使分成地带
timezone	ˈtaɪmzoʊn	时区；
milli	ˈmɪli	毫，千分之一
millisecond	ˈmɪlisekənd	毫秒