简介
说明
本文用示例介绍Java中的DateTimeFormatter的用法。
Java中的DateTimeFormatter是用来格式化JDK8的新的日期类的，比如：LocalDateTime、LocalDate、LocalTime。
线程安全
DateTimeFormatter是线程安全的。Date的格式化工具SimpleDateFormat不是线程安全的。
简单示例
package org.example.a;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class Demo{
public static void main(String[] args) {
LocalDateTime now = LocalDateTime.now();
//预定义的格式进行格式化
String date = DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(now);
System.out.println(date);
//自定义格式进行格式化
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
System.out.println(formatter.format(now));
// 或者这样写:
// System.out.println(now.format(formatter));
//自定义格式进行格式化（带毫秒）
DateTimeFormatter formatter1 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS");
System.out.println(formatter1.format(now));
}
}
执行结果
2020-07-29T23:03:03.014 2020-07-29 23:03:03 2020-07-29T23:03:03.014
示例大全
1.中文的月份
package com.example.a;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Locale;
public class Demo {
public static void main(String[] args) {
LocalDate now = LocalDate.now();
DateTimeFormatter formatter = null;
formatter = DateTimeFormatter.ofPattern("dd MM yyyy");
System.out.println(formatter.format(now));
formatter = DateTimeFormatter.ofPattern("dd MMM yyyy");
System.out.println(formatter.format(now));
formatter = DateTimeFormatter.ofPattern("dd MMMM yyyy");
System.out.println(formatter.format(now));
}
}
结果
19 04 2023 19 四月 2023 19 四月 2023
可以发现，大于等于三个MMM时，就能输出本地语言对应的月份。
2.英文的月份
要输出英文时，要指定语言。
package com.example.a;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Locale;
public class Demo {
public static void main(String[] args) {
LocalDate now = LocalDate.now();
DateTimeFormatter formatter = null;
formatter = DateTimeFormatter.ofPattern("dd M yyyy", Locale.ENGLISH);
System.out.println(formatter.format(now));
formatter = DateTimeFormatter.ofPattern("dd MM yyyy", Locale.ENGLISH);
System.out.println(formatter.format(now));
formatter = DateTimeFormatter.ofPattern("dd MMM yyyy", Locale.ENGLISH);
System.out.println(formatter.format(now));
formatter = DateTimeFormatter.ofPattern("dd MMMM yyyy", Locale.ENGLISH);
System.out.println(formatter.format(now));
formatter = DateTimeFormatter.ofPattern("dd MMMMM yyyy", Locale.ENGLISH);
System.out.println(formatter.format(now));
}
}
结果
19 4 2023 19 04 2023 19 Apr 2023 19 April 2023 19 A 2023
可以发现，M的个数可以是从1到5。
MMM：可以输出三位的月份。
MMMM： 可以输出整个月份单词。
格式参数
DateTimeFomatter类的一段注释。
| Symbol | Meaning | Presentation | Examples |
| G | era | text | AD; Anno Domini; A |
| u | year | year | 2004; 04 |
| y | year-of-era | year | 2004; 04 |
| D | day-of-year | number | 189 |
| M/L | month-of-year | number/text | 7; 07; Jul; July; J |
| d | day-of-month | number | 10 |
| Q/q | quarter-of-year | number/text | 3; 03; Q3; 3rd quarter |
| Y | week-based-year | year | 1996; 96 |
| w | week-of-week-based-year | number | 27 |
| W | week-of-month | number | 4 |
| E | day-of-week | text | Tue; Tuesday; T |
| e/c | localized day-of-week | number/text | 2; 02; Tue; Tuesday; T |
| F | week-of-month | number | 3 |
| a | am-pm-of-day | text | PM |
| h | clock-hour-of-am-pm (1-12) | number | 12 |
| K | hour-of-am-pm (0-11) | number | 0 |
| k | clock-hour-of-am-pm (1-24) | number | 0 |
| H | hour-of-day (0-23) | number | 0 |
| m | minute-of-hour | number | 30 |
| s | second-of-minute | number | 55 |
| S | fraction-of-second | fraction | 978 |
| A | milli-of-day | number | 1234 |
| n | nano-of-second | number | 987654321 |
| N | nano-of-day | number | 1234000000 |
| V | time-zone ID | zone-id | America/Los_Angeles; Z; -08:30 |
| z | time-zone name | zone-name | Pacific Standard Time; PST |
| O | localized zone-offset | offset-O | GMT+8; GMT+08:00; UTC-08:00; |
| X | zone-offset ‘Z’ for zero | offset-X | Z; -08; -0830; -08:30; -083015; -08:30:15; |
| x | zone-offset | offset-x | +0000; -08; -0830; -08:30; -083015; -08:30:15; |
| Z | zone-offset | offset-Z | +0000; -0800; -08:00; |
| p | pad next | pad modifier | 1 |
| ‘ | escape for text | delimiter | |
| ” | single quote | literal ‘ | |
| [ | optional section start | ||
| ] | optional section end | ||
| # | reserved for future use | ||
| { | reserved for future use | ||
| } | reserved for future use |
预定义格式
预定义格式化程序在DateTimeFormatter类中定义为常量。
大全
| 常量 | 示例 |
| BASIC_ISO_DATE | ‘20111203’ |
| ISO_LOCAL_DATE | ‘2011-12-03’ |
| ISO_OFFSET_DATE | ‘2011-12-03+01:00’ |
| ISO_DATE | ‘2011-12-03’ ‘2011-12-03+01:00’ |
| ISO_LOCAL_TIME | ’10:15′ ’10:15:30′ |
| ISO_OFFSET_TIME | ’10:15+01:00′ ’10:15:30+01:00′ |
| ISO_TIME | ’10:15′ ’10:15:30′ ’10:15:30+01:00′ |
| ISO_LOCAL_DATE_TIME | ‘2011-12-03T10:15’ ‘2011-12-03T10:15:30’ |
| ISO_OFFSET_DATE_TIME | ‘2011-12-03T10:15:30.016+01:00’ |
| ISO_ZONED_DATE_TIME | ‘2011-12-03T10:15:30.+01:00[Europe/Paris]’ |
| ISO_DATE_TIME | ‘2011-12-03T10:15:30’, ‘2011-12-03T10:15:30+01:00’ ‘2011-12-03T10:15:30+01:00[Europe/Paris]’ |
| ISO_ORDINAL_DATE | ‘2012-337’ |
| ISO_WEEK_DATE | ‘2012-W48-6’ |
| ISO_INSTANT | ‘2011-12-03T10:15:30Z’ |
注意事项
上边ISO之后都是对应的类名，比如：ISO_OFFSET_DATE_TIME是对应的OffsetDateTime类。OffsetDateTime是Java 8 中一个新的日期时间API，它表示一个日期-时间，包含时区偏移量。它比LocalDateTime就多了一个时区，其他用法都一样。
package com.example.a;
import java.time.OffsetDateTime;
import java.time.format.DateTimeFormatter;
public class Demo {
public static void main(String[] args) {
OffsetDateTime now = OffsetDateTime.now();
// 使用自带的格式
System.out.println(DateTimeFormatter.ISO_ZONED_DATE_TIME.format(now));
//或者：
System.out.println(now.format(DateTimeFormatter.ISO_OFFSET_DATE_TIME));
// 自定义格式
System.out.println(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ssXXX").format(now));
}
}
结果
2023-09-06T14:08:23.034+08:00 2023-09-06T14:08:23.034+08:00 2023-09-06T14:08:23+08:00
请先 ！