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
符号 含义 展现形式 示例 ------ ------- ------------ ------- G era(时代) 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;
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 ！