Java时间系列(JDK8)--DateTimeFormatter的使用

梦里梦外; 2023-10-02 13:05 11阅读 0赞

原文网址：[Java时间系列(JDK8)--DateTimeFormatter的使用\_IT利刃出鞘的博客-CSDN博客][Java_JDK8_--DateTimeFormatter_IT_-CSDN]

## 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**

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 ###

<table> 
 <tbody> 
 <tr> 
 <td> 常量 </td> 
 <td> 示例 </td> 
 </tr> 
 <tr> 
 <td> BASIC_ISO_DATE </td> 
 <td> '20111203' </td> 
 </tr> 
 <tr> 
 <td> ISO_LOCAL_DATE </td> 
 <td> '2011-12-03' </td> 
 </tr> 
 <tr> 
 <td> ISO_OFFSET_DATE </td> 
 <td> '2011-12-03+01:00' </td> 
 </tr> 
 <tr> 
 <td> ISO_DATE </td> 
 <td> '2011-12-03' '2011-12-03+01:00' </td> 
 </tr> 
 <tr> 
 <td> ISO_LOCAL_TIME </td> 
 <td> '10:15' '10:15:30' </td> 
 </tr> 
 <tr> 
 <td> ISO_OFFSET_TIME </td> 
 <td> '10:15+01:00'&nbsp; '10:15:30+01:00' </td> 
 </tr> 
 <tr> 
 <td> ISO_TIME </td> 
 <td> '10:15' '10:15:30' '10:15:30+01:00' </td> 
 </tr> 
 <tr> 
 <td> ISO_LOCAL_DATE_TIME </td> 
 <td> '2011-12-03T10:15' '2011-12-03T10:15:30' </td> 
 </tr> 
 <tr> 
 <td> ISO_OFFSET_DATE_TIME </td> 
 <td> '2011-12-03T10:15:30.016+01:00' </td> 
 </tr> 
 <tr> 
 <td> ISO_ZONED_DATE_TIME </td> 
 <td> '2011-12-03T10:15:30.+01:00[Europe/Paris]' </td> 
 </tr> 
 <tr> 
 <td> ISO_DATE_TIME </td> 
 <td> '2011-12-03T10:15:30', '2011-12-03T10:15:30+01:00' '2011-12-03T10:15:30+01:00[Europe/Paris]' </td> 
 </tr> 
 <tr> 
 <td> ISO_ORDINAL_DATE </td> 
 <td> '2012-337' </td> 
 </tr> 
 <tr> 
 <td> ISO_WEEK_DATE </td> 
 <td> '2012-W48-6' </td> 
 </tr> 
 <tr> 
 <td> ISO_INSTANT </td> 
 <td> '2011-12-03T10:15:30Z' </td> 
 </tr> 
 </tbody> 
</table>

### 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

[Java_JDK8_--DateTimeFormatter_IT_-CSDN]: https://knife.blog.csdn.net/article/details/121004935