C# 日期型 JSON 序列化后毫秒部分的 7 位数字是啥？

使用 Newtonsoft.Json 来序列化日期型字段时，其毫秒部分有 7 为小数。一直也没太在意，但昨天在 Java 中使用 SimpleDateFormat 反序列化时却发现没有对应的格式说明符。

Newtonsoft.Json 序列化时默认使用了 IsoDateTimeConverter，其序列化后结果为 2019-09-23T15:20:06.4086491+08:00。

而 Java 中 SimpleDateFormat 最接近的一种格式为 yyyy-MM-dd'T'HH:mm:ss.SSSXXX，其毫秒部分只有 3 位小数，反序列化上面的日期字符串会报错。

为啥会失败？首先要搞清楚这 7 位数字是啥。请参考 MSDN 的文档：

The "fffffff" custom format specifier
The "fffffff" custom format specifier represents the seven most significant digits of the seconds fraction; that is, it represents the ten millionths of a second in a date and time value.
Although it's possible to display the ten millionths of a second component of a time value, that value may not be meaningful. The precision of date and time values depends on the resolution of the system clock. On the Windows NT 3.5 (and later) and Windows Vista operating systems, the clock's resolution is approximately 10-15 milliseconds.

"fffffff" 表示千万分之一精度的秒，但是后面又说了，在 Windows 中其精度由系统时钟决定，大约在 10-15 毫秒。换句话说，在 Windows 中这个精度是几乎是没有意义的。（不知道在 Linux 中其精度是多少？）

C# 中自定义日期型的序列化方法

既然几乎没意义，那么就可以放心的删掉了。参考这篇博客，有两种方式可以修改日期型的序列化格式，具体使用哪种方式根据项目需要而定。

在序列化时通过传递一个 JsonSerializerSettings 来配置日期的序列化格式

csharp

JsonConvert.SerializeObject(obj, new JsonSerializerSettings()
{
    DateFormatString = "yyyy-MM-dd'T'HH:mm:ss.fffzzz",
});

在需要自定义格式的日期字段上添加 [JsonConverter(typeof(CustomDateTimeConverter))] 特性

csharp

public class CustomDateTimeConverter : IsoDateTimeConverter
{
    public CustomDateTimeConverter()
    {
        DateTimeFormat = "yyyy-MM-dd'T'HH:mm:ss.fffzzz";
    }
}

Scala 中的反序列化处理

在 Java 中使用 new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX") 的 parse 方法可以正确的转成 Date 型。

这里项目使用的 Genson 的 Scala 版的包。自定义 JSON 反序列化的方法如下：

定义 CustomGenson.scala 类：

scala

import java.text.SimpleDateFormat

import com.owlike.genson._

object CustomGenson {
val customGenson = new ScalaGenson(
    new GensonBuilder()
    .useDateFormat(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX"))
    .withBundle(ScalaBundle().useOnlyConstructorFields(false))
    .create()
)
}

引用上面自定义的包，反序列化的方法不变。
scala
```
import CustomGenson.customGenson._

fromJson[ModelName](strJson)
```
1
2
3

C# 中日期型格式化的格式说明符

摘自 MSDN

Format specifier	Description	Examples
`"d"`	The day of the month, from 1 through 31.	2009-06-01T13:45:30 -> 1 2009-06-15T13:45:30 -> 15
`"dd"`	The day of the month, from 01 through 31.	2009-06-01T13:45:30 -> 01 2009-06-15T13:45:30 -> 15
`"ddd"`	The abbreviated name of the day of the week.	2009-06-15T13:45:30 -> Mon (en-US) 2009-06-15T13:45:30 -> Пн (ru-RU) 2009-06-15T13:45:30 -> lun. (fr-FR)
`"dddd"`	The full name of the day of the week.	2009-06-15T13:45:30 -> Monday (en-US) 2009-06-15T13:45:30 -> понедельник (ru-RU) 2009-06-15T13:45:30 -> lundi (fr-FR)
`"f"`	The tenths of a second in a date and time value.	2009-06-15T13:45:30.6170000 -> 6 2009-06-15T13:45:30.05 -> 0
`"ff"`	The hundredths of a second in a date and time value.	2009-06-15T13:45:30.6170000 -> 61 2009-06-15T13:45:30.0050000 -> 00
`"fff"`	The milliseconds in a date and time value.	6/15/2009 13:45:30.617 -> 617 6/15/2009 13:45:30.0005 -> 000
`"ffff"`	The ten thousandths of a second in a date and time value.	2009-06-15T13:45:30.6175000 -> 6175 2009-06-15T13:45:30.0000500 -> 0000
`"fffff"`	The hundred thousandths of a second in a date and time value.	2009-06-15T13:45:30.6175400 -> 61754 6/15/2009 13:45:30.000005 -> 00000
`"ffffff"`	The millionths of a second in a date and time value.	2009-06-15T13:45:30.6175420 -> 617542 2009-06-15T13:45:30.0000005 -> 000000
`"fffffff"`	The ten millionths of a second in a date and time value.	2009-06-15T13:45:30.6175425 -> 6175425 2009-06-15T13:45:30.0001150 -> 0001150
`"F"`	If non-zero, the tenths of a second in a date and time value.	2009-06-15T13:45:30.6170000 -> 6 2009-06-15T13:45:30.0500000 -> (no output)
`"FF"`	If non-zero, the hundredths of a second in a date and time value.	2009-06-15T13:45:30.6170000 -> 61 2009-06-15T13:45:30.0050000 -> (no output)
`"FFF"`	If non-zero, the milliseconds in a date and time value.	2009-06-15T13:45:30.6170000 -> 617 2009-06-15T13:45:30.0005000 -> (no output)
`"FFFF"`	If non-zero, the ten thousandths of a second in a date and time value.	2009-06-15T13:45:30.5275000 -> 5275 2009-06-15T13:45:30.0000500 -> (no output)
`"FFFFF"`	If non-zero, the hundred thousandths of a second in a date and time value.	2009-06-15T13:45:30.6175400 -> 61754 2009-06-15T13:45:30.0000050 -> (no output)
`"FFFFFF"`	If non-zero, the millionths of a second in a date and time value.	2009-06-15T13:45:30.6175420 -> 617542 2009-06-15T13:45:30.0000005 -> (no output)
`"FFFFFFF"`	If non-zero, the ten millionths of a second in a date and time value.	2009-06-15T13:45:30.6175425 -> 6175425 2009-06-15T13:45:30.0001150 -> 000115
`"g", "gg"`	The period or era.	2009-06-15T13:45:30.6170000 -> A.D.
`"h"`	The hour, using a 12-hour clock from 1 to 12.	2009-06-15T01:45:30 -> 1 2009-06-15T13:45:30 -> 1
`"hh"`	The hour, using a 12-hour clock from 01 to 12.	2009-06-15T01:45:30 -> 01 2009-06-15T13:45:30 -> 01
`"H"`	The hour, using a 24-hour clock from 0 to 23.	2009-06-15T01:45:30 -> 1 2009-06-15T13:45:30 -> 13
`"HH"`	The hour, using a 24-hour clock from 00 to 23.	2009-06-15T01:45:30 -> 01 2009-06-15T13:45:30 -> 13
`"K"`	Time zone information.	2009-06-15T13:45:30, Kind Unspecified -> 2009-06-15T13:45:30, Kind Utc -> Z 2009-06-15T13:45:30, Kind Local -> -07:00 (depends on local computer settings) 2009-06-15T01:45:30-07:00 --> -07:00 2009-06-15T08:45:30+00:00 --> +00:00
`"m"`	The minute, from 0 through 59.	2009-06-15T01:09:30 -> 9 2009-06-15T13:29:30 -> 29
`"mm"`	The minute, from 00 through 59.	2009-06-15T01:09:30 -> 09 2009-06-15T01:45:30 -> 45
`"M"`	The month, from 1 through 12.	2009-06-15T13:45:30 -> 6
`"MM"`	The month, from 01 through 12.	2009-06-15T13:45:30 -> 06
`"MMM"`	The abbreviated name of the month.	2009-06-15T13:45:30 -> Jun (en-US) 2009-06-15T13:45:30 -> juin (fr-FR) 2009-06-15T13:45:30 -> Jun (zu-ZA)
`"MMMM"`	The full name of the month.	2009-06-15T13:45:30 -> June (en-US) 2009-06-15T13:45:30 -> juni (da-DK) 2009-06-15T13:45:30 -> uJuni (zu-ZA)
`"s"`	The second, from 0 through 59.	2009-06-15T13:45:09 -> 9
`"ss"`	The second, from 00 through 59.	2009-06-15T13:45:09 -> 09
`"t"`	The first character of the AM/PM designator.	2009-06-15T13:45:30 -> P (en-US) 2009-06-15T13:45:30 -> 午 (ja-JP) 2009-06-15T13:45:30 -> (fr-FR)
`"tt"`	The AM/PM designator.	2009-06-15T13:45:30 -> PM (en-US) 2009-06-15T13:45:30 -> 午後 (ja-JP) 2009-06-15T13:45:30 -> (fr-FR)
`"y"`	The year, from 0 to 99.	0001-01-01T00:00:00 -> 1 0900-01-01T00:00:00 -> 0 1900-01-01T00:00:00 -> 0 2009-06-15T13:45:30 -> 9 2019-06-15T13:45:30 -> 19
`"yy"`	The year, from 00 to 99.	0001-01-01T00:00:00 -> 01 0900-01-01T00:00:00 -> 00 1900-01-01T00:00:00 -> 00 2019-06-15T13:45:30 -> 19
`"yyy"`	The year, with a minimum of three digits.	0001-01-01T00:00:00 -> 001 0900-01-01T00:00:00 -> 900 1900-01-01T00:00:00 -> 1900 2009-06-15T13:45:30 -> 2009
`"yyyy"`	The year as a four-digit number.	0001-01-01T00:00:00 -> 0001 0900-01-01T00:00:00 -> 0900 1900-01-01T00:00:00 -> 1900 2009-06-15T13:45:30 -> 2009
`"yyyyy"`	The year as a five-digit number.	0001-01-01T00:00:00 -> 00001 2009-06-15T13:45:30 -> 02009
`"z"`	Hours offset from UTC, with no leading zeros.	2009-06-15T13:45:30-07:00 -> -7
`"zz"`	Hours offset from UTC, with a leading zero for a single-digit value.	2009-06-15T13:45:30-07:00 -> -07
`"zzz"`	Hours and minutes offset from UTC.	2009-06-15T13:45:30-07:00 -> -07:00
`":"`	The time separator.	2009-06-15T13:45:30 -> : (en-US) 2009-06-15T13:45:30 -> . (it-IT) 2009-06-15T13:45:30 -> : (ja-JP)
`"/"`	The date separator.	2009-06-15T13:45:30 -> / (en-US) 2009-06-15T13:45:30 -> - (ar-DZ) 2009-06-15T13:45:30 -> . (tr-TR)
`"string"`	Literal string delimiter.	2009-06-15T13:45:30 ("arr:" h:m t) -> arr: 1:45 P 2009-06-15T13:45:30 ('arr:' h:m t) -> arr: 1:45 P
`%`	Defines the following character as a custom format specifier.	2009-06-15T13:45:30 (%h) -> 1
`\`	The escape character.	2009-06-15T13:45:30 (h \h) -> 1 h
`Any other character`	The character is copied to the result string unchanged.	2009-06-15T01:45:30 (arr hh:mm t) -> arr 01:45 A

Java 中日期型格式化的格式说明符

摘自 SimpleDateFormat 的注释。

Letter	Date or Time Component	Presentation	Examples
`G`	Era designator	Text	AD
`y`	Year	Year	1996; 96
`Y`	Week year	Year	2009; 09
`M`	Month in year (context sensitive)	Month	July; Jul; 07
`L`	Month in year (standalone form)	Month	July; Jul; 07
`w`	Week in year	Number	27
`W`	Week in month	Number	2
`D`	Day in year	Number	189
`d`	Day in month	Number	10
`F`	Day of week in month	Number	2
`E`	Day name in week	Text	Tuesday; Tue
`u`	Day number of week (1 = Monday, ..., 7 = Sunday)	Number	1
`a`	Am/pm marker	Text	PM
`H`	Hour in day (0-23)	Number	0
`k`	Hour in day (1-24)	Number	24
`K`	Hour in am/pm (0-11)	Number	0
`h`	Hour in am/pm (1-12)	Number	12
`m`	Minute in hour	Number	30
`s`	Second in minute	Number	55
`S`	Millisecond	Number	978
`z`	Time zone	General time zone	Pacific Standard Time; PST; GMT-08:00
`Z`	Time zone	RFC 822 time zone	-0800
`X`	Time zone	ISO 8601 time zone	-08; -0800; -08:00

Examples

Date and Time Pattern	Result
`"yyyy.MM.dd G 'at' HH:mm:ss z"`	2001.07.04 AD at 12:08:56 PDT
`"EEE, MMM d, ''yy"`	Wed, Jul 4, '01
`"h:mm a"`	12:08 PM
`"hh 'o''clock' a, zzzz"`	12 o'clock PM, Pacific Daylight Time
`"K:mm a, z"`	0:08 PM, PDT
`"yyyyy.MMMMM.dd GGG hh:mm aaa"`	02001.July.04 AD 12:08 PM
`"EEE, d MMM yyyy HH:mm:ss Z"`	Wed, 4 Jul 2001 12:08:56 -0700
`"yyMMddHHmmssZ"`	010704120856-0700
`"yyyy-MM-dd'T'HH:mm:ss.SSSZ"`	2001-07-04T12:08:56.235-0700
`"yyyy-MM-dd'T'HH:mm:ss.SSSXXX"`	2001-07-04T12:08:56.235-07:00
`"YYYY-'W'ww-u"`	2001-W27-3

C# 日期型 JSON 序列化后毫秒部分的 7 位数字是啥？ ​

The "fffffff" custom format specifier ​

C# 中自定义日期型的序列化方法 ​

Scala 中的反序列化处理 ​

C# 中日期型格式化的格式说明符 ​

Java 中日期型格式化的格式说明符 ​

Examples ​