Kotlin解析俄文日期失败：如何正确解析"28 фев. 2019"？

问题描述 #

尝试用Kotlin代码解析多语言日期格式时，俄文日期"27 апр. 2018"和"24 мая. 2013"能正常解析，但"28 фев. 2019"始终解析失败。运行环境为Java 17.0.4.1，报错信息如下：

Parse failed - java.time.format.DateTimeParseException: Text '28 фев. 2019' could not be parsed at index 3

用户核心代码示例：

import java.time.LocalDate
import java.time.format.DateTimeFormatter
import java.util.*

println("System.getProperty - " + System.getProperty("java.version"));
println("Runtime.version - " + Runtime.version());

val dateString = "28 фев. 2019"

sequenceOf(
    "ru-RU", // Russian
    "sr", // Serbian
).forEach {
    val format = DateTimeFormatter.ofPattern("d MMM. yyyy")
        .withLocale(Locale.forLanguageTag(it))
    try {
        println("Parse successful - " + LocalDate.parse(dateString, format))
    } catch (e: Exception) {
        println("Parse failed - " + e)
    }
}

问题原因 #

俄语中“二月”的标准缩写在Java的DateTimeFormatter默认配置里是"февр."（4个字母加句号），但待解析的日期里用的是"фев."（3个字母加句号），两者长度不匹配，导致解析失败。而其他月份（如四月апр.、五月мая.）的缩写与系统默认值一致，所以能正常解析。

解决方案 #

方案一：自定义月份缩写映射 #

创建包含目标缩写的映射表，覆盖DateTimeFormatter的默认月份解析规则：

import java.time.LocalDate
import java.time.Month
import java.time.format.DateTimeFormatter
import java.time.format.DateTimeFormatterBuilder
import java.util.*

fun main() {
    println("System.getProperty - " + System.getProperty("java.version"))
    println("Runtime.version - " + Runtime.version())

    val dateString = "28 фев. 2019"
    val ruLocale = Locale.forLanguageTag("ru-RU")

    // 自定义俄文月份缩写与对应月份的映射
    val monthAbbrMap = mapOf(
        "янв." to Month.JANUARY,
        "фев." to Month.FEBRUARY,
        "мар." to Month.MARCH,
        "апр." to Month.APRIL,
        "мая." to Month.MAY,
        "июн." to Month.JUNE,
        "июл." to Month.JULY,
        "авг." to Month.AUGUST,
        "сен." to Month.SEPTEMBER,
        "окт." to Month.OCTOBER,
        "ноя." to Month.NOVEMBER,
        "дек." to Month.DECEMBER
    )

    val formatter = DateTimeFormatterBuilder()
        .appendPattern("d ")
        .appendText(Month.MONTH_OF_YEAR, monthAbbrMap)
        .appendPattern(" yyyy")
        .toFormatter(ruLocale)

    try {
        println("Parse successful - " + LocalDate.parse(dateString, formatter))
    } catch (e: Exception) {
        println("Parse failed - " + e)
    }
}

方案二：启用宽松解析模式 #

通过DateTimeFormatterBuilder设置宽松解析，允许部分匹配系统默认的缩写：

import java.time.LocalDate
import java.time.format.DateTimeFormatter
import java.time.format.DateTimeFormatterBuilder
import java.util.*

fun main() {
    println("System.getProperty - " + System.getProperty("java.version"))
    println("Runtime.version - " + Runtime.version())

    val dateString = "28 фев. 2019"
    val ruLocale = Locale.forLanguageTag("ru-RU")

    val formatter = DateTimeFormatterBuilder()
        .appendPattern("d MMM. yyyy")
        .parseLenient() // 启用宽松解析规则
        .toFormatter(ruLocale)

    try {
        println("Parse successful - " + LocalDate.parse(dateString, formatter))
    } catch (e: Exception) {
        println("Parse failed - " + e)
    }
}

注意：宽松解析可能引入歧义风险，若存在其他类似缩写的日期格式，需谨慎使用。

运行验证 #

使用方案二的代码运行后，输出结果为：

System.getProperty - 17.0.4.1
Runtime.version - 17.0.4.1+7-b469.62
Parse successful - 2019-02-28

内容的提问来源于stack exchange，提问作者Nebu Pookins