与 Bash 相比，Java 中的区域设置区分大小写不一致

Question

当我尝试用波兰语格式化日期时，我得到了一致的格式：

new SimpleDateFormat("EEEE", Locale.forLanguageTag("pl-PL")).format(new Date())

结果

wtorek

在bash中的相同结果：

LC_ALL=pl_PL
$ date +"%A %b %d"
wtorek maj 22

注意 wtorek.

中的两个小写 w

当我对捷克语执行此操作时，结果不一致：

new SimpleDateFormat("EEEE", Locale.forLanguageTag("cs-CZ").format(new Date())

结果

Pondělí

当运行在 bash:

$ LC_ALL=cs_CZ 
$ date +"%A %b %d"
pondělí kvě 21

注意 Java 结果中的大写字母 P。这是怎么发生的？这是否意味着 SimpleDateFormat 不使用系统上安装的标准语言环境？

Answer 1

Does it mean SimpleDateFormat doesn't use standard Locales installed on the system

是的，不使用系统语言环境，可用的语言环境取决于 JVM/JRE 供应商。例如检查 JRE 目录中的 lib\ext\localedata.jar。解压后可以找到文件：sun\text\resources\cs\FormatData_cs_CZ.class 反编译为：

public class FormatData_cs extends ParallelListResourceBundle
{
    @Override
    protected final Object[][] getContents() {
        return new Object[][] { { "MonthNames", 
        { "ledna", "\u00fanora", "b\u0159ezna", "dubna", "kv\u011btna", "\u010dervna", "\u010dervence", "srpna", "z\u00e1\u0159\u00ed", "\u0159\u00edjna", "listopadu", "prosince", "" } }, 
        { "standalone.MonthNames", { "leden", "\u00fanor", "b\u0159ezen", "duben", "kv\u011bten", "\u010derven", "\u010dervenec", "srpen", "z\u00e1\u0159\u00ed", "\u0159\u00edjen", "listopad", "prosinec", "" } }, 
        { "MonthAbbreviations", { "Led", "\u00dano", "B\u0159e", "Dub", "Kv\u011b", "\u010cer", "\u010cvc", "Srp", "Z\u00e1\u0159", "\u0158\u00edj", "Lis", "Pro", "" } }, 
        { "standalone.MonthAbbreviations", { "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX", "X", "XI", "XII", "" } }, 
        { "MonthNarrows", { "l", "\u00fa", "b", "d", "k", "\u010d", "\u010d", "s", "z", "\u0159", "l", "p", "" } },
        { "standalone.MonthNarrows", { "l", "\u00fa", "b", "d", "k", "\u010d", "\u010d", "s", "z", "\u0159", "l", "p", "" } }, 
        { "DayNames", { "Ned\u011ble", "Pond\u011bl\u00ed", "\u00dater\u00fd", "St\u0159eda", "\u010ctvrtek", "P\u00e1tek", "Sobota" } }, 
        { "standalone.DayNames", { "ned\u011ble", "pond\u011bl\u00ed", "\u00fater\u00fd", "st\u0159eda", "\u010dtvrtek", "p\u00e1tek", "sobota" } }, 
        { "DayAbbreviations", { "Ne", "Po", "\u00dat", "St", "\u010ct", "P\u00e1", "So" } }, 
        { "standalone.DayAbbreviations", { "ne", "po", "\u00fat", "st", "\u010dt", "p\u00e1", "so" } }, 
        { "DayNarrows", { "N", "P", "\u00da", "S", "\u010c", "P", "S" } }, 
        { "standalone.DayNarrows", { "N", "P", "\u00da", "S", "\u010c", "P", "S" } },
        { "AmPmMarkers", { "dop.", "odp." } }, 
        { "Eras", { "p\u0159.Kr.", "po Kr." } }, 
        { "short.Eras", { "p\u0159. n. l.", "n. l." } }, 
        { "narrow.Eras", { "p\u0159.n.l.", "n. l." } }, 
        { "NumberElements", { ",", " ", ";", "%", "0", "#", "-", "E", "\u2030", "\u221e", "\ufffd" } }, 
        { "TimePatterns", { "H:mm:ss z", "H:mm:ss z", "H:mm:ss", "H:mm" } }, 
        { "DatePatterns", { "EEEE, d. MMMM yyyy", "d. MMMM yyyy", "d.M.yyyy", "d.M.yy" } }, 
        { "DateTimePatterns", { "{1} {0}" } }, 
        { "DateTimePatternChars", "GuMtkHmsSEDFwWahKzZ" } };
    }
}

并在 "DayNames" 中包含 "Pond\u011bl\u00ed"。

Answer 2

Java 从最多四个来源获取其语言环境数据（包括不同语言环境中星期几的名称）。是的，主机操作系统是其中之一，但不是默认的。引用 the LocaleServiceProvider documentation:

Java Runtime Environment provides the following four locale providers:

"CLDR": A provider based on Unicode Consortium's CLDR Project.

"COMPAT": represents the locale sensitive services that is compatible with the prior JDK releases up to JDK8 (same as JDK8's "JRE").

"SPI": represents the locale sensitive services implementing the subclasses of this LocaleServiceProvider class.

"HOST": A provider that reflects the user's custom settings in the underlying operating system. This provider may not be available, depending on the Java Runtime Environment implementation.

"JRE": represents a synonym to "COMPAT". This name is deprecated and will be removed in the future release of JDK.

最多 Java 8 JRE 是默认设置。我正在使用 java.time 因为没有人应该为过时的 SimpleDateFormat:

而烦恼

    DateTimeFormatter dayOfWeekFormatter 
            = DateTimeFormatter.ofPattern("EEEE", Locale.forLanguageTag("cs-CZ"));
    LocalDate date = LocalDate.now(ZoneId.of("Europe/Prague"));
    System.out.println(date.format(dayOfWeekFormatter));

我的 Oracle jdk1.8.0_131 上的输出运行ning 与您的结果一致（大写 S）：

Středa

我们可以控制通过系统使用的语言环境数据属性。例如，要更喜欢 CLDR，可以运行带有 VM 命令行选项 -Djava.locale.providers=CLDR,COMPAT 的程序，或者在程序开头插入以下行：

    System.setProperty("java.locale.providers", "CLDR,COMPAT");

středa

现在我们得到小写 s。

我在 mac 上的 shellOS Sierra 10.12.6 只提供 Wednesday，所以显然我的 OS 没有捷克语言环境数据（这听起来很奇怪；可能问题出在其他地方），因此对我来说不是一个选择。您可以尝试将 HOST 放在上述语言环境提供程序字符串的前面，看看您得到的内容是否与您的 bash.

一致

在 Java 9 和更高版本中，CLDR 是默认值。所以运行在 jdk9.0.4 上使用相同的代码片段而不设置任何系统属性也给出了小写的星期几：

středa

与 Bash 相比，Java 中的区域设置区分大小写不一致

Inconsistent locale case sensitivity in Java compared to Bash

java

bash

locale

date

simpledateformat