Get number format from OS

Question

This question seems insanely simple, yet I'm embarrased to say I haven't been able to figure out how it works.

I want my Java SE application to get its number format from whatever is configured in the OS. Just like any other application on that OS.

My target is primarily Windows. Consider this example in Windows:

I use this little example to check the result:

public class MyMain {
    public static void main(String[] args) {
        DecimalFormat decFormat = new DecimalFormat();
        DecimalFormatSymbols decSymbols = decFormat.getDecimalFormatSymbols();           
        System.out.println("Decimal separator is : " + decSymbols.getDecimalSeparator());
        System.out.println("Thousands separator is : " + decSymbols.getGroupingSeparator());
    }
}

With the screenshot example above my little Java example prints:

Decimal separator is : ,
Thousands separator is : .

I would have expected it to say that the decimal separator is a dot and the thousands separator is a comma - because that's what I've told Windows and that's what all other Windows applications pick up.

I'm under the impression that in Windows these settings take effect for new processes. I've tried restarting my IDE. Didn't help.

What am I doing wrong?

Answer 1

I've found the answer myself.

Starting from JDK8 you can ask Java to have the host's settings as your number one priority when resolving locale related stuff.

I've extended my example slightly:

public class MyMain {
    public static void main(String[] args) {
        DecimalFormat decFormat = new DecimalFormat();
        DecimalFormatSymbols decSymbols = decFormat.getDecimalFormatSymbols();
        String localeProvidersList = System.getProperty("java.locale.providers", "JRE,SPI");
        System.out.println("Decimal separator is : " + decSymbols.getDecimalSeparator());
        System.out.println("Thousands separator is : " + decSymbols.getGroupingSeparator());
        System.out.println("Locale providers list : " + localeProvidersList);
    }
}

Running my example above with -Djava.locale.providers=HOST,JRE,SPI gives:

Decimal separator is : .
Thousands separator is : ,
Locale providers list : HOST,JRE,SPI

Running without java.locale.providers defined gives:

Decimal separator is : ,
Thousands separator is : .
Locale providers list : JRE,SPI

Personally I would always run my Java applications with -Djava.locale.providers=HOST,.... because that will make my Java applications behave like native application do on that same host.

I found the answer deep inside the JDK8 javadocs. There's also a few notes about it in the Java 8 Enhancements docs.

Answer 2

You need to see: how to detect operating system language (locale) from java code. It seems like the bug was introduced in early Java 7 releases, and is somewhat fixed in later Java 7.

To test, I set my Window 7 Region to "French France". (Same as you show in your screen shot.)

Running this code:

System.out.println("default locale=" + Locale.getDefault());
System.out.println("user.language=" + System.getProperty("user.language"));
DecimalFormat decFormat = new DecimalFormat();
DecimalFormatSymbols decSymbols = decFormat.getDecimalFormatSymbols();
System.out.println("Decimal separator is : " + decSymbols.getDecimalSeparator());

with Java 6 (jdk1.6.0_45) output:

default locale=fr_FR

user.language=fr

Decimal separator is : ,

with Java 7 (jdk1.7.0_40) output:

default locale=en_US

user.language=en

Decimal separator is : ,

So only the decimal separator is correct with Java 7. One possible difference - is that I didn't change my "System Locale" from English (US) to French (France), because it required a restart. So perhaps that may affect what Java 7 is displaying for the Locale and user.language values.