重新加载java类中的静态字段

Question

I have a class in java which has a number of static final strings and one static Locale variable.

These Strings are basically keys to a messagebundle which return the translated Strings using the locale.

ie,

public static Locale locale = Locale.getDefault();
public static String MSG1 = Translator.get(locale, "MSG1");
//Similar Strings.

This locale variable is set at runtime based on the browser locale. But since these are static variables, they are already initialized with the default locale and changes to the locale variable does not have any effect.

Is there a way to "reload" these strings everytime the locale variable is changed?

I don't want to make the obvious change(making all the strings non static and initializing locale in constructor/method) because this class has a lot of messages(250+) and is used in too many places.

Answer 1

Yes. While you can't get Java to run the assignments again, you can move the assignments into a method instead:

public static String MSG1;

public static void setLocale(Locale locale) {
   MSG1 = Translator.get(locale, "MSG1");
}

static {
    setLocale( Locale.getDefault() );
}

After that, you can use the method setLocale() to switch the locale. When the class is loaded for the first time, the locale is set using the static initializer block at the end.

[EDIT] This of course doesn't work in a multi-threaded environment: Static variables are global (= shared between all threads). What's worse: Due to Java's memory model, a change of the variable in thread 1 might not be visible at any specific point in time to any other threads.

If you need this in a web server, then you can't use static variables anymore. I suggest to create an instance of the class and convert all the static fields into methods. Then you can create this instance in a Filter and put it in the request and configure it correctly.

public class I18nHelper {
    public static I18nHelper get( HttpServletRequest request ) {
        return (HttpServletRequest) request.getAttribute( "I18nHelper" );
    }

    private Locale locale;

    public I18nHelper(Locale locale) {
        this.locale = locale;
    }

    public String msg1() {
        return Translator.get(locale, "MSG1");
    }
}

This approach has another huge advantage: You can pass type-safe arguments!

    public String fileNotFoundMsg( File file ) {
        ... format message with parameter "file" and return it...
    }

Answer 2

Instead of creating a local reference in every place that uses this variable, just use the static method itself.

Meaning, if you have a method:

public void doSomething() {
   if(locale.isSomeLocale()) { // Do something }
}

Just do:

public void doSomething() {
   if(Locale.getDefault().isSomeLocale()) { // Do something }
}

I think that's the cleanest option you can have. If you try to update 200+ local variables, every time the static variable changes, you'll have a terrible mess. This way, every point in your code is aligned with the locale you use.

Answer 3

But since these are static variables, they are already initialized with the default locale and changes to the locale variable does not have any effect.

You can reassign a static variable, unless, it's final.