Re: #544: Localization & BeanValidation


 

Hey Pavel,

The struggle here is with the SupportedLanguagesProvider - it feels like it should be used for something more than BV - I think it's fair to say that if localizaiton of BV error messages is the sole purpose of such provider, it shouldn't be introduced. And I can't think of any other sensible use right now.

I would like to take the opportunity to describe what MVC did to support internationalization which relates to the issue we are discussing here. As MVC builds on top of JAX-RS, this may (or may not) be interesting for you.

For MVC we identified a few locale-dependent aspects which we had to support:
  1. Data type conversion as part of the data binding mechanism needs to be locale aware. So something like @FormParam("price") BigDecimal price needs to be parsed according to the number formatting rules of the specific locale.
  2. Formatting data according to locale dependent rules when rending the view (date format / number format). This certainly isn't something relevant for JAX-RS.
  3. Generating binding and validation errors message in the specific language. This is basically what we are talking about here.
To support these scenarios we defined the term "request locale" as the locale which is used for any locale-dependent operation within the lifecycle of a request. The request locale is resolved for each request using the following SPI:

  public interface LocaleResolver {
    Locale resolveLocale(LocaleResolverContext context);
  }

The default implementation basically resolves the locale by parsing the Accept-Locale request header and resolving the locale with the highest priority. 

But developers can customize this by providing their own resolver. So if the developer wants to support only a specific subset of locales, he could simply create a custom resolver and match the supported locales against the Accept-Locale header as described in Pavel's previous mail.

You can see the full SPI here:


All the details are described in the MVC spec document (pages 37-38):


I'm not sure if anything described here could be useful for JAX-RS. Of cause we (the MVC EG) would be happy to see any of our APIs to be integrated into JAX-RS.

Christian


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