Happy New Year to everybody!!.

With Tapestry one of the advantages is that you can override almost everything but then there are always some parts which are less overridable. One such place is setting locale based on some custom criteria. The locale logic is embedded a bit deeper than you expect into the request processing cycle and that might give you an impression that you won’t be able to override it.

Of course I did find the solution (otherwise I would be writing to the very helpful mailing list Tapestry has) and it was so easy that you just got to admire Tapestry. All you have to do is decorate the ComponentEventLinkEncoder in the Application Module

public class AppModule {
    @Match("ComponentEventLinkEncoder")
    public ComponentEventLinkEncoder decorateComponentEventLinkEncoder(Logger logger,
        ComponentEventLinkEncoder delegate, DomainService domainService, ThreadLocale threadLocale) {
        return new DomainLinkTransformerInterceptor(logger, domainService, delegate, threadLocale);
    }
}

In our interceptor we intercept the calls to url decoding and set the locale there.

public class DomainLinkTransformerInterceptor implements ComponentEventLinkEncoder {

    private final Logger logger;

    private final DomainService domainService;

    private final ComponentEventLinkEncoder delegate;

    private ThreadLocale threadLocale;

    public DomainLinkTransformerInterceptor(Logger logger, DomainService domainService,
        ComponentEventLinkEncoder delegate, ThreadLocale threadLocale) {
        this.logger = logger;
        this.domainService = domainService;
        this.delegate = delegate;
        this.threadLocale = threadLocale;
    }

    @Override
    public Link createPageRenderLink(PageRenderRequestParameters parameters) {
        return delegate.createPageRenderLink(parameters);
    }

    @Override
    public Link createComponentEventLink(ComponentEventRequestParameters parameters, boolean forForm) {
        return delegate.createComponentEventLink(parameters, forForm);
    }

    @Override
    public ComponentEventRequestParameters decodeComponentEventRequest(Request request) {
        ComponentEventRequestParameters parameters = delegate.decodeComponentEventRequest(request);
        threadLocale.setLocale(domainService.getCurrentDomain().getLanguage().getLocale());
        logger.debug("For Domain {} setting locale to {}", domainService.getCurrentDomain(),
            threadLocale.getLocale());
        return parameters;
    }

    @Override
    public PageRenderRequestParameters decodePageRenderRequest(Request request) {
        PageRenderRequestParameters parameters = delegate.decodePageRenderRequest(request);
        threadLocale.setLocale(domainService.getCurrentDomain().getLanguage().getLocale());
        logger.debug("For Domain {} setting locale to {}", domainService.getCurrentDomain(),
            threadLocale.getLocale());
        return parameters;
    }

}

and you are done!.