@Nonnull
    @Override
    protected Object getCacheKey(
        @Nonnull
        final String viewName, @Nonnull
        final Locale locale) {
        return String.format("%s#%s", theme, super.getCacheKey(viewName, locale));
    }
{@link ThemeViewResolver} is a theme resolver that checks for a UI view in the specific theme before utilizing the
base UI view.

@author Daniel Frett
@since 5.2.0
support/cas-server-support-thymeleaf-core/src/main/java/org/apereo/cas/services/web/ThemeViewResolver.java