Spring Boot Controller Locale Not Changing with Parameter - spring

Question

I'm having some trouble with using Spring Boot with Kotlin to handle locale. I created these settings in my application.properties file:
spring.messages.basename=messages/messages
spring.messages.cache-seconds=-1
spring.messages.encoding=UTF-8
Then created an autowired instance of MessageSource in my controller:
#Autowired
lateinit var messageSource: MessageSource
When put a locale in the url as a parameter, the parameter doesn't seem to get picked up when I call LocaleContextHolder.getLocale(), so it is always en_US. Though, I can manually pick it up using #RequestParam(value="locale") locale: Locale as a parameter to my controller function and use it from there in the controller function, but not in other functions. I thought that spring boot LocaleContextHolder was supposed to hold the current locale based on the request URL automatically for the whole session.
I read an older article that mentioned using a LocaleChangeInterceptor bean as well as beans for MessageSource and LocaleResolver in your main class, but another article said Spring Boot doesn't require that. I tried it anyway with no difference. These are the functions I used:
#Bean
open fun localeResolver(): LocaleResolver {
val slr = SessionLocaleResolver()
slr.setDefaultLocale(Locale.US)
return slr
}
#Bean
open fun localeChangeInterceptor(): LocaleChangeInterceptor {
val localeChangeInterceptor = LocaleChangeInterceptor()
localeChangeInterceptor.paramName = "locale"
return localeChangeInterceptor
}
#Bean
open fun messageSource(): ResourceBundleMessageSource {
val source = ResourceBundleMessageSource()
source.setBasenames("messages/messages")
source.setDefaultEncoding("UTF-8")
return source
}
Any suggestions on what to try next other than capturing the locale manually and making it a parameter in every function that gets called by the controller? Thanks!

Answer 1

OK, looks like the missing piece was implementing a WebMvcConfigurerAdapter, setting up a SessionLocaleResolver bean, and overriding the addInterceptors function to manually add my LocaleChangeInterceptor. I used a separate Configuration class to do this.
#Configuration
open class CustomWebMvcConfigurerAdapter : WebMvcConfigurerAdapter() {
//internationalization beans
#Bean
open fun localeResolver(): LocaleResolver {
val slr = SessionLocaleResolver()
slr.setDefaultLocale(Locale.US)
return slr
}
#Bean
open fun localeChangeInterceptor(): LocaleChangeInterceptor {
val localeChangeInterceptor = LocaleChangeInterceptor()
localeChangeInterceptor.paramName = "locale"
return localeChangeInterceptor
}
override fun addInterceptors(registry: InterceptorRegistry?) {
registry?.addInterceptor(localeChangeInterceptor())
super.addInterceptors(registry)
}
}
I guess I misunderstood, thinking that Spring Boot handled the LocaleChangeInterceptor on it's own if you created the proper bean, but I guess you have to still override a WebMvcConfigurerAdapter and force the interceptor in there. If I've missed something and someone has a cleaner solution, I'd be happy to give you the accepted answer since what I'm doing here just feels like a messy workaround.