LocalContextHandler usage - spring

Question

I am very new to LocalContexHandler. I have read about it. From what I understood it is used to retrieve locale information in a java application.
I am passing the locale from the url as follows:
url?lang = fr
When I am trying to retrieve the locale in java application as follows:
Locale locale = LocaleContextHolder.getLocale();
It is giving null value. Can someone help me understand it's usage or is there any other alternative for the same?

Answer 1

If you want to pass locale in URL you must register LocaleChangeInterceptor interceptor and create LocaleResolver bean. For example SessionLocaleResolver stores chosen locale in session. Then LocaleContextHolder#getLocale will return not-null value. Take a look in Spring documentation to section Using locales. Below you can see basic Java configuration for you example.
If you want just use LocaleContextHolder you have to call LocaleContextHolder#setLocale from your code before calling LocaleContextHolder#getLocale. It's just simple holder class that stores LocaleContext in ThreadLocal variable.
#Configuration
#EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
// Rest of Web MVC configuration omitted
#Override
public void addInterceptors(InterceptorRegistry registry) {
super.addInterceptors(registry);
registry.addInterceptor(localeChangeInterceptor());
}
#Bean
public LocaleResolver localeResolver() {
SessionLocaleResolver sessionLocaleResolver = new SessionLocaleResolver();
sessionLocaleResolver.setDefaultLocale("fr");
return sessionLocaleResolver;
}
#Bean
public LocaleChangeInterceptor localeChangeInterceptor() {
LocaleChangeInterceptor interceptor = new LocaleChangeInterceptor();
interceptor.setParamName("lang");
return interceptor;
}
}