Micronaut i18n using MessageSource

To implement i18n in micronaut you need to have a bean that is a subclass of ResourceBundleMessageSource. This can be done by using a factory to create the bean:

@Factory
class AppConfig {
    @Bean
    MessageSource messageSource() {
        new ResourceBundleMessageSource('com.example.Messages')
    }
}

Or just having a @Singleton annotated class

@Singleton
class AppBundle extends ResourceBundleMessageSource {
       AppBundle() {
           super('com.example.Messages')
       }
}

In both cases we pass the baseName of our bundle. After this you create your locale specific property files Messages.properties, Messages_fr.properties etc in the src/main/resource/com/example directory.

Message.properties

greeting=Hello {person.name}

Then you can inject the bean into your controller or service to use it.

@Controller("/hello")
class HelloController {

    private final MessageSource messageSource

    HelloController(MessageSource messageSource) {
        this.messageSource = messageSource
    }

    @Get("/{lang}/{name}")
    String greeting(String lang, String name) {
        MessageSource.MessageContext messageContext =
                MessageSource.MessageContext.of(new Locale(lang), Collections.singletonMap("person.name", name))
        String template = messageSource.getMessage("greeting", messageContext).get()
        return messageSource.interpolate(template, messageContext)
    }
}

You will notice that even though the MessageContext passed into getMessage already contains the variables to resolve the message parameters, you actually still need to call interpolate to resolve them. This was raised as an issue on github and will no longer be the case in Micronaut 2.0.0

You can find a working example using micronaut 1.3.4 on github.