Configure static field on boot with dependency injection Spring

Question

I need to configure a static field of a class when my application is booted, using objects obtained using dependency injection.
In particular, I have a class that manages notification channels, and that class should have some "default channels" to use, like the following:

public class CustomerNotificationPreference {
    static List<NotificationChannel> defaults = List.of();
    Long id;
    List<NotificationChannel> channels;
}

Everything works fine for non-static field, but I can't find a way to configure that defaults using dependency injection.

What I've tried so far is the following:

@SpringBootApplication(scanBasePackages = {"com..."})
@EnableJpaRepositories("com...")
public class MyApp {

    @Bean
    void configureDefaultChannel(
        TelegramBot telegramBot,
        JavaMailSender javaMailSender,
        @Value("${telegram-bot.default-chat}") String chatId,
        @Value("${mail.default-receiver}") String to
    ){
        CustomerNotificationPreference.setDefaults(List.of(
            new TelegramNotificationChannel(telegramBot, chatId),
            new MailNotificationChannel(javaMailSender, to)
        ));
    }

}

But obviously Spring doesn't allow this since a Bean must not be void (Invalid factory method 'configureDefaultChannel': needs to have a non-void return type!)... are there ways to do this kind of things?

Answer 1

You can't autowire static field directly, but you can set static field after application is initialized using @PostConstruct or catching ApplicationReadyEvent

public class MyApp {

    @Autowired
    TelegramBot telegramBot;

    @Autowired
    JavaMailSender javaMailSender

    @Value("${telegram-bot.default-chat}")
    String chatId;

    @Value("${mail.default-receiver}") 
    String to;

    @PostConstruct
    void setDefaults() {
        CustomerNotificationPreference.setDefaults(List.of(
            new TelegramNotificationChannel(telegramBot, chatId),
            new MailNotificationChannel(javaMailSender, to)
        ));
    }

    // OR

    @EventListener(ApplicationReadyEvent::class)
    void setDefaults() { 
        // same code as above
    }
    
}