Spring 是否在 Kotlin object 中自动接线？

Question

In the Spring framework, by default, bean scope is Singleton. But with Kotlin, we can easily create a Singleton object. Just need to do

object SimpleService {
  fun businessFunction() = ...
}

If we try to use Spring to manage the scope of a Kotlin object , would it be some kind of redundancy? Because I should only need to do...

• Rather than create a class and have Spring manage objects, I just need to create a Kotlin object (singleton).

• If we don't want to violate the interface segregation principle , we will create an interface and a Service just needs to implement it. And only need to register to Spring something like: @Bean IMyService = SimpleSerice

The only one thing Spring can help us with Kotlin is Spring Data (Create Repository Interface without implementation). But I think we only need to integrate with some open source for it (or create new one)

I'm concerned that Spring might be totally redundant and heavy for Kotlin.

Answer 1

Spring Beans have a different purpose than Kotlin objects and are not comparable per se.

With Spring beans, you get (environment-specific) configuration, dependency injection, ... . You can actually create multiple beans of the same type with different values.

When it comes to testing, you can use slices or tailor tests yourself to only instantiate the beans you absolutely need for the test. Furthermore, you can mock them.

TBOMK, kotlin object expressions are initialized when the containing file is loaded - which might not be too transparent in larger projects. This has the side effect that you might not be able to control it in tests. Also, configuration and injections have to be achieved differently. Never tried mocking... .

I use Kotlin with Spring and have various Spring beans in action. I use companion objects and object expressions whenever I have a very static context with fast initialisation. So these objects serve more static concerns while spring beans serve dynamic ones.