How to use "Functional bean definition Kotlin DSL" with Spring Boot and Spring WebFlux?

Question

At https://github.com/spring-projects/spring-framework/blob/master/spring-context/src/main/kotlin/org/springframework/context/support/BeanDefinitionDsl.kt the comment shows how to define Spring Beans via the new "Functional bean definition Kotlin DSL". I also found https://github.com/sdeleuze/spring-kotlin-functional. However, this example uses just plain Spring and not Spring Boot. Any hint how to use the DSL together with Spring Boot is appreciated.

Answer 1

Spring Boot is based on Java Config, but should allow experimental support of user-defined functional bean declaration DSL via ApplicationContextInitializer support as described here.

In practice, you should be able to declare your beans for example in a Beans.kt file containing a beans() function.

fun beans() = beans {
    // Define your bean with Kotlin DSL here
}

Then in order to make it taken in account by Boot when running main() and tests, create an ApplicationContextInitializer class as following:

class BeansInitializer : ApplicationContextInitializer<GenericApplicationContext> {

    override fun initialize(context: GenericApplicationContext) =
        beans().initialize(context)

}

And ultimately, declare this initializer in your application.properties file:

context.initializer.classes=com.example.BeansInitializer  

You will find a full example here and can also follow this issue about dedicated Spring Boot support for functional bean registration.

Answer 2

You can define your beans in *Config.kt file and implement initalize method of ApplicationContextInitializer interface.

override fun initialize(applicationContext: GenericApplicationContext) {
    ....
}

Some bean definition here.

bean<XServiceImpl>("xService")

bean("beanName") {
        BeanConstructor(ref("refBeanName"))
}

Answer 3

Another way to do it in Spring Boot would be :

fun main(args: Array<String>) {
    runApplication<DemoApplication>(*args) {
        addInitializers(
                beans {
                    // Define your bean with Kotlin DSL here
                }
        )
    }
}

Answer 4

That same example project you mentioned has a boot git branch, with the BeanDefinitionDsl configuration for Spring Boot in a Beans.kt file. That is not how you should use git branches...