Spring's @Import annotation offers functions such as <import/> an element in Spring XML. By utilizing the @Import annotation, you can import at least one @Configuration class. It can also import classes that contain no less than one @Bean function.  

The content of Boo.kt is as follows:

class Foo{
    init {
        println("This is class Foo")
    }
}
class Boo{
    init {
        println("This is class Boo")
    }
}

The content of ConfigBoo.kt is as follows:

@Configuration
class ConfigFoo {
    @Bean
    fun foo(): Foo{
        return Foo()
    }
}

@Configuration
@Import(ConfigFoo::class)
class ConfigBoo {
    @Bean
    fun foo(): Boo {
        return Boo()
    }
}

You don't need to specify both ConfigFoo.class and ConfigBoo.class when instantiating the context, so the following code isn't required when you initialize AnnotationConfigApplicationContext:

val applicationContext = AnnotationConfigApplicationContext(ConfigBoo::class.java, ConfigFoo::class.java)

As bean definitions of ConfigFoo are already loaded by using the @Import annotation with the ConfigBoo bean, only ConfigBoo needs to be explicitly specified:

val applicationContext = AnnotationConfigApplicationContext(ConfigBoo::class.java)

Here's the modified complete code of the main function of  MainAppImport.kt:

fun main(args: Array<String>) {
    val applicationContext = AnnotationConfigApplicationContext(ConfigBoo::class.java)

    //both beans Boo and Foo will be available...
    val boo: Boo = applicationContext.getBean(Boo::class.java)
    val foo: Foo = applicationContext.getBean(Foo::class.java)
}

The result will be as follows:

This is class Boo
This is class Foo