Kotlin & Spring Boot @ConfigurationProperties

Update: As of Spring Boot 2.2.0, you can use data classes as follows:

@ConstructorBinding
@ConfigurationProperties("example.kotlin")
data class KotlinExampleProperties(
        val name: String,
        val description: String,
        val myService: MyService) {

    data class MyService(
            val apiToken: String,
            val uri: URI
    )
}

For further reference, see the official documentation.

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Obsolete as of Spring Boot 2.2.0, Issue closed

As stated in the docs: A "Java Bean“ has to be provided in order to use ConfigurationProperties. This means your properties need to have getters and setters, thus val is not possible at the moment.

Getters and setters are usually mandatory, since binding is via standard Java Beans property descriptors, just like in Spring MVC. There are cases where a setter may be omitted [...]

This has been resolved for Spring Boot 2.2.0, which is supposed to be released soon: https://github.com/spring-projects/spring-boot/issues/8762

Here is how I have it working with my application.yml file.

myconfig:
  my-host: ssl://example.com
  my-port: 23894
  my-user: user
  my-pass: pass

Here is the kotlin file:

@Configuration
@ConfigurationProperties(prefix = "myconfig")
class MqttProperties {
    lateinit var myHost: String
    lateinit var myPort: String
    lateinit var myUser: String
    lateinit var myPass: String    
}

This worked great for me.

With new Spring Boot 2.2 you can do like so:

@ConstructorBinding
@ConfigurationProperties(prefix = "swagger")
data class SwaggerProp(
    val title: String, val description: String, val version: String
)

And don't forget to include this in your dependencies in build.gradle.kts:

dependencies {
  annotationProcessor("org.springframework.boot:spring-boot-configuration-processor")
}