Kotlin Spring boot #ConfigurationProperties for list - spring

Question

I want to read the yaml config files using Kotlin and below is my code:
application.yml
message:
messages:
- name: abc
type: aaa
size: 10
- name: xyz
type: bbb
size: 20
MessageConfig.kt
package com.example.demokotlin
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.context.annotation.Configuration
import java.math.BigDecimal
#ConfigurationProperties(prefix = "message")
#Configuration
class MessageConfig {
lateinit var messages: List<Message>
}
class Message {
lateinit var name: String
lateinit var type: String
lateinit var size: BigDecimal
}
Class to use the config:
package com.example.demokotlin
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.stereotype.Component
#Component
class MessageService #Autowired constructor(private var messageConfig: MessageConfig) {
fun createMessage(): String {
println("in service........")
println(messageConfig.messages[0].name)
println(messageConfig.messages[0].type)
println(messageConfig.messages[0].size)
return "create a message......."
}
}
Looks like if the yaml file has array/list, Kotlin can't read it properly but it works without array.
I have exactly the same code and works for Java. Something wrong with my Kotlin code?

Answer 1

You are encountering this bug. Simply changing
lateinit var messages: List<Message>
to
var messages: MutableList<Message> = mutableListOf()
makes your code work. Here is a full working example.
edit (March 2019):
As of SB 2.0.0.RC1 and Kotlin 1.2.20, you can use lateinit or a nullable var.
Docs
edit (May 2020):
As of SB 2.2.0 you can use #ConstructorBinding along with #ConfigurationProperties to set val properties on a data class.
Using the original class as an example, you can now write it like so:
#ConstructorBinding
#ConfigurationProperties(prefix = "message")
data class MessageConfig(val messages: List<Message>) {
data class Message(
val name: String,
val type: String,
val size: BigDecimal
)
}

Answer 2

Is Fixed in Kotlin 1.3.11 with spring-boot 2.10, sample provided in MessageConfig.kt works now
#PropertySource("classpath:application.yml")
#ConfigurationProperties(value = "message")
class MessageConfig {
lateinit var messages: List<Message>
}
class Message {
lateinit var name: String
lateinit var type: String
lateinit var size: BigDecimal
}