springboot 3: ConstructorBinding does not work with kotlin primary constructor

[vinh-hoang]

Version: Springboot 3.0.0 the @ConstructorBinding annotation does not work with the Kotlin primary constructor.
The Annotation is written on the class itself and produces the error "This annotation is not applicable to target 'class'".

[mhalbritter]

This is documented here: https://kotlinlang.org/docs/classes.html#secondary-constructors

If the constructor has annotations or visibility modifiers, the constructor keyword is required and the modifiers go before it:

For example:

@ConfigurationProperties("application")
class CtorBinding @ConstructorBinding constructor(val x: String, val y: String) {
    override fun toString(): String {
        return "CtorBinding(x='$x', y='$y')"
    }
}

[vinh-hoang]

Hi, thanks for the response. In version 2.7.x it works like this (example from baeldung):

@ConfigurationProperties(prefix = "api")
@ConstructorBinding
data class ApiConfiguration(
    val clientId: String,
    val url: String,
    val key: String
)

So I assume this style will not be supported anymore?

[mhalbritter]

This is documented here: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-3.0-Migration-Guide#constructingbinding-no-longer-needed-at-the-type-level

In your case you can drop the @ConstructorBinding because Spring Boot is now clever enough to use the constructor without any annotations.