How to Use Kotlin for Stable Backend Development

KakaoPay uses Kotlin for developing various backend services, including insurance comparison and recommendation and My Car Management services. Through Kotlin, they operate services more robustly and efficiently, and easily build libraries for managing specific domains and write unit tests with clear purposes.

In particular, to ensure data consistency, they recommend creating value validation objects using Value Class. For example, when creating a CarNumber object representing a car number, using a value class reduces overhead in the JVM environment while maintaining object-oriented design.

The key methods for enforcing validation logic during object creation are as follows.

• private constructor: Sets the constructor to private to prevent objects from being created externally without validation.
• invoke operator overloading: Overloads the invoke operator within a companion object, guiding users to naturally use the factory method as if calling a constructor.
• @JsonCreator: Ensures that the intended validation logic is applied during serialization and deserialization via the Jackson library as well.