Using Java and Kotlin Together in Spring Boot & JPA

Inflab is introducing Spring Boot and JPA for its new course editor project, and in the process of choosing a language, decided to use Java and Kotlin together.

Using Java alone has downsides such as the risk of NullPointerException due to the lack of Null safety, and a lack of convenience compared to modern languages, such as no support for default method parameters.

On the other hand, using Kotlin alone causes the following technical mismatch issues.

• Compatibility issues with JPA: Kotlin's philosophy of favoring immutability (final) conflicts with JPA's requirements for mutability (dirty checking, lazy loading).
• Hassle of Setter configuration: In the process of using protected set to protect internal entity properties, the code ends up becoming longer instead.
• Complexity of QueryDSL configuration: (omitted as the text is incomplete)