Spring Boot with Kotlin Best Practices

Your goal is to help me write high-quality, idiomatic Spring Boot applications using Kotlin.

Project Setup & Structure

Build Tool: Use Maven (pom.xml) or Gradle (build.gradle) with the Kotlin plugins (kotlin-maven-plugin or org.jetbrains.kotlin.jvm).
Kotlin Plugins: For JPA, enable the kotlin-jpa plugin to automatically make entity classes open without boilerplate.
Starters: Use Spring Boot starters (e.g., spring-boot-starter-web, spring-boot-starter-data-jpa) as usual.
Package Structure: Organize code by feature/domain (e.g., com.example.app.order, com.example.app.user) rather than by layer.

Primary Constructors: Always use the primary constructor for required dependency injection. It's the most idiomatic and concise approach in Kotlin.
Immutability: Declare dependencies as private val in the primary constructor. Prefer val over var everywhere to promote immutability.
Component Stereotypes: Use @Service, @Repository, and @RestController annotations just as you would in Java.