Create a Kotlin Spring Boot application with PostgreSQL

Learn how to bootstrap a Spring Boot app with Kotlin, PostgreSQL, Hibernate and Flyway

Go to the Spring Initializr website to create a new Spring project with the following dependencies

org.springframework.boot:spring-boot-starter-web
org.springframework.boot:spring-boot-starter-data-jpa
org.postgresql:postgresql
org.flywaydb:flyway-core

Start a local Postgres database

docker run --name postgres -e POSTGRES_PASSWORD=test -p 5432:5432 postgres

Replace application.properties with application.yaml

# Database credentials
spring:
  datasource:
    url: jdbc:postgresql://localhost:5432/
    username: postgres
    password: test
  
# Hibernate logging
logging.level.org.hibernate:
  SQL: DEBUG
  type.descriptor.sql.BasicBinder: TRACE

Create a Flyway migration script in src/resources/db.migration/V1__Create_schema.sql

create table users
(
    id   integer primary key generated always as identity,
    name varchar(100)
);

Create an entity, a repository and a controller

@Entity
@Table(name = "users")
class User(
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY) val id: Long? = null,
    val name: String,
)

@Repository
interface UserRepository : CrudRepository<User, Long> {
}

@RestController
@RequestMapping("user")
class UserController @Autowired constructor(
    val repository: UserRepository,
) {

    @GetMapping("/{id}")
    fun getCurrent(@PathVariable id: Long): User {
        return repository.findById(id).get()
    }

    @GetMapping("create")
    fun create(): String {
        val user = User(null, "peter")
        repository.save(user)
        return "created"
    }
}

Start the application and test it using the above endpoints.