AuthorDao.kt

@Repository
class AuthorDao : EntityDao<Author, Int>() {
    override var entity : Class<Author>? = Author::class.java

    fun findByName(
        name : String
    ) : List<Author> {
        val criteriaBuilder = getCriteriaBuilder()
        val criteriaQuery = getCriteriaQuery()
        val root = criteriaQuery.from(entity)

        val query =
            criteriaQuery
                .select(root)
                .where(
                    criteriaBuilder.like(root.get(Author_.name), "%$name%")
                )

        return getQuery(query).resultList
    }
}

EntityDao.kt

@Repository
abstract class EntityDao<T, KEY : Serializable?> {

    @PersistenceContext
    protected lateinit var entityManager: EntityManager

    protected var entity : Class<T>? = null

    fun findByKey(key: KEY): Optional<T> {
        return Optional.of(entityManager.find(entity, key))
    }

    fun findAll(): List<T> {
        val criteriaQuery = getCriteriaQuery()
        val root =  criteriaQuery.from(entity)
        val resultQuery = getQuery(criteriaQuery.select(root))

        return resultQuery.resultList
    }

    fun create(entity: T) : T {
        entityManager.persist(entity)

        return entity
    }

    fun update(entity: T) : T {
        return entityManager.merge(entity)
    }

    fun delete(entity: T) : T {
        entityManager.remove(entity)

        return entity
    }

    protected fun getCriteriaBuilder(): CriteriaBuilder {
        return entityManager.criteriaBuilder
    }

    protected fun getCriteriaQuery(): CriteriaQuery<T> {
        return entityManager.criteriaBuilder.createQuery(entity)
    }

    protected fun getQuery(criteriaQuery : CriteriaQuery<T>): TypedQuery<T> {
        return entityManager.createQuery(criteriaQuery)
    }

}