edit: delete repository methods in  already implemented by JpaRepository

@Repository

public interface UserRepository extends JpaRepository<User, Long> {

    @Query("SELECT u FROM User u WHERE u.id = :id")

    Optional<User> findById(@Param("id") Long id);

    @Query("SELECT u FROM User u WHERE u.username = :username")

    Optional<User> findByUsername(@Param("username") String username);