@Async
public void createCar() {
   final Car car = new Car();
   car.setMarka("Subaru");
   car.setModel("Forester");
   car.setYear();
   //set another data
        
    carRepository.save(car);// carRepository - JpaRepository<Car, Long>
}

public void test() {
   CompletableFuture.supplyAsync(this::createCar).thenAccept(car -> System.out.println("success"));
}

public CompletableFuture<Car> createCar() {
   final Car car = new Car();
   car.setMarka("Subaru");
   car.setModel("Forester");
   car.setYear();
   //set another data

   return CompletableFuture.completedFuture(carRepository.save(car));// carRepository - JpaRepository<Car, Long>
}

public void createCar() {
   final Car car = new Car();
   car.setMarka("Subaru");
   car.setModel("Forester");
   car.setYear();
   //set another data

   CompletableFuture.supplyAsync(() -> carRepository.save(car));// carRepository - JpaRepository<Car, Long>
}

@Bean("threadPoolTaskExecutor")
    public TaskExecutor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(20);
        executor.setMaxPoolSize(1000);
        executor.setWaitForTasksToCompleteOnShutdown(true);
        executor.setThreadNamePrefix("Async-");
        return executor;
    }

@Async("threadPoolTaskExecutor")
....

@Transactional
public <S extends T> S save(S entity) {
  if (this.entityInformation.isNew(entity)) {
     this.em.persist(entity);
     return entity;
  } else {
     return this.em.merge(entity);
  }
}

"Car {id=1,  marka='Subaru', model='Forester',....}"

"Car {id=null,  marka='Subaru', model='Forester',....}"