Validation in service Layer with Spring MVC

Question

I would like to know how to perform a clean code to organize validation in my service layer.

So, I have this service:

public interface PersonService {

        public Person getPerson(int idperson);   
        public List   getPeopleWithFather( int idFather); 
}

For the validation of the service layer I use Spring AOP (Aspectj), so for validate the first method :

 public Person getPerson(int idperson){
     return personRepository.getPerson(idperson);
 }


@AfterReturning( 
            pointcut="execution(* business.PersonService.getPerson(..))",
            returning = "result")
    public void afterRunning(JoinPoint joinPoint, Object result){
        Person person = (Person) result;       
        if(person == null){
            throw new PersonNotFound();
        }
    }

So in my service, I dont need to write try/catch or maybe conditions of validate. But, I don't know how I can organize my code for the second method, because :

1. First, I need to validate that the father exists with his id.
2. get list of children.

One way is to do so:

public List   getPeopleWithFather( int idFather){
    Person father = getPerson(idFather);
    if(father != null){ return personRepository.getPeopleWithFather(father);  }
    return null;
}

Other way is :

    public List   getPeopleWithFather( int idFather){
        Person father = ((PersonService) AopContext.currentProxy() ).getPerson(idFather);
        return personRepository.getPeopleWithFather(father);
    }

@AfterThrowing(pointcut="execution(* business.PersonService.getPeopleWithFather(..))",
            throwing = "throwable")
    public void afterThrowing(JoinPoint joinPoint, Exception throwable){
        if( throwable instanceof PersonNotFound){
           throw  new PersonNotFound("whatever");
        }
    }

There a more elegant way to perform these validations?. Thanks in advance.