Access all field of a generic class

I'm using spring data.

I'm trying to do a generic search who will add all field of the class in specification

public abstract class BaseRepository<T, R> extends SimpleJpaRepository implements IBaseRepository<T, R> {
    @PersistenceContext
    private EntityManager em;

    @Autowired
    public BaseRepository(Class<T> domainClass, EntityManager em) {
        super(domainClass, em);

    }

     @Override
    public Page<T> advancedSearch(R r, Pageable page) {
        Specification<T> specification = (Root<T> root, CriteriaQuery<?> cq, CriteriaBuilder cb) -> {

            Predicate p = cb.conjunction();                
           //how to access field of T
            return p;
        };
        return this.findAll(specification, page);
    }
}

How can I access field of T?