Handling Regular Expressions with JPA Criteria API

Question

Is it possible to implement Pattern querying with JPA Criteria API?

In my case, regex patterns are stored into a quick bag property; and I'm trying to avoid using native queries (e.g. PostgreSQL POSIX support).

@Entity @Table(name = "rcp")
public class Recipient {    
    @Id @Column(name = "rcp_email_id")
    @Email
    private String email;
    @CollectionTable(joinColumns = @JoinColumn(name = "rcp_email_fk"))
    @ElementCollection(fetch = EAGER)
    @Convert(converter = PatternConverter.class)
    private Set<Pattern> rules = new HashSet<>();
    ...
}

So I figured I could use the Criteria API but failed to properly develop the technlogy, obviously:

@AllArgsConstructor
public class RecipientSpecification implements Specification<Recipient> {
    private String sample;
    @Override
    public Predicate toPredicate(Root<Recipient> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
        return builder.exists(root.join("rules").as(Pattern.class).matcher(sample).find());
    }
}

I thought I could work on the join with a cast and execute the Java Pattern logic by casting the properties, which I realize to be dumb now because it has no sense from the JPA DSL point of view. It doesn't even compile! But is there a proper way to proceed?

Thanks in advance