@Embeddable
class PostalCode {
    @Column(name="country_code")
    String countryCode;
    @Column(name="zip_code")
    int zipCode;
}

@Embeddable
class TownCode extends PostalCode {
    String town;
}

@Entity
class Town {
    @AttributeOverride(name = "countryCode", column=@Column(name="town_country_code"))
    @AttributeOverride(name = "zipCode", column=@Column(name="town_zip_code"))
    @EmbeddedId
    TownCode townCode;
}