@Entity
@Getter
@Setter
public class Author implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
....

    @OneToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE}, fetch = FetchType.LAZY, mappedBy = "author")
    private Book book;
}

@Entity
@Getter
@Setter
public class Book implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
...

    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    private Author author;
}

Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
session.persist(author);
session.getTransaction().commit();
session.close();

Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
author.getBook().setAuthor(author);
session.persist(author);
session.getTransaction().commit();
session.close();

<AUTHOR>
    <NAME>Автор 1</NAME>
    <BOOK>
        <NAME>Книга 1</NAME>
    </BOOK>
</AUTHOR>

JAXBContext context = JAXBContext.newInstance(Author.class);
Unmarshaller unmarshaller = context.createUnmarshaller();
Author author = (Author) unmarshaller.unmarshal(new File(fileHeader.getFileName()));

session.persist(author);