MultipleJoinsQuery.java

// initializing the CriteriaBuilder and CriteriaQuery object
CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
// if you want to perform a multiselect() you need define
// a CriteriaQuery with the Tuple type 
CriteriaQuery<Tuple> criteriaQuery = criteriaBuilder.createQuery(Tuple.class);

Root<Book> root = criteriaQuery.from(Book.class);
// defining the JOIN clauses
Join<Book, Author> author = root.join("authors");
Join<Book, Genre> genre = root.join("genres");

// defining the multi SELECT clause and 
// specifying the WHERE conditions
criteriaQuery
             .multiselect(root, genre)
             .where(
                criteriaBuilder.equal(author.get("id"), 3),
                criteriaBuilder.equal(genre.get("id"), 5)
);

// retrieving the list of <Book, Genre> tuples
List<Tuple> bookGenreTuples = entityManager
                                          .createQuery(criteriaQuery)
                                          .getResultList();