Does the rowMappper in spring work for assigning a row to another object?

I have a DAO in my spring project which gets two variables from other tables. I want to fetch a row by ID in this DAO and I want to have those two variables as objects in return. I wrote the DAO class and my rowMapper class as below. But I can not get the author and publisher objects. I am getting nullPointerException. How should I get those objects in my book object(my author and publisher DAO work fine.)?

public class BookDAO extends JdbcDaoSupport {
public Book getBookById(int bookId) throws SQLException,
        ClassNotFoundException {
    String sql = "select * from library.tbl_book where bookId = ?";
    return this.getJdbcTemplate().queryForObject(sql,new Object[] { bookId }, new BookMapper());
}


private static final class BookMapper implements RowMapper<Book> {

    @Override
    public Book mapRow(ResultSet rs, int rowNum) {
        Book book = new Book();
        Author author = new Author();
        Publisher publisher = new Publisher();
        AuthorDAO authorDAO = new AuthorDAO();
        PublisherDAO publisherDAO = new PublisherDAO();

        try {
            book.setBookId(rs.getInt("bookId"));
            book.setTitle(rs.getString("title"));
            author = authorDAO.getAuthorById(rs.getInt("authId"));
            book.setAuthor(author);
            publisher = publisherDAO.getPublisherById(rs.getInt("pubId"));
            book.setPublisher(publisher);

        } catch (ClassNotFoundException | SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return book;
    }