add.java

public void add(Book book) throws SQLException {
    // Book has no id because we are adding a new one to the database
    PreparedStatement preparedStatement = database.getConnection().prepareStatement("insert into books (id, title, description) values (null, ?, ?)", Statement.RETURN_GENERATED_KEYS);
    preparedStatement.setString(1, book.getTitle());
    preparedStatement.setString(2, book.getDescription());

    preparedStatement.execute();

    // after inserting we want to get the generated id
    ResultSet rs = preparedStatement.getGeneratedKeys();

    if (rs.next()) {
        book.setId(rs.getInt(1));
    }

    preparedStatement.executeUpdate();
}