AirBookingService.java

class AirBookingService {
    private final Database db;
    private final BookingService bookings;
    private static final Map<String, User> userCache = new HashMap<>();

    public AirBookingService() {
        db = new Database();
        bookings = BookingServiceFactory.getService();
    }

    public Trip bookTicket(long productId, PaymentContext context) {
        final FlightProduct product = getFlightProduct(productId);
        final User user = getUser(context.getUserId());
        final UnbookedTrip unbookedTrip = createTrip(product, user);
        final Trip trip = bookings.bookTrip(unbookedTrip);

        addRewardPointsToUser(trip, user);

        return trip;
    }

    private User getUser(long id) {
        final Connection conn = db.getConnection();

        if (userCache.containsKey(id)) {
            return userCache.get(id);
        }

        try {
            final User user = conn.query("select * from users where id = " + id, new UserMapper());
            user.put(id, user);
            return user;
        } finally {
            conn.close();
        }
    }

    private FlightProduct getFlightProduct(long id) {
        final Connection conn = db.getConnection();
        try {
            return conn.query("select * from products where id = " + id, new FlightProductMapper());
        } finally {
            conn.close();
        }
    }

    private void addRewardPointsToUser(Trip trip, User user) {
        final Connection conn = db.getConnection();
        try {
            conn.query("update users set totalRewardsPoints = totalRewardsPoints + " + trip.getPoints() + " where id = " + user.getId());
        } finally {
            conn.close();
        }
    }

    private UnbookedTrip createTrip(FlightProduct product, User user) {
        // Creates and returns and UnbookedTrip.
    }

}