9.8. An Online Store with a Shopping Cart and Session Tracking

This section gives an extended example of how you might build an online store that uses session tracking. The first subsection shows how to build pages that display items for sale. The code for each display page simply lists the page title and the identifiers of the items listed on the page. The actual page is then built automatically by methods in the parent class, based on item descriptions stored in the catalog. The second subsection shows the page that handles the orders. It uses session tracking to associate a shopping cart with each user and permits the user to modify orders for any previously selected item. The third subsection presents the implementation of the shopping cart, the data structures representing individual items and orders, and the catalog.

Creating the Front End

Listing 9.4 presents an abstract base class used as a starting point for servlets that want to display items for sale. It takes the identifiers for the items for sale, looks them up in the catalog, and uses the descriptions and prices found there to present an order page to the user. Listing 9.5 (with the result shown in Figure 9-6) and Listing 9.6 (with the result shown in Figure 9-7) show how easy it is to build actual pages with this parent class.