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210

Chapter 9 Session Tracking

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 upon 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.

DILBERT reprinted by permission of United Syndicate, Inc.

Building the Front End

Listing 9.2 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 9.3 (with the result shown

in Figure 9 3) and Listing 9.4 (with the result shown in Figure 9 4) show

how easy it is to build actual pages with this parent class. 

Listing 9.2 CatalogPage.java 

package coreservlets;

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

import java.util.*;

/** Base class for pages showing catalog entries.

 *  Servlets that extend this class must specify

 *  the catalog entries that they are selling and the page

 *  title before the servlet is ever accessed. This

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.