The Example Servlets

This chapter uses the Duke's Bookstore application to illustrate the tasks involved in programming servlets. Table 15-1 lists the servlets that handle each bookstore function. Each programming task is illustrated by one or more servlets. For example, BookDetailsServlet illustrates how to handle HTTP GET requests, BookDetailsServlet and CatalogServlet show how to construct responses, and CatalogServlet illustrates how to track session information.

Table 15-1 Duke's Bookstore Example Servlets
Function	Servlet
Enter the bookstore	`BookStoreServlet`
Create the bookstore banner	`BannerServlet`
Browse the bookstore catalog	`CatalogServlet`
Put a book in a shopping cart	`CatalogServlet`, `BookDetailsServlet`
Get detailed information on a specific book	`BookDetailsServlet`
Display the shopping cart	`ShowCartServlet`
Remove one or more books from the shopping cart	`ShowCartServlet`
Buy the books in the shopping cart	`CashierServlet`
Receive an acknowledgement for the purchase	`ReceiptServlet`

The data for the bookstore application is maintained in a database and accessed through the helper class database.BookDB. The database package also contains the class BookDetails, which represents a book. The shopping cart and shopping cart items are represented by the classes cart.ShoppingCart and cart.ShoppingCartItem, respectively.

The source code for the bookstore application is located in the <INSTALL>/jwstutorial12/examples/web/bookstore1/ directory created when you unzip the tutorial bundle (see Building and Running the Examples). A sample bookstore1.war is provided in <INSTALL>/jwstutorial12/examples/web/provided-wars/. To build, package, deploy, and run the example:

Build and package the bookstore common files as described in Updating Web Applications.

In a terminal window, go to <INSTALL>/jwstutorial12/examples/web/bookstore1/.

Run ant build. This target will spawn any necessary compilations and copy files to the <INSTALL>/jwstutorial12/examples/web/bookstore1/build/ directory.

Start Tomcat.

Perform all the operations described in Accessing Databases from Web Applications.

Run ant install-config. The install-config target notifies Tomcat that the new context is available.

To run the application, open the bookstore URL http://localhost:8080/bookstore1/bookstore.

Run ant package. The package task creates a WAR file containing the application classes in WEB-INF/classes and the context.xml file in META-INF.

Run ant deploy. The deploy target copies the WAR to Tomcat and notifies Tomcat that the new context is available.

Troubleshooting

BookNotFoundException--Returned if a book can't be located in the bookstore database. This will occur if you haven't loaded the bookstore database with data by running ant create-book-db or if the database server hasn't been started or it has crashed.

BooksNotFoundException--Returned if the bookstore data can't be retrieved. This will occur if you haven't loaded the bookstore database with data or if the database server hasn't been started or it has crashed.

UnavailableException--Returned if a servlet can't retrieve the Web context attribute representing the bookstore. This will occur if the database server hasn't been started.

Because we have specified an error page, you will see the message The application is unavailable. Please try later. If you don't specify an error page, the Web container generates a default page containing the message A Servlet Exception Has Occurred and a stack trace that can help diagnose the cause of the exception. If you use errorpage.html, you will have to look in the server log to determine the cause of the exception. Web log files reside in the directory <JWSDP_HOME>/logs and are named jwsdp_log.<date>.txt.