Home TOC

The Example Servlets

This chapter uses the Duke's Bookstore application to illustrate the tasks involved in programming servlets. Table 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 shows you how to track session information.

Table 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.

The source for the bookstore application is located in the docs/tutorial/examples/web/bookstore1 directory created when you unzip the tutorial bundle (see Running the Examples). To build, deploy, and run the example:

1. Go to the examples directory and build and deploy the example by running ant. This runs the default ant target deploy which depends on the build target. The build target will spawn any necessary compilations and copy files to the docs/tutorial/examples/web/bookstore1/build directory. The deploy target copies the bookstore1 context file to <JWSDP_HOME>/webapps as described in Running Web Applications.
1. Start the Pointbase database server (see Accessing Databases from Web Applications).
2. Start or restart Tomcat.
3. Open the bookstore URL http://localhost:8080/bookstore1/enter.

Troubleshooting

Common Problems and Their Solutions lists some reasons why a Web client can fail. In addition, Duke's Bookstore returns the following exceptions:

• BookNotFoundException--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-web-db or if the database server hasn't been started or it has crashed.
• BooksNotFoundException--if the bookstore data can't be retrieved. This will occur if you haven't loaded the bookstore database with data by running ant create-web-db or if the database server hasn't been started or it has crashed.
• UnavailableException--if a servlet can't retrieve the Web context attribute representing the bookstore. This will occur if you haven't copied the Pointbase client library <PB_HOME>/client/lib/pbclient41ev.jar to <JWSDP_HOME>/common/lib.

Since 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 the errorpage.html, you will have to look in the Web container's 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.

Home TOC