The Example Servlets






The Example Servlets

This chapter uses the Duke's Bookstore application to illustrate the tasks involved in programming servlets. Figure 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.

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

Send an acknowledgment of the purchase

ReceiptServlet


The data for the bookstore application is maintained in a database and accessed through the database access class database.BookDBAO. The database package also contains the class Book 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>/javaeetutorial5javaeetutorial5/examples/web/bookstore1/ directory, which is created when you unzip the tutorial bundle (see Building the Examples, page xxxv).

To deploy and run the application using NetBeans 5.5, follow these steps:

1.
Perform all the operations described in Accessing Databases from Web Applications (page 55).

2.
In NetBeans 5.5, select FileOpen Project Folder.

3.
In the Open Project dialog, navigate to:

<INSTALL>/javaeetutorial5/examples/web/

4.
Select the bookstore1 folder.

5.
Select the Open as Main Project checkbox and the Open Required Projects checkbox.

6.
Click Open Project Folder.

7.
In the Projects tab, right-click the bookstore1 project, and select Deploy Project.

8.
To run the application, open the bookstore URL http://localhost:8080/bookstore1/bookstore.

To deploy and run the application using Ant, follow these steps:

1.
In a terminal window, go to <INSTALL>/javaeetutorial5/examples/web/bookstore1/.

2.
Run the command ant. This target will spawn any necessary compilations, copy files to the <INSTALL>/javaeetutorial5/examples/web/bookstore1/build/ directory, and create a WAR file and copy it to the <INSTALL>/javaeetutorial5/examples/web/bookstore1/dist/ directory.

3.
Start the Application Server.

4.
Perform all the operations described in Creating a Data Source in the Application Server (page 56).

5.
To deploy the example, run ant deploy. The deploy target outputs a URL for running the application. Ignore this URL, and instead use the one shown in the next step.

6.
To run the application, open the bookstore URL http://localhost:8080/bookstore1/bookstore.

To learn how to configure the example, refer to the deployment descriptor (the web.xml file), which includes the following configurations:

  • A display-name element that specifies the name that tools use to identify the application.

  • A set of filter elements that identify servlet filters contained in the application.

  • A set of filter-mapping elements that identify which servlets will have their requests or responses filtered by the filters identified by the filter elements. A filter-mapping element can define more than one servlet mapping and more than one URL pattern for a particular filter.

  • A set of servlet elements that identify all the servlet instances of the application.

  • A set of servlet-mapping elements that map the servlets to URL patterns. More than one URL pattern can be defined for a particular servlet.

  • A set of error-page mappings that map exception types to an HTML page, so that the HTML page opens when an exception of that type is thrown by the application.

Troubleshooting

The Duke's Bookstore database access object returns the following exceptions:

  • 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 or the server has not been started or has crashed. You can populate the database by running ant create-tables.

  • 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 you 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.



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