The Example Servlets

Troubleshooting Duke's Bookstore Database Problems

The Example Servlets

This chapter uses the Duke’s Bookstore application to illustrate the tasks involved inprogramming servlets. The source code for the bookstore application is located in thetut-install/javaeetutorial5/examples/web/bookstore1/ directory, which is created when you unzip the tutorial bundle (seeBuilding the Examples).

Table 4-1 lists the servlets that handle each bookstore function. You can find theseservlet classes intut-install/javaeetutorial5/examples/web/bookstore1/src/java/com/sun/bookstore1/. Each programming task is illustrated by one ormore servlets. For example,BookDetailsServlet illustrates how to handle HTTPGET requests,BookDetailsServlet andCatalogServlet show how to construct responses, andCatalogServlet illustrates how to tracksession information.

Table 4-1 Duke’s Bookstore Example Servlets

The data for the bookstore application is maintained in a database and accessedthrough the database access classdatabase.BookDBAO. Thedatabase package also contains the classBook which represents a book. The shopping cart and shopping cart items arerepresented by the classescart.ShoppingCart andcart.ShoppingCartItem, respectively.

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

1. Perform all the operations described inAccessing Databases from Web Applications.

2. In NetBeans IDE, select File→Open Project.

3. In the Open Project dialog, navigate to:

   tut-install/javaeetutorial5/examples/web/

4. Select thebookstore1 folder.

5. Select the Open as Main Project check box and the Open Required Projects check box.

6. Click Open Project.

7. In the Projects tab, right-click thebookstore1 project, and select Undeploy and Deploy.

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

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

1. In a terminal window, go totut-install/javaeetutorial5/examples/web/bookstore1/.

2. Typeant. This command will spawn any necessary compilations, copy files to thetut-install/javaeetutorial5/examples/web/bookstore1/build/ directory, and create a WAR file and copy it to thetut-install/javaeetutorial5/examples/web/bookstore1/dist/ directory.

3. Start the Application Server.

4. Perform all the operations described inCreating a Data Source in the Application Server.

5. To deploy the example, typeant 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 URLhttp://localhost:8080/bookstore1/bookstore.

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

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

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

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

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

• A set ofservlet-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 Duke's Bookstore Database Problems

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 runningant 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 you 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 defaultpage containing the message

A Servlet Exception Has Occurred

and a stack trace that can help you diagnose the cause ofthe exception. If you useerrorpage.html, you will have to look in the serverlog to determine the cause of the exception.

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