The Example JSP Pages

The Example JSP Pages

To illustrate JSP technology, this chapter rewrites each servlet in the Duke’s Bookstoreapplication introduced inThe Example Servlets as a JSP page (seeTable 5-1).

Table 5-1 Duke’s Bookstore Example JSP Pages

The data for the bookstore application is still maintained in a database andis accessed throughtut-install/javaeetutorial5/examples/web/bookstore2/src/java/com/sun/bookstore2/database/BookDBAO.java. However, the JSP pages accessBookDBAO through the JavaBeanscomponenttut-install/javaeetutorial5/examples/web/bookstore2/src/java/com/sun/bookstore2/database/BookDB.java. This class allows the JSP pages to use JSP elementsdesigned to work with JavaBeans components (seeJavaBeans Component Design Conventions).

The implementation of the database bean follows. The bean has two instance variables:the current book and the data access object.

package database;public class BookDB {    private String bookId = "0";    private BookDBAO database = null;    public BookDB () throws Exception {    }    public void setBookId(String bookId) {        this.bookId = bookId;    }    public void setDatabase(BookDAO database) {        this.database = database;    }    public Book getBook()         throws Exception {        return (Book)database.getBook(bookId);    }    ...}

This version of the Duke’s Bookstore application is organized along the Model-View-Controller (MVC)architecture. The MVC architecture is a widely used architectural approach for interactive applicationsthat distributes functionality among application objects so as to minimize the degree ofcoupling between the objects. To achieve this, it divides applications into three layers: model,view, and controller. Each layer handles specific tasks and has responsibilities to theother layers:

• Themodel represents business data, along with business logic or operations that govern access and modification of this business data. The model notifies views when it changes and lets the view query the model about its state. It also lets the controller access application functionality encapsulated by the model. In the Duke’s Bookstore application, the shopping cart and database access object contain the business logic for the application.

• Theview renders the contents of a model. It gets data from the model and specifies how that data should be presented. It updates data presentation when the model changes. A view also forwards user input to a controller. The Duke’s Bookstore JSP pages format the data stored in the session-scoped shopping cart and the page-scoped database bean.

• Thecontroller defines application behavior. It dispatches user requests and selects views for presentation. It interprets user inputs and maps them into actions to be performed by the model. In a web application, user inputs are HTTPGET andPOST requests. A controller selects the next view to display based on the user interactions and the outcome of the model operations. In the Duke’s Bookstore application, theDispatcher servlet is the controller. It examines the request URL, creates and initializes a session-scoped JavaBeans component (the shopping cart), and dispatches requests to view JSP pages.

Note -When employed in a web application, the MVC architecture is often referred toas a Model-2 architecture. The bookstore example discussed inChapter 4, Java Servlet Technology, which intermixes presentationand business logic, follows what is known as a Model-1 architecture. The Model-2architecture is the recommended approach to designing web applications.

In addition, this version of the application uses several custom tags from theJavaServer Pages Standard Tag Library (JSTL), described inChapter 7, JavaServer Pages Standard Tag Library:

• c:if,c:choose,c:when, andc:otherwise for flow control

• c:set for setting scoped variables

• c:url for encoding URLs

• fmt:message,fmt:formatNumber, andfmt:formatDate for providing locale-sensitive messages, numbers, and dates

Custom tags are the preferred mechanism for performing a wide variety of dynamicprocessing tasks, including accessing databases, using enterprise services such as email and directories,and implementing flow control. In earlier versions of JSP technology, such tasks wereperformed with JavaBeans components in conjunction with scripting elements (discussed inChapter 9, Scripting in JSP Pages). Although stillavailable in JSP 2.0 technology, scripting elements tend to make JSP pages moredifficult to maintain because they mix presentation and logic, something that is discouragedin page design. Custom tags are introduced inUsing Custom Tags and described indetail inChapter 8, Custom Tags in JSP Pages.

Finally, this version of the example contains an applet to generate a dynamicdigital clock in the banner. SeeIncluding an Applet for a description of theJSP element that generates HTML for downloading the applet.

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 thebookstore2 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 thebookstore2 project, and select Undeploy and Deploy.

8. To run the application, open the bookstore URLhttp://localhost:8080/bookstore2/books/bookstore.

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

1. In a terminal window, go totut-install/javaeetutorial5/examples/web/bookstore2/.

2. Typeant. This command will spawn any necessary compilations, copy files to thetut-install/javaeetutorial5/examples/web/bookstore2/build/ directory, and create a WAR file and copy it to thetut-install/javaeetutorial5/examples/web/bookstore2/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/bookstore2/books/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.

• Acontext-param element that specifies the JSTL resource bundle base name.

• Alistener element that identifies theContextListener class used to create and remove the database access.

• Aservlet element that identifies theDispatcher servlet instance.

• A set ofservlet-mapping elements that mapDispatcher to URL patterns for each of the JSP pages in the application.

• Nested inside ajsp-config element are twojsp-property-group elements, which define the preludes and coda to be included in each page. SeeSetting Properties for Groups of JSP Pages for more information.

Figure 5-2 shows thebookcatalog.jsp page from the Duke’s Bookstore application. This page displaysa list of all the books that are available for purchase.

Figure 5-2 Book Catalog

SeeTroubleshooting Duke's Bookstore Database Problems for help with diagnosing common problems related to the database server.If the messages in your pages appear as strings of the form???Key???, the likely cause is that you have not provided thecorrect resource bundle base name as a context parameter.

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