The Java EE 5 Tutorial

Design Strategies

The main job of the JSP pages in the Duke’s Bank application is presentation. They use JavaServer Faces tags to represent UI components on the page, to bind the components to server-side data stored in backing beans, and wire the components to event-handling code. To maintain the separation of presentation and application behavior, most dynamic processing tasks are delegated to enterprise beans, custom tags, and JavaBeans components, including backing beans (see Backing Beans).

In the Duke’s Bank application, the JSP pages rely on backing beans and other JavaBeans components for interactions with the enterprise beans. In the Duke’s Bookstore application, discussed in Chapters Chapter 3, Getting Started with Web Applications to Including the Classes, Pages, and Other Resources, the BookDB JavaBeans component acts as a front end to a database.

In the Duke’s Bank application, CustomerBean acts as a facade to the enterprise beans. Through it, the backing beans can invoke methods on the enterprise beans. For example, TransferFundsBean can indirectly invoke the transferFunds method of the TxControllerBean enterprise bean by first calling getTxController on CustomerBean then calling transferFunds on the TxController interface.

The other backing beans have much richer functionality. ATMBean sets acknowledgment strings according to customer input, and AccountHistoryBean massages the data returned from the enterprise beans in order to present the view of the data required by the customer.

The web client uses a template mechanism implemented by custom tags (discussed in A Template Tag Library) to maintain a common look across all the JSP pages. The template mechanism consists of three components:

Finally, the web client uses logic tags from the JSTL core tag library to perform flow control and tags from the JSTL fmt tag library to localize messages and format currency.