Java™ Application Development on Linux - Dator

416Chapter 18Servlets: Java Pressed into Service18.7DESIGNING A BUDGETPRO SERVLETWhen designing a servlet, there are many different patterns to follow. We can’thope to cover all the approaches that can be used for effective servlet programming.What we hope to do is show you our previous BudgetPro GUI applicationrewritten as a servlet, so that you can see the mechanics of a working servletapplication. From this, you can become accustomed to the mechanics of aservlet so that you’ll feel comfortable with other approaches, too. All servletsneed to use these basic mechanisms.Our BudgetPro GUI application was started from the command line, witha name for the budget and a total dollar amount. We’ll use a static HTML pagewith a form for supplying that information. That will invoke our servlet. Theservlet will use HTML pages analogous to the windows we used in ourGUI—there will be a main screen that shows the current account listing itssubaccounts, and there will also be a screen for creating new subaccounts.One nice feature of HTML-based Web applications is that you can usehyperlinks as a way to both select something and take an action on it. We’ll usethat feature in lieu of a View Subaccount button. Instead of selecting a subaccountand then pressing View Subaccount, the user will only have to click onthe name of the subaccount. As a hyperlink, it will make the request to theservlet to view that subaccount.We will still use a button to send us to the screen for creating the subaccounts.We could have used a hyperlink, but this makes the browser page looka bit more like the GUI version.18.7.1 PrototypeWhen designing servlets, it’s handy to use static HTML pages as a prototypefor the work to be done. You can mock up the various screens using HTML,simulate interactions by using hyperlinks to move between the screens, and geta feel for what the screens and interactions will look like.Such a prototype also serves as a “runnable” specification. It can sometimesbe easier to show the action than to describe it with words. And if you take carewhen you are building these static HTML pages, most of the HTML can bereused directly in the final product. (This will be even more true when we getto JSP.)