Java™ Application Development on Linux - Dator

18.7 Designing a BudgetPro Servlet41718.7.2 DesignLet’s review what we need our servlet application to do for us. Given an accountname and the initial dollar amount, we need to:• Create a top-level account with that amount of dollars• Display the current account and its total and remaining dollars, along witha list of its subaccounts, if any• Create subaccounts, specifying a name and dollar amount• Make a selected subaccount be the current one, displayed as aboveAfter each or any of these actions, the servlet has to spit out the HTMLpage for the user to view. If the user wants to create a subaccount, then theservlet produces a form page for entering the name and dollar amount for thesubaccount. When the user presses a Create button on that page, the browsertells the servlet (via the form data) that the servlet should create the subaccountand redisplay the current account with this new subaccount added to its list.TIPIt may help to think of the servlet as a two-step process, with a current and futureperspective. The first step is the action that the servlet must perform basedon the supplied parameters (e.g., create a new account). The second step isthe creation of the page allowing the user to take the next (future) action. Thatpage reflects the state of things after the parameter-driven action has occurred.In our example, that means showing the list of subaccounts including the onethat we just created.Let’s spell out in more detail what our interactions with the servlet will be,and describe what output we expect for each of those inputs. We will create akeyword to tell the servlet what function we want it to perform; we’ll call theparameter func. We will sometimes need two other parameters: name anddollars.Table 18.1 shows our design as a compact reference.The code for our servlet is at http://www.javalinuxbook.com/. Let’slook at some of the key parts of the servlet in more detail. We’ll look at:1) reading the parameters, 2) the core business logic of the servlet, as describedin Table 18.1, and 3) how we create and output the HTML.