Question

This is for my Advanced Java Programming class. The book we use is Murach's Java Servlet's and JSP 3rd Edition. I need help modifying some code. I will post the code I was told to open that needs to be modified below.

In this exercise, you'll enhance the Future Value application to store the amount and interest rate in the user's session. That way, the user can experiment with different numbers of years to see the value of his or her investment without having to enter the amount and interest rate each time.

Review the project.

• Start NetBeans and open the project named ch07_ex3_futureValue that's in the more_ex_starts directory.
• Open the index.jsp file. Note the JSTL if tags that display the values of the amount and interest attributes if they are available.
• Open the result.jsp file. Note that a link has been added to take you back to the Calculator page.
• Run the application, enter some values, click the Calculate button, and click the "Return to Calculator" link. On the Calculator page, all of the text boxes should be empty.

Modify the code

• Open the FutureValueServlet class.
• Add code to store the investment amount and interest rate in the user's session. For example, store the investment amount as an attribute named "amount" and the interest rate as an attribute named "interest".
• Run the application again, enter some values, click the Calculate button, and click the "Return to Calculator" link. On the Calculator page, the Investment Amount and Yearly Interest Rate boxes should contain the values you entered.
• Navigate to a different website. Then, return to the Future Value application by entering the following URL in your browser's URL box:

http://localhost:8080/ch07_ex3_futureValue (Links to an external site.)Links to an external site.

Since the values are stored in the session, the application should remember them even though you left the Future Value application and went to a different site.

• Close your browser and restart it. Then, enter the above URL in your browser's URL box again. This time, the application should not remember your values. That's because closing your browser ended your previous session.

Here's the code I was told to open. I think only the FutureValueServlet class needs to be modified. I just need it to meet the requirements above. This is all in Java. Thank you very much.

index.jsp

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@include file="header.jsp" %>
<section>
<h1>Future Value Calculator</h1>
<p><i>${message}</i></p>
<form action="calculate" method="post">
<label>Investment Amount:</label>
<c:if test="${investmentAmount != null}">
<input type="text" name="investment"
value="${investmentAmount}"/><br>
</c:if>
<c:if test="${investmentAmount == null}">
<input type="text" name="investment"
value="${calculation.monthlyInvestmentAmount}"/><br>
</c:if>
<label>Yearly Interest Rate:</label>
<c:if test="${interestRate != null}">
<input type="text" name="interest_rate"
value="${interestRate}"/><br>
</c:if>
<c:if test="${interestRate == null}">
<input type="text" name="interest_rate"
value="${calculation.yearlyInterestRate}"/><br>
</c:if>
<label>Number of Years:</label>
<input type="text" name="years"
value="${calculation.years}"/><br>

<label>&nbsp;</label>
<input type="submit" value="Calculate"/><br>
</form>
</section>
<%@include file="footer.jsp" %>

result.jsp

<%@include file="header.jsp" %>
<section>
<h1>Future Value Calculator</h1>

<label>Investment Amount:</label>
<span>${calculation.monthlyInvestmentAmountCurrencyFormat}</span><br />

<label>Yearly Interest Rate:</label>
<span>${calculation.yearlyInterestRate}</span><br />

<label>Number of Years:</label>
<span>${calculation.years}</span><br />

<label>Future Value:</label>
<span>${calculation.futureValueCurrencyFormat}</span><br />
<label>&nbsp;</label>
<br>
<span><a href="index.jsp">Return to Calculator</a></span>
</section>
<%@include file="footer.jsp" %>

FutureValueServlet.java

package murach.fv;

import java.io.*;
import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;

import murach.business.Calculation;

@WebServlet("/calculate")
public class FutureValueServlet extends HttpServlet {

@Override
protected void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {

// get parameters from the request
String investmentString = request.getParameter("investment");
String interestRateString = request.getParameter("interest_rate");
String yearsString = request.getParameter("years");

// validate the parameters
String url;
String message;
double investment = 0;
double interestRate = 0;
int years = 0;
try {
investment = Double.parseDouble(investmentString);
interestRate = Double.parseDouble(interestRateString);
years = Integer.parseInt(yearsString);
message = "";
url = "/result.jsp";
}
catch (NumberFormatException e) {
message = "Please enter a valid number in all three text boxes.";
url = "/index.jsp";
}

// store data in Calculation object
Calculation calculation = new Calculation();
calculation.setMonthlyInvestmentAmount(investment);
calculation.setYearlyInterestRate(interestRate);
calculation.setYears(years);
  
request.setAttribute("calculation", calculation);
request.setAttribute("message", message);
  
getServletContext()
.getRequestDispatcher(url)
.forward(request, response);
}
  
@Override
protected void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
}

Answer 1

There are two options you can try:

1. Clear up the memory of the current session
// store data in Calculation object
Calculation calculation = new Calculation();
calculation.setMonthlyInvestmentAmount(investment);
calculation.setYearlyInterestRate(interestRate);
calculation.setYears(years);
  
request.setAttribute("calculation", calculation);
request.setAttribute("message", message);
  
getServletContext()
.getRequestDispatcher(url)
.forward(request, response);

HttpSession session = request.getSession(false);
if(session != null) {
//This will clear up the memory of the current session
session.invalidate();
}

2. Delete each attribute of the request

// store data in Calculation object
Calculation calculation = new Calculation();
calculation.setMonthlyInvestmentAmount(investment);
calculation.setYearlyInterestRate(interestRate);
calculation.setYears(years);
  
request.setAttribute("calculation", calculation);
request.setAttribute("message", message);
  
getServletContext()
.getRequestDispatcher(url)
.forward(request, response);

HttpSession session = request.getSession(false);
if(session != null) {
//This will clear up the memory of the current session
session.removeAttribute("calculation");
  session.removeAttribute("message");

}