Develop a Loan Calculator Program in Servlet

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.text.*;
public class RegPayS extends HttpServlet {
double principal;
double intRate;
double numYears;
final int payPerYear = 12;
NumberFormat nf;
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
String payStr = "";
nf = NumberFormat.getInstance();
nf.setMinimumFractionDigits(2);
nf.setMaximumFractionDigits(2);
String amountStr = request.getParameter("amount");
String periodStr = request.getParameter("period");
String rateStr = request.getParameter("rate");
try {
if(amountStr != null && periodStr != null &&
rateStr != null) {
principal = Double.parseDouble(amountStr);
numYears = Double.parseDouble(periodStr);
intRate = Double.parseDouble(rateStr) / 100;
payStr = nf.format(compute());
}
else {
amountStr = "";
periodStr = "";
rateStr = "";
}
} catch (NumberFormatException exc) {
// Take appropriate action here.
}

response.setContentType("text/html");

PrintWriter pw = response.getWriter();

pw.print("" +
"

" +
"Enter amount to finance:" +
" ");
pw.print("
Enter term in years:" +
" ");
pw.print("
Enter interest rate:" +
" ");
pw.print("
Monthly Payment:" +
" ");
pw.print("
");
pw.println("

");
}

double compute() {
double numer;
double denom;
double b, e;
numer = intRate * principal / payPerYear;
e = -(payPerYear * numYears);
b = (intRate / payPerYear) + 1.0;
denom = 1.0 - Math.pow(b, e);
return numer / denom;
}
}