Source - CalculatorServlet.java
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.math.*;
import java.util.*;
import com.cedarspring.tvm.*;
import com.getobjects.bigdecimal.*;
public class CalculatorServlet extends HttpServlet {
public void service (HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
Locale locale = new Locale("en","US");
Hashtable errors = new Hashtable();
/* ------------------------------------------------------------
* Create an instance of the TVM bean
* if one does not already exist in the session and set the locale.
* This bean contains all of the financial calculator logic and
* stores the state (presentValue, futureValue, interestRate,
* etc.) for a particular session.
*
* An instance of the bean will be created for each new session
* and placed in the session scope with a name of "tvm".
* It is initialized with example values. The bean will be
* available to all pages that participate in the session. Any
* property values that are set will persist in the bean for
* the remainder of the session unless they are explicitly
* changed.
*
* A US English locale is established for all pages in the
* session.
* ---------------------------------------------------------- */
HttpSession session = req.getSession(true);
TVMu tvm = (TVMu)session.getAttribute("tvm");
if (tvm == null) {
tvm = new TVMu();
tvm.setLocale(locale);
tvm.setPresentValue(new BigDecimal("200000"));
tvm.setInterestRate(new BigDecimal("7"));
tvm.setNumberOfPeriods(new BigDecimal("360"));
tvm.setPayment(new BigDecimal("-1330.6050"));
session.setAttribute("tvm", tvm);
session.setAttribute("javax.servlet.jsp.jstl.fmt.locale", locale);
}
/* ---------------------------------------------------------------
* Validate the request parameters and set them into the TVM bean.
* The request object, in addition to other useful info, contains
* all the values from our HTML form as sets of name-value pairs.
* They can be retrieved with the getParameter(String name) method
* of the request object.
*
* We will use a BigDecimalFormat object to parse each parameter
* string, to check that it represents a valid decimal number,
* and to create a BigDecimal object from it. The BigDecimal
* result is set into the TVM bean. The bean may do additional
* constraint checking.
*
* If any error occurs, we will write a parameter name - message
* pair into a HashTable that can be forwarded to a JSP page for
* display later.
*
* We will treat empty fields a 0.
*
* The HTML form values may not be present for the very first
* request from a session. We can test for this condition by
* checking if the operation field, which must always be
* present in a valid form, is null.
* ------------------------------------------------------------- */
if (req.getParameter("op") != null) {
BigDecimalFormat bdf = new BigDecimalFormat();
bdf.setLocale(locale);
String msg = "Value is not numeric:";
String err = "";
/*-------------------------------------------
* Present Value
*------------------------------------------- */
String pv = req.getParameter("presentValue");
if (pv.equals("")) {
pv = "0";
}
try {
tvm.setPresentValue(bdf.parse(pv));
} catch (Exception e) {
errors.put("pv", msg);
}
/*-------------------------------------------
* Future Value
*------------------------------------------- */
String fv = req.getParameter("futureValue");
if (fv.equals("")) {
fv = "0";
}
try {
tvm.setFutureValue(bdf.parse(fv));
} catch (Exception e) {
errors.put("fv", msg);
}
/*-------------------------------------------
* Payment
*------------------------------------------- */
String pmt = req.getParameter("payment");
if (pmt.equals("")) {
pmt = "0";
}
try {
tvm.setPayment(bdf.parse(pmt));
} catch (Exception e) {
errors.put("pmt", msg);
}
/*---------------------------------------------------------
* NumberOfPeriods and InterestRate must meet additional
* constraints beyond being a valid number. For example,
* InterestRate cannot be negative. The TVM bean will
* check these constraints when the BigDecimal is set
* into these properties. It will place a text message in
* the message property if the constraint is not satisfied
* rather than throwing an exception. We must check that
* the message property is empty.
* ------------------------------------------------------ */
/*-------------------------------------------
* Number Of Periods
*------------------------------------------- */
String n = req.getParameter("numberOfPeriods");
if (n.equals("")) {
n = "0";
}
try {
tvm.setNumberOfPeriods(bdf.parse(n));
err = tvm.getMessage();
} catch (Exception e) {
err = msg;
}
if (!err.equals("")) {
errors.put("n", err);
err = "";
tvm.clearMessage();
}
/*-------------------------------------------
* Interest Rate
*------------------------------------------- */
String i = req.getParameter("interestRate");
if (i.equals("")) {
i = "0";
}
try {
tvm.setInterestRate(bdf.parse(i));
err = tvm.getMessage();
} catch (Exception e) {
err = msg;
}
if (!err.equals("")) {
errors.put("i", err);
err = "";
tvm.clearMessage();
}
/*----------------------------------------------------
* Perform the calculator command. The "op" request
* parameter contains the operation to preform. Send
* a message to the proper TVM bean method to carry
* out the calculation and store the result.
* ------------------------------------------------- */
String op = req.getParameter("op");
if (op.equals("Present Value"))
tvm.computePresentValue();
else
if (op.equals("Future Value"))
tvm.computeFutureValue();
else
if (op.equals("Periods"))
tvm.computeNumberOfPeriods();
else
if (op.equals("Interest Rate"))
tvm.computeInterestRate();
else
tvm.computePayment();
err = tvm.getMessage();
if (!err.equals("")) {
errors.put("cmp", err);
tvm.clearMessage();
}
}
/*--------------------------------------------------------------
* Dispatcher.
* no errors - forward the request to the calculator form view.
* errors - add the error table to the request and forward
* it to the error form view.
* ----------------------------------------------------------- */
RequestDispatcher rd;
if (errors.isEmpty()) {
rd = getServletContext().getRequestDispatcher("/calculatorForm.jsp");
} else {
req.setAttribute("errors",errors);
rd = getServletContext().getRequestDispatcher("/calculatorErrors.jsp");
}
rd.forward(req, res);
}
}
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