Issue
I am writing a servlet calculator using doPost method of servlet container.
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//show result page
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>SIMPLE CALCULATOR<br><br><br></head>");
out.println("<body>");
out.println("<form method = 'post' action = 'calc'>");
out.println("enter the first number:<br>");
out.println("<input type = 'text' name='number1'><br><br>");
out.println("enter the second number:<br>");
out.println("<input type = 'text' name='number2'><br><br>");
out.println("enter the operation:<br><br>");
out.println("<input type ='radio' name = 'op' value = '+'>add<br>");
out.println("<input type = 'radio' name = 'op' value = '-'>sub<br>");
out.println("<input type = 'radio' name = 'op' value = '*'>mul<br>");
out.println("<input type = 'radio' name = 'op' value = '/'>div<br><br>");
out.println("<input type = 'submit' name = 'result' value = 'submit'><br>");
out.println("</body>");
out.println("</html>");
int a1= Integer.parseInt(request.getParameter("number1"));
int a2= Integer.parseInt(request.getParameter("number2"));
String operation = request.getParameter("op");
int result = 0;
if(operation.equals("+"))
{
result = a1 + a2;
out.println("The result of " + a1 + " " + operation + " "+ a2 + " = "+ result);
}
if(operation.equals("-"))
{
result = a1 - a2;
out.println("The result of " + a1 + " " + operation + " " + a2 + " = "+ result);
}
if(operation.equals("*"))
{
result = a1 * a2;
out.println("The result of " + a1 + " " + operation + " " + a2 + " = "+ result);
}if(operation.equals("/"))
{
result = a1 / a2;
out.println("The result of " + a1 + operation + a2 + " = "+ result);
}
out.println("<table border=1>");
out.println("<tr>");
out.println("<th>first</th>");
out.println("<th>operation</th>");
out.println("<th>second</th>");
out.println("<th>result</th>");
out.println("</tr>");
out.println("<tr>");
out.println("<td>" + a1 + "</td>");
out.println("<td>" + operation + "</td>");
out.println("<td>" + a2 + "</td>");
out.println("<td>" + result + "</td>");
out.println("</tr>");
out.println("</table>");
out.flush();
}
I wanted to display the values and operations and results everytime I do calculation and click the submit button. What I am now seeing is that only the first calculation values are displayed and when I do the second one It changes the previous one and displays itself.
Expected output is
I am now seeing
Anyone has any help?
Solution
My solution would be to use a list of strings to store the history. If you want a better solution, you could write a class that has first, second, and operator so that you can retrieve each property. I store the list in the session so that it can be accessed by the JSP page. I'm just writing a minimal solution. It's up to you to rewrite it to meet your requirements.
JSP page
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<form action="ComputeServlet" method="post">
<input type="text" name="firstNumber" size="5">
<select name="operator">
<option value="+">+</option>
<option value="+">-</option>
<option value="+">*</option>
<option value="+">/</option>
</select>
<input type="text" name="secondNumber" size="5">
<input type="submit" name="submit" value="submit">
<c:forEach var="problem" items="${history}">
<p>${problem}</p>
</c:forEach>
<input type="submit" name="clear" value="clear">
</form>
Servlet
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
if (request.getParameter("clear")!=null){
List<String> history = (List<String>) request.getSession().getAttribute("history");
if (history == null){
history = new ArrayList<>();
request.getSession().setAttribute("history", history);
} else {
history.clear();
}
} else if (request.getParameter("submit")!=null){
int first = Integer.parseInt(request.getParameter("firstNumber"));
int second = Integer.parseInt(request.getParameter("secondNumber"));
String op = request.getParameter("operator");
int result = 0;
switch(op){
case "+": result = first+second; break;
case "*": result = first*second; break;
case "/": result = first/second; break;
case "-": result = first-second; break;
}
List<String> history = (List<String>) request.getSession().getAttribute("history");
if (history == null){
history = new ArrayList<>();
request.getSession().setAttribute("history", history);
}
history.add("" + first + op + second + "=" + result);
}
getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
}
Output
<form action="ComputeServlet" method="post">
<input type="text" name="firstNumber" size="5">
<select name="operator">
<option value="+">+</option>
<option value="+">-</option>
<option value="+">*</option>
<option value="+">/</option>
</select>
<input type="text" name="secondNumber" size="5">
<input type="submit" name="submit" value="submit">
<p>4+5=9</p>
<p>2+6=8</p>
<p>3+2=5</p>
<p>3+2=5</p>
<input type="submit" name="clear" value="clear">
</form>
Answered By - Cheng Thao
Answer Checked By - Robin (JavaFixing Admin)
