Question

I have a html form and I need to get the form data in servlet, then i need to do some mathematical operations with that data. But when I am getting null pointer exception while performing the mathematical operation. I am not able to figure this out. Any help would be appreciated. Thanks.. following is my piece of code.

import java.io.IOException;
import java.io.PrintWriter;
import java.math.BigInteger;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class InterestServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        String amount=request.getParameter("wpamt");
        String time=request.getParameter("prd");
        int amt = Integer.parseInt(amount.trim());
        int period = Integer.parseInt(time.trim());

        int interest=(amt * period)/100;
        out.println("for"+period+"years the interest would be"+interest);
    }
}

Answer 1

String amount=request.getParameter("wpamt");
String time=request.getParameter("prd");
int amt = Integer.parseInt(amount.trim());
int period = Integer.parseInt(time.trim());

If this is where you are getting a NullPointerException (hard to tell without a stack trace and line numbers), one of the parameters is missing (not posted by the client).

If it makes sense to proceed with default values, you can do

int amt = amount != null ? Integer.parseInt(amount.trim()): 100;
int period = period != null ? Integer.parseInt(time.trim()) : 5;

Note that you will also get exceptions if the parameter contains something that is not a number.