Nullpointer exception at doGet and doPost methods - servlets

Question

This is the servlet code where I get the Nullpointer exxception.There are no objects that I need to get Initialized. What would be the problem?
package sms.controller;
import sms.model.DbConnection;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import net.sf.json.JSONArray;
import net.sf.json.JSONObject;
public class StaffManagementServlet extends HttpServlet {
Connection con = null;
Statement st = null;
ResultSet rs = null;
PrintWriter out;
JSONArray jsonArray;
JSONObject jsonObject;
private static final long serialVersionUID = 1L;
/**
* #see HttpServlet#HttpServlet()
*/
public StaffManagementServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* #see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doPost(request, response); //line 50
}
/**
* #see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
String action = request.getParameter("action");
System.out.println(action+"--------");
if (action.equalsIgnoreCase("registration")) { //line 63
userRegistration(request, response);
}
if (action.equalsIgnoreCase("login")) {
userLogin(request, response);
}
if (action.equalsIgnoreCase("section")) {
getSection(request, response);
}
if (action.equalsIgnoreCase("question")) {
getQuestion(request, response);
}
if (action.equalsIgnoreCase("semister")) {
getSemister(request, response);
}
if (action.equalsIgnoreCase("branch")) {
getBranch(request, response);
}
if (action.equalsIgnoreCase("forget")) {
forgetPassword(request, response);
}
if (action.equalsIgnoreCase("setPass")) {
setPassword(request, response);
}
}
This is the error I get when I run the sevlet on the server.
java.lang.NullPointerException
sms.controller.StaffManagementServlet.doPost(StaffManagementServlet.java:63)
sms.controller.StaffManagementServlet.doGet(StaffManagementServlet.java:50)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

Answer 1

Your action is NULL so when you call action.equalsIgnoreCase("registration"). It throws NullPointerException.
BEST practice for this case is using CONSTANT as first variable when compare.
if ("registration".equalsIgnoreCase(action)) {
// ....
} else if ("login".equalsIgnoreCase(action)) {
// ....
}
// ....
else {
throw new ServletException("Invalid action");
// OR process default action here if action missing
}

Answer 2

action is null. So calling a method on it throws a NullPointerException. You need to pass an action parameter to your request, or to deal with the possibility of action being null in the doPost() method.