Help with a simple login servlet

Question

I appreciate any help and assistance you all can give. I'm in an Intro to Java class on Georgia State and have an issue with this servlet I'm building. We're developing a login system where we have an http form pass a studentid and pin number to a servlet, then the servlet will match those inputs against the result set from an access database query using sql. I keep getting an error that will be posted below and I can't see any reason why I'd be getting it. Again any help would be appreciated. Here's the info:
import java.io.*;
import java.util.*;
import java.sql.*; // for JDBC
import javax.servlet.*; // for Servlet
import javax.servlet.http.*; // for HttpServlet
public class StudentLogin extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException{
          //get parameters
                    String aStudentId = (String) request.getParameter("studentid");
          String aPin = (String) request.getParameter("pin");
          //define the data source
                    String url = "jdbc:odbc:CIS3270Project";
                    Connection con = null;
                    Statement stmt;
                    String query;
          ResultSet rs = null;
                    //exception handling
                    try {
                    //load the driver -throws ClassNotFoundException
                    Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
                    catch (ClassNotFoundException cnfe) {
                    System.err.println (cnfe);
     try {
                    con = DriverManager.getConnection (url, "my-user", "my-passwd");
                    // create sql statement
                    stmt = con.createStatement ();
                    query = "SELECT * FROM STUDENT WHERE StudentID='" + aStudentId + "'";
                    // run the query
                    rs = stmt.executeQuery (query);
                    //get data from result set
                         rs.next();
                         String studentId = rs.getString("StudentID");
                         String pin = rs.getString("PIN");
                         System.out.println(studentId);
                         System.out.println(pin);
               catch (SQLException ex) {
                    ex.printStackTrace();
response.setContentType("text/html");
PrintWriter out = response.getWriter();
          //compare form data to result set
if(aPin.equals(pin)){
               System.out.println("Login Successful");
          else{
               System.out.println("Login Failed");
The error is as follows:
StudentLogin.java:58: cannot resolve symbol
symbol : variable pin
location: class StudentLogin
if(aPin.equals(pin)){
^
1 error
I've declared pin and there should be no issue with it using it as an argument in this string comparison. Thanks for any light you can shed on this.
-Matt

Answer 1

Alright, I've broken up the code and made it more modular. Here's my code for my Authenticator class followed by the code in the servlet.
import java.sql.*;
import java.io.*;
import java.util.*;
public class Authenticator{
     //define the data source
     Connection con = null;
     Statement stmt;
     String query;
ResultSet rs = null;
     public void loadDb(){
          try {
               //load the driver -throws ClassNotFoundException
               Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
          catch (ClassNotFoundException cnfe) {
               System.err.println (cnfe);
          try {
               con = DriverManager.getConnection ("jdbc:odbc:CIS3270Project", "my-user", "my-passwd");
          catch (SQLException ex) {
               ex.printStackTrace();
     public void queryDb(String aStudentId){
          try {
               // create sql statement
               stmt = con.createStatement ();
               query = "SELECT * FROM STUDENT WHERE StudentID='" + aStudentId + "'";
               // run the query
               rs = stmt.executeQuery (query);
          catch (SQLException xe) {
               xe.printStackTrace();
          try {
               //get data from result set
               rs.next();
               String studentId = rs.getString("StudentId");
               String pin = rs.getString("PIN");
          catch (SQLException x) {
               x.printStackTrace();
     public void isValid(String aPin){
          if(pin.equals(aPin)){
               System.out.println("Login Successful");
          else{
               System.out.println("Login Failed");
Here's the servlet:
import java.io.*;
import java.util.*;
import java.sql.*; // for JDBC
import javax.servlet.*; // for Servlet
import javax.servlet.http.*; // for HttpServlet
public class StudentLogin extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException{
//get parameters
          String aStudentId = (String) request.getParameter("studentid");
String aPin = (String) request.getParameter("pin");
     Authenticator a = new Authenticator();
     a.loadDb();
     a.queryDb(aStudentId);
     a.isValid(aPin);
response.setContentType("text/html");
PrintWriter out = response.getWriter();
//bunch of HTML output shit goes here
I keep getting an error of cannot resolve symbol in the isValid method. It can't resolve the variable 'pin' from the database query. Does try limit the scope of that variable to only inside that try statement? Thanks for any help you guys can give.