How does this example work even if no oracle to be used and only access is available?

CONNECTION CLASS

package ExamplePackage;

import java.sql.*; import java.util.*;

public class ConnectionManager {

  static Connection con;
  static String url;

  public static Connection getConnection()
  {

     try
     {

        Class.forName("oracle.jdbc.driver.OracleDriver");
        System.out.println(" Defing the URL");

         String url= "jdbc:oracle:thin:@172.24.137.30:1521:ORA10G";
        // assuming "DataSource" is your DataSource name

       // Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

        try
        {   


            System.out.println(" Defing the username");
            String username= ""; 
            System.out.println(" Defing the password");
            String password= "";
            System.out.println(" Defing the connection");
            con = DriverManager.getConnection(url,username,password); 
            System.out.println(" connection done" +con);





        }

        catch (SQLException ex)
        {
           ex.printStackTrace();
        }
     }

     catch(ClassNotFoundException e)
     {
        System.out.println(e);
     }

  return con;

} }

LOGIN SERVLET

package ExamplePackage;

import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession;

/** * Servlet implementation class LoginServlet */ public class LoginServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, java.io.IOException {

try {

 UserBean user = new UserBean();
 user.setUserName(request.getParameter("un"));
 user.setPassword(request.getParameter("pw"));

 user = UserDAO.login(user);

 if (user.isValid())
 {

      HttpSession session = request.getSession(true);       
      session.setAttribute("currentSessionUser",user); 
      response.sendRedirect("userLogged.jsp"); //logged-in page             
 }

 else 
      response.sendRedirect("invalidLogin.jsp"); //error page

}

catch (Throwable theException)
{ System.out.println(theException); } } }

USERBEAN

package ExamplePackage;

public class UserBean {

  private String username;
  private String password;
  private String firstName;
  private String lastName;
  public boolean valid;


  public String getFirstName() {
     return firstName;
}

  public void setFirstName(String newFirstName) {
     firstName = newFirstName;
}


  public String getLastName() {
     return lastName;
        }

  public void setLastName(String newLastName) {
     lastName = newLastName;
        }


  public String getPassword() {
     return password;
}

  public void setPassword(String newPassword) {
     password = newPassword;
}


  public String getUsername() {
     return username;
        }

  public void setUserName(String newUsername) {
     username = newUsername;
        }


  public boolean isValid() {
     return valid;
}

  public void setValid(boolean newValid) {
     valid = newValid;
}

}

USERDAO package ExamplePackage;

import java.text.*; import java.util.*; import java.sql.*;

public class UserDAO
{ static Connection currentCon = null; static ResultSet rs = null;

  public static UserBean login(UserBean bean) {

     //preparing some objects for connection 
     Statement stmt = null;    

     String username = bean.getUsername();    
     String password = bean.getPassword();   

     String searchQuery =
           "select * from users where username='"
                    + username
                    + "' AND password='"
                    + password
                    + "'";

  // "System.out.println" prints in the console; Normally used to trace the process
  System.out.println("Your user name is " + username);          
  System.out.println("Your password is " + password);
  System.out.println("Query: "+searchQuery);

  try 
  {
     //connect to DB 
     currentCon = ConnectionManager.getConnection();
     stmt=currentCon.createStatement();
     rs = stmt.executeQuery(searchQuery);           
     boolean more = rs.next();

     // if user does not exist set the isValid variable to false
     if (!more) 
     {
        System.out.println("Sorry, you are not a registered user! Please sign up first");
        bean.setValid(false);
     } 

     //if user exists set the isValid variable to true
     else if (more) 
     {
        String firstName = rs.getString("firstname");
        String lastName = rs.getString("lastname");

        System.out.println("Welcome " + firstName);
        bean.setFirstName(firstName);
        bean.setLastName(lastName);
        bean.setValid(true);
     }
  } 

  catch (Exception ex) 
  {
     System.out.println("Log In failed: An Exception has occurred! " + ex);
  } 

  //some exception handling
  finally 
  {
     if (rs != null)    {
        try {
           rs.close();
        } catch (Exception e) {}
           rs = null;
        }

     if (stmt != null) {
        try {
           stmt.close();
        } catch (Exception e) {}
           stmt = null;
        }

     if (currentCon != null) {
        try {
           currentCon.close();
        } catch (Exception e) {
        }

        currentCon = null;
     }
  }

return bean;

  }

}