develop a login page- login servlet - ServletContext

Sun Feb 10, 2013 5:52 am

i m trying to develop a login page and following is the coding of the login servlet but when i try to run this it throws a NullPointerException .i dont know why but this statement ServletContext sc= getServletContext(); is throwing this exception can anyone tell me the reason for this.
thanking u in anticipation
java code

import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class LoginEx extends HttpServlet{
    Connection conn;
    
public void init(ServletConfig s) throws ServletException
{ 
    try
      { 
        
         System.out.println("hello1");
         ServletContext sc=getServletContext();
         System.out.println("hello1");
         String st=sc.getInitParameter("dbclass");

         Class.forName(st);
         conn = DriverManager.getConnection(sc.getInitParameter("dbconn"),sc.getInitParameter("dbuser"),sc.getInitParameter("dbpass"));
    
     }
     catch(Exception cn)
     {
          System.out.println("error"+cn);throw new ServletException();
     }
}
    protected void doPost(HttpServletRequest req,HttpServletResponse resp)throws ServletException,IOException
    {
        
          resp.setContentType("text/html");
          PrintWriter pw = resp.getWriter();
          String n=req.getParameter("name");
          String p=req.getParameter("pass");
     try{
        
          Statement st=conn.createStatement();
          ResultSet rs= st.executeQuery("select * from login where ename="+n+"and pass="+p);
          while(rs.next())
          {
          pw.println("<html><body>welcome</body></html>");
          }
        }
     catch(Exception e){
        System.out.println("error"+e);
    }
     pw.close();
    
    }
    
    
    
}