How to fix servlet threw exception error

[hellwitu]

I am workin on a mms project and it has the following modules

1. sender and reciever (j2me -using sun wireless toolkit)
2. mm7 and mmsc (java- using eclipse)
3. vasp server and content server (java servelets- using eclipse and tomcat apache)

During normal run the connection should go somewhat like this

sender-->vasp server-->mm7-->mmsc-->reciever-->content server

I have removed all the visible errors. The apache server is up and running, no doubt bout that. I am using port no 80 instead of 8080, so I can enter URLs of the form http://localhost/... instead of http://localhost:8080/....

When i try to run the servelets i get errors such as:

-->The server encountered an internal error () that prevented it from fulfilling this request.
-->SEVERE: Servlet.service() for servlet Vasp_Server threw exception
java.lang.NullPointerException
at Vasp_Server.doGet(Vasp_Server.java:12)

the part of the code that causes this is as below-->

public class Vasp_Server extends HttpServlet
{
    HttpServletResponse res;
    public void doGet( HttpServletRequest req,HttpServletResponse res ) throws IOException, ServletException
    {
        this.res = res;
        String req_msg = req.getParameter( "param" );
(ERROR HERE-->)    req_msg = req_msg.trim();
        if( req_msg.equals( "vasp_msg" ))
        {
            System.out.println("Inside vasp msg provider" );
            vasp_msg_provider();
        } and so on...