Whats wrong wih this Servlet?

[dineshswamy]

i ve already worked many time on this code ,but couldnt find whats wrong.

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.ServletException;
public class AppletServer extends HttpServlet
{
public void doPost(HttpServletRequest rq, HttpServletResponse rs) throws ServletException,IOException 
{
String s,n,v;
try
{
rs.setContentType("application/x-java-serialized-object");
InputStream i=rq.getInputStream();
ObjectInputStream oi=new ObjectInputStream(i);
OutputStream o=rs.getOutputStream();
ObjectOutputStream oo=new ObjectOutputStream(o);
String l=(String)oi.readObject();
oo.writeObject(l);
oo.flush();
oo.close();
}catch(Exception e){
e.printStackTrace();
}
}
}

actually i m accessing this servlet via an applet and it gives me the following error

java.io.IOException: Server returned HTTP response code: 500 for URL: http://172.16.2.147:8080/cs2k9a23/servlet/hform