getting response has not been set error on glassfish server console

Question

When i try to run the response.sendRedirect() command in a servlet file i get this error: errorlist

I tried following other examples of codes that do the same thing but i still got the same error so surely im thinking it should be something with the response part that im doing wrong could someone please help me ? I have written the code at the bottom for you guys to see.Thanks guys !

protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException 
     {
     new java.util.Timer().schedule( 
        new java.util.TimerTask() {
            @Override
            public void run() {
                try { 
                    response.sendRedirect("seats.jsp");
                } catch (IOException ex) {
                    Logger.getLogger(config.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }, 
        5000 
     );  
     }