public class StartLearningServlet extends BasicServlet {
    public void doExecute(HttpServletRequest req,HttpServletResponse res) 
    	throws ServletException, IOException{
      res.setContentType(getContentType());
      String cmd="";
      PrintWriter out = res.getWriter();
      cmd = req.getParameter("command");
      if (cmd==null)
        result1=stopLearning(userId,password,materialId);
      else
        result1=stopLearning(userId,password,materialId);
      ......//do other operation
    }    
      
    String result1=stopLearning(userId,password,materialId);          
    private String startLearning(String materialId,String userId,
    				String password){
      
    }
    
    private String stopLearning(String materialId,String userId,
    				String password){
      
    }
}