@RequestMapping("/registrar")
 public ModelAndView initLogin(@ModelAttribute Registro registro, Model model) {
   System.out.println(
       "REGISTRO: " + registro.getUsername() + "      EMAIL: " + registro.getEmail());
   repository.save(new Registro(registro.getUsername(), registro.getEmail()));
   return this.lista(new ModelAndView());
 }
 @RequestMapping("/lista")
 public ModelAndView lista(ModelAndView model) {
   registros = (ArrayList<Registro>) repository.findAll();
   for (Registro registro : registros) {
     System.out.println(
         "USUARIO: " + registro.getUsername() + "      EMAIL: " + registro.getEmail());
   }
   model.setViewName("lista");
   model.addObject("registros", registros);
   return model;
 }