public Result listarAlumnos() {
    Result res;

    List<Alumno> alumnos = Alumno.findAll();

    if (ControllerHelper.acceptsJson(request())) {
      res = ok(Json.toJson(alumnos));
    } else if (ControllerHelper.acceptsXml(request())) {
      res = ok(views.xml.alumnos.render(alumnos));
    } else {
      res = badRequest(ControllerHelper.errorJson(1, "unsupported_format", null));
    }

    return res;
  }
  // {"id":"12345678", "nombre":"aaaa", "apellido1":"bbbb", "apellido2":"ccccc"}
  public Result getAlumno(String id) {
    Result res;

    Alumno alumno = Alumno.find.byId(id);

    if (alumno == null) {
      res = notFound();
    } else {
      if (ControllerHelper.acceptsJson(request())) {
        res = ok(Json.toJson(alumno));
      } else if (ControllerHelper.acceptsXml(request())) {
        res = ok(views.xml.alumno.render(alumno));
      } else {
        res = badRequest(ControllerHelper.errorJson(1, "unsupported_format", null));
      }
    }

    return res;
  }