@RequestMapping("session/modify")
  public String modify(HttpSession session) {
    student.setName("이승수12");
    student.setAvg(77);

    session.setAttribute("id", student);
    return "sessionView";
  }
  @RequestMapping("session/make")
  public String make(HttpSession session) {
    student.setName("이승수");
    student.setAvg(88);

    session.setAttribute("id", student);
    return "sessionView";
  }