arraylist-java.lang.NumberFormatException: null 求大神！！

java.lang.NumberFormatException: null 求大神！！

教師公寓與教師的關系 程序是想通過教師公寓的id獲取teacher這個集合 比如幾號公寓住著哪些教師 一直報轉換類型錯誤 求大神看看

service裡面的代碼

public static List<Teacher> findTeacher(int id){
    List<Teacher> teacher = new ArrayList<Teacher>();
    SqlSession session =MyBatisUtils.getSqlSession();
    try{
        TeacherApartmentDaoMapper teacherapartmentMapper = session.getMapper(TeacherApartmentDaoMapper.class);
        teacher = teacherapartmentMapper.findTeacher(id);

    }catch(Exception e){
        e.printStackTrace();

    }finally{
        MyBatisUtils.closeSqlSession(session);

    }
    return teacher;

}

Action裡面的代碼

@Action(value="findTeacher")
public void findTeacher()throws Exception{
    ServletActionContext.getResponse().setCharacterEncoding("utf-8");
    List<Teacher> teacher = TeacherApartmentService.findTeacher((Integer.parseInt(ServletActionContext.getRequest().getParameter("ftId"))));// 這裡報錯
    ServletActionContext.getResponse().getWriter()
    .print(new Gson().toJson(teacher));
ServletActionContext.getResponse().getWriter().flush();
ServletActionContext.getResponse().getWriter().close();
}

請問應該怎麼改，這種1對多的關系做起卡了幾天了 求大神指教 感激不盡！！

控制台報的錯是java.lang.NumberFormatException: null

最佳回答：

或者，繼續拆分：

 Var = ServletActionContext.getRequest().getParameter("ftId");   // 不清楚返回的數據類型，請按實現返回的數據類型定義。
 int iFtld = Integer.parseInt(Var);
 List<Teacher> teacher = TeacherApartmentService.findTeacher(iFtld);