java.lang.NumberFormatException: null 求大神！！

Question

教师公寓与教师的关系 程序是想通过教师公寓的id获取teacher这个集合 比如几号公寓住着哪些教师 一直报转换类型错误 求大神看看

service里面的代码

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里面的代码

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

请问应该怎么改，这种1对多的关系做起卡了几天了 求大神指教 感激不尽！！

控制台报的错是java.lang.NumberFormatException: null

Answer 1

或者，继续拆分：

 Var = ServletActionContext.getRequest().getParameter("ftId");   // 不清楚返回的数据类型，请按实现返回的数据类型定义。
 int iFtld = Integer.parseInt(Var);
 List<Teacher> teacher = TeacherApartmentService.findTeacher(iFtld);