求助！登录系统一直报错！hibernate+serv+jsp做的

jsp：
<LEGEND>用户登录</LEGEND><BR>
<DIV><LABEL for=Name>用户</LABEL> <INPUT id=name class=inpa maxLength=32 type=text
name=name> <BR></DIV>
<DIV><LABEL for=password>密码</LABEL> <INPUT id=pss class=inpa maxLength=32
type=password name=pss> <BR></DIV>
<div><label for=it>身份</label>
<select name=select>
        <option value="1">学生</option>
        <option value="2">教师</option>
        <option value="3">管理员</option>
      </select>
      <BR></div>

serv:
public class Login extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

String  name=request.getParameter("name");
String  pss=request.getParameter("pss");
String  utype=request.getParameter("select");
StudentDAO stuD=new StudentDAO();
TeacherDAO teaD=new TeacherDAO();
AdminDAO adD=new AdminDAO();
int type=0;
if(utype.equals("1"))
type=stuD.login(name,pss);
else
if(utype.equals("2"))
type=teaD.login(name,pss);
else
if(utype.equals("3"))
type=adD.login(name,pss);
response.setContentType("text/html");
     PrintWriter out = response.getWriter();
     HttpSession session=request.getSession(true);
session.setAttribute("name",name);
switch(type)
{

case 1:{
response.sendRedirect("False.jsp");
break;
}
case 2:{
response.sendRedirect("Admin.jsp");
break;
}
case 3:{
response.sendRedirect("Student.jsp");
break;
}
case 4:{
response.sendRedirect("Teacher.jsp");
break;

}

}
}

dao：
package dao;

import dao.*;
import bean.Admin;
import java.util.List;
import java.util.Set;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.LockMode;
import org.hibernate.Query;
import org.hibernate.criterion.Example;
import bean.HibernateSessionFactory;
import org.hibernate.Session;

public class AdminDAO  {

public int login(String name,String pss){
Session session=HibernateSessionFactory.getSession();
int i=0;
Admin ad=(Admin)session.get(Admin.class,name);
if(pss.equals(ad.getAds()))
i=2;
return i;
}
}

--------------------编程问答--------------------

public int login(String name,String pss){

Session session=HibernateSessionFactory.getSession();

int i=0;

Admin ad=(Admin)session.get(Admin.class,name);

if(pss.equals(ad.getAds()))

i=2;

return i;

}

空指针了。在这个方法里加个断点，看看哪个对象没有实例化 --------------------编程问答-------------------- 还有麻烦给具体代码啦》《
谢谢~ --------------------编程问答-------------------- System.out.println(HibernateSessionFactory.getSession());
这个是不是null

补充：Java ,  Web 开发