Servet的值为什么没有传过来？系统报空指针异常

这是Servlet方法  
public class TypeServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Typedao typedao=new Typedao();
        List<Type> allType=typedao.getAllType();
        req.getSession().setAttribute("allType",allType);
        req.getRequestDispatcher("/data/getType.jsp").forward(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);

    }
}

这是JSP

<%
    List<Type> allType= (List<Type>)session.getAttribute("allType");
    Iterator<Type> it=allType.iterator();
    while (it.hasNext()){
       Type type= it.next();
    %>
<a  href="getNotice.jsp?tno=<%=type.getTno()%>"><%=type.getTtypeName()%></a><br/>
<%
}
%>

为啥没有传过来

查看servlet 是否查询到数据