jsp会话隐式对象在从servlet调用时抛出空指针异常。

Question

我正在使用jsp和servlet开发一个应用程序，在jsp中使用会话隐式对象面临一个问题。我正在做的是在servlet中的session对象中设置某些属性，然后将响应转发给jsp页面。现在，我想访问jsp页面中的那些会话属性，但是在这样做时，它将抛出一个空指针异常。这是我的密码：-

这是我的servlet

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html");
    PrintWriter pw=response.getWriter();
    con=Connector.myCon();
    u=request.getParameter("userName");
    p=request.getParameter("password");
    HttpSession session=request.getSession();
    session.setAttribute("userName",u); 
    session.setAttribute("userType",userType);
    RequestDispatcher rd=request.getRequestDispatcher("Home.jsp");
    rd.forward(request, response);
    }

这是我的jsp

<%
    session=request.getSession();
    String s = (String) application.getAttribute("name");
    System.out.println(s);
    String userName = (String)session.getAttribute("userName");
    if (userName == null) {
        //request.setAttribute("Error", "Session has ended.  Please logenter code herein.");
        RequestDispatcher rd = request
                .getRequestDispatcher("index.hmtl");
        rd.include(request, response);
        out.println("Session has ended.  Please login.");
    } 
    else 
    {
        String userType = (String)session.getAttribute("userType");
        System.out.println(userType);
        if(userType.equals("student")) 
        {}
    }%> 

在使用此选项时，我将得到一个空指针异常。帮帮我。

Answer 1

像这样改变，

<%
String s = (String) application.getAttribute("name");
System.out.println(s);
String userName = (String)session.getAttribute("userName");
if (userName == null) {
    //request.setAttribute("Error", "Session has ended.  Please logenter code herein.");
    RequestDispatcher rd = request
            .getRequestDispatcher("index.hmtl");
    rd.include(request, response);
    out.println("Session has ended.  Please login.");
} 
else 
{
    String userType = (String)session.getAttribute("userType");
    System.out.println(userType);
    if(userType.equals("student")) 
    {}
}%>