dologin.jsp代码

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%
  String path = request.getContextPath();
  String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
  String username ="";
  String password ="";
  //request.setCharacterEncoding("utf-8");//防止中文乱码
  
  username = request.getParameter("username");
  password = request.getParameter("password");
  
  //如果用户和密码都等于admin,则登录成功
  if("admin".equals(username)&&"admin".equals(password)) {
     session.setAttribute("loginUser", username);//保存登陆的用户名
     request.getRequestDispatcher("login_success.jsp").forward(request, response);//服务器内部转发  
  }else {
     response.sendRedirect("login_failure.jsp");//请求重定向
  }
%>

login_success.jsp的如下代码显示session.getAttribute("loginUser")!=null

  <div id="box">
   <%
    String loginUser = "";
    if(session.getAttribute(loginUser)!=null){
     out.print("dsdasa");
     loginUser = session.getAttribute("loginUser").toString();
    }else{
     out.print("4515");
     out.print(session.getAttribute("loginUser"));
    }
   %>
   登陆成功！欢迎<%=loginUser%><br>
   <%=request.getParameter("username") %>
  </div>

输出显示else里面的内容，4515admin