帮小弟我看看这个有关问题如何解决

帮我看看这个问题怎么解决
org.apache.jasper.JasperException: An exception occurred processing JSP page /display.jsp at line 3

1: <%@ page language="java" import="java.sql.*" contentType="text/html;charset=GB2312"%>
2: <%String username=(String) session.getAttribute("username");
3: if(username.equals("")) response.sendRedirect("index.jsp");
4: %>
5: <%
6: String path = request.getContextPath();


java.lang.NullPointerException

[解决办法]
NullPointerException

最好解决了, 首先确定到底是哪个变量是null...
[解决办法]
if(username==null||username.equals("")) response.sendRedirect("index.jsp"); 

[解决办法]
if (username==null || username.equals(""))
{
response.sendRedirect("index.jsp");
}

先判断是不是null 再判断值是不是空
[解决办法]

HTML code

<%@ page language="java" import="java.sql.*" contentType="text/html;charset=GB2312"% > <%String username=(String) session.getAttribute("username"); if(username==null || username.equals("")) response.sendRedirect("index.jsp"); % > <% String path = request.getContextPath();
[解决办法]
session 的问题!
我的异常网推荐解决方案：An exception occurred processing JSP page,http://www.myexception.cn/j2se/33144.html