为何跳转到servlet会有异常？？？？-----急-----

我从一个jsp页面超链接到一个servlet中，然后在servlet中设置一个session变量,然后通过response.sendRedirect()方法跳转到另外一个jsp页面.不会爆错,但是有空值异常,请问是什么问题???

解决方案 »

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<%@ page contentType="text/html; charset=GBK" %>
<%@page import="com.westaccp.*" %>
<html>
<head>
<title>
success
</title>
</head>
<body bgcolor="#ffccff">
<h1>
haha
</h1>
<%
   Users u=(Users)session.getAttribute("users");
%>
<h2>欢迎<%=u.getName()%></h2>
<a href="/myWeb/aaaa?a=2">跳转到index页面</a>
</body>
</html>
跳转到这个servlet
package com.westaccp;import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;public class Servlet1
    extends HttpServlet {
  private static final String CONTENT_TYPE = "text/html; charset=GBK";  //Initialize global variables
  public void init() throws ServletException {
  }  //Process the HTTP Get request
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws
      ServletException, IOException {
    response.setContentType(CONTENT_TYPE);
    PrintWriter out = response.getWriter();
    String a=request.getParameter("a");
    if(a.equals("1"))
    {
      String name=request.getParameter("name");
      String pwd=request.getParameter("pwd");
      Users u=new Users();
      u.setName(name);
      u.setPwd(pwd);
      HttpSession s=request.getSession();
      s.setAttribute("users",u);
      response.sendRedirect("success.jsp");
    }
    if(a.equals("2"))
    {
       Users u=new Users();
       u.setName("hello");
       u.setPwd("fine");
       HttpSession s=request.getSession();
       s.setAttribute("users1",u);
       response.sendRedirect("index.jsp");
    }  }  //Process the HTTP Post request
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws
      ServletException, IOException {
    doGet(request, response);
  }  //Clean up resources
  public void destroy() {
  }
}跳转到下一个jsp<%@ page contentType="text/html; charset=GBK" %>
<%@page import="com.westaccp.*" %>
<html>
<head>
<title>
index
</title>
</head>
<body bgcolor="#ccffff">
<h1>
haha
</h1>
<%
   Users u=(Users)session.getAttribute("users1");
%>
<h2>»¶ӭ<%=u.getName()%></h2>
</body>
</html>
//servlet
……
s.setAttribute("users",u);
……//jsp
<%
Users u=(Users)session.getAttribute("users1");
%>
=====================
细心啊
...
if(a.equals("1"))
    {
      String name=request.getParameter("name");
      String pwd=request.getParameter("pwd");
...
我从你的页面上看,request.getParameter("name");你能获到值吗?你能获到那才叫真是奇怪乐!
<a href="/myWeb/aaaa?a=2">跳转到index页面</a>就这个你是不能获到name和pwd的,
response.sendRedirect() 方法不能傳遞session中的對象的。