问题 java.lang.NullPointerException ，麻烦找下问题。

我从网上下了个BBS ，想借用下登录代码，自己建数据库，改字段名称却不能使用，用他的表就行。
把代码贴上来，帮我看看。在网上查询了很久，说是
主要有以下几种原因： 
1、使用了未初始化的变量（虽然已经声明） 
2、使用了未初始化的对象（虽然已经声明） 
3，使用了关键字或已存在的类名作变量对象方法或类名。 可我找不到问题在哪里！______________________________________________________________________
<%@ page contentType="text/html;charset=gb2312"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>用户登录</title>
</head>
<script language="javascript">
<!--
function check(form)
{
    if (form.bbsuser.value=="")
     {
     alert("请填写用户名！");
     form.bbsuser.focus();
     return false;
   }
    if (form.password.value=="")
     {
     alert("请填写密码！");
     form.password.focus();
     return false;
   }
    if (form.useryz.value=="")
     {
     alert("请输入验证码！");
     form.useryz.focus();
     return false;
   }
return true;
}
//-->
</script>
<body leftmargin="8" topmargin="0">
<FORM METHOD=POST ACTION="userloginact.jsp" onSubmit="return check(this)">
  <br>
  <br>
  <br>
  <br>
  <br>
  <br>
  <table width="35%" border="0" align="center" bgcolor="#333333" cellspacing="1" cellpadding="0">
    <tr bgcolor="#9999cc"> 
      <td colspan="2" height="25"> 
        <div align="center"><font color="#FFFFFF">用户登录，请先输入用户名和密码</font></div>
      </td>
    </tr>    <tr bgcolor="#F8F8F8" height=25> 
  <TD> 
        <div align="right">用户名：</div>
      </TD>
<TD>
&nbsp;
        <INPUT TYPE="text" NAME="bbsuser" class="input" size="15">
      </TD>
</TR>
    <tr bgcolor="#F8F8F8" height=25> 
  <TD> 
        <div align="right">密　码：</div>
      </TD>
<TD>
&nbsp;
        <INPUT TYPE="password" NAME="password" class="input" size="15">
      </TD>
</TR>
    <tr bgcolor="#F8F8F8" height=25> 
  <TD height="22"> 
        <div align="right">验证码：</div>
      </TD>
<TD>
&nbsp;
        <INPUT NAME="useryz" TYPE="text" class="input" id="useryz" size="4">
        <img src="image.jsp" border=0 align="absmiddle"> </TD>
</TR>
    <tr bgcolor="#F8F8F8" align=center> 
  <TD colspan=2 height="30">
        <input type="hidden" name="act" value="y">
        <INPUT TYPE="submit" value="登录" name="" class="button">
        <A HREF="register.jsp"><FONT COLOR="blue">[注册新用户]</FONT></A> </TD>
</TR>
</TABLE>
</FORM>
</body>
</html>_________________________________________________________________
<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*"%>
<%@ page import="java.sql.*"%> 
<%@ page import="java.util.*"%>
<%@ page import="java.util.Date"%>
<%@ page import="java.text.*"%>
<%@ include file="inc/conn.jsp"%>
<%
  String username = new String(request.getParameter("bbsuser").getBytes("iso-8859-1"));
  String pass = new String(request.getParameter("password").getBytes("iso-8859-1"));
  String rand = (String)session.getAttribute("rand");
  String useryz = request.getParameter("useryz");
  if (rand.equals(useryz))
     {
    String sql="select * from staff where uname='"+username+"' and password='"+pass+"'";
    ResultSet rs=stmt.executeQuery(sql);
     //rs.next();
 if (rs.next())
    {
String bbsuser=rs.getString("nickname");
String name=rs.getString("uname");
String bz=rs.getString("bbsmanager");
String bbsadmin=rs.getString("bbsadmin");
String payuser=rs.getString("payuser");
    if (rs.getString("payuser").equals("3"))
       {
           out.print("<script language='javascript'>");
           out.print("alert('对不起,你的用户名被管理员封锁了!');");
           out.print("history.go(-1);");
           out.print("</script>");
           out.close();
   }
else
  {
     //Cookie c=new Cookie("clubusername",username);
     //response.addCookie(c);
 //Cookie d=new Cookie("pass",pass);
     //response.addCookie(d);
 session.setAttribute("bbsuser",bbsuser);
 session.setAttribute("name",name);
 session.setAttribute("bz",bz);
 session.setAttribute("bbsadmin",bbsadmin);
 session.setAttribute("payuser",payuser);
 
 String sqlstr="update staff set lasttime=getdate(),tili=tili+100 where clubuser_name='"+(String)session.getAttribute("name")+"'";
     stmt.executeUpdate(sqlstr);
 
     out.print("<script language='javascript'>");
     out.print("window.location.href='main.jsp';");
     out.print("parent.left.document.location.reload();");
 //out.print("history.go(-1);");
     out.print("</script>");
     out.close();
      }
    }
 else
   {
        out.print("<script>");
         out.print("alert('用户名或密码错误');");
         out.print("window.location.href='userlogin.jsp';");
         out.print("</script>");    
}
 stmt.close(); 
     conn.close();
}
  else
{
        out.print("<script>");
         out.print("alert('验证码输入有误!请核对!');");
         out.print("window.location.href='userlogin.jsp';");
         out.print("</script>");
}
%>____________________________________________________________
错误提示：
____________________________________________________________
HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:122)
root cause java.lang.NullPointerException
org.apache.jsp.crm.userloginact_jsp._jspService(userloginact_jsp.java:93)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:122)
note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.

解决方案 »

  1.   

    String username = new String(request.getParameter("bbsuser").getBytes("iso-8859-1"));
      String pass = new String(request.getParameter("password").getBytes("iso-8859-1"));
      String rand = (String)session.getAttribute("rand");
      String useryz = request.getParameter("useryz");
    是不是要改成request.getAttribute("bbsuser").
      

  2.   

    rs.getString("payuser").equals("3");改成"3".equals(rs.getString("payuser"));
    试试
    那不都告诉你了吗org.apache.jsp.crm.userloginact_jsp._jspService(userloginact_jsp.java:93)
    93行，去找到userloginact_jsp.java.应该在服务器的classes下。
      

  3.   

    会不会是String rand = (String)session.getAttribute("rand");这个值第一次时候为空