org.apache.jasper.JasperException和java.lang.NullPointerException错误。

[iknight]

代码如下：
<%@page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" import="java.text.*"%>

<jsp:useBean id="user" class="conn.userinfo" scope="session"/>
<%
String whereTo,tempstr,tempint;
byte[] tmpbyte;
String username=request.getParameter("username");
String userpassword=request.getParameter("userpassword");
username=username.trim();
userpassword=userpassword.trim();
tmpbyte=username.getBytes("ISO8859_1");
username=new String(tmpbyte);

if ((username==null)||(userpassword=="")) {
errmsg="请输入用户名及密码";
%>
<%whereTo="login.jsp&errmsg="+errmsg;%>
<jsp:forward page='<%=whereTo%>'/>
<%
} //'end if

if (!user.checkUserPassword(username,userpassword)) {
errmsg="密码错误！";
%>
<%whereTo="login.jsp&errmsg="+errmsg;%>
<jsp:forward page='<%=whereTo%>'/>
<%}
else {
username =user.getUserName();
String userphone =user.getUserPhone();
String useroicq =user.getUserOicq();
String useremail =user.getUserEmail();
String userhomephone =user.getUserHomePhone();
String userworkphone =user.getUserWorkPhone();
String userbp =user.getUserBp();
String userworkaddress=user.getUserWorkAddress();
String userhomeaddress=user.getUserHomeAddress();
String userremark =user.getUserRemark();
String userid =user.getUserId();
%>

<form name="form1" method="post" action="modify.jsp">
<table width="498" border="0" align="center">
<tr>
<td><font color=red>ID : <%=userid%></font></td>
</tr>
<tr>
<td valign="top"><div align="center">姓名：</div></td>
<td><input name="name" type="text" id="name" value="<%=username%>"></td>
</tr>
<tr>
<td valign="top"><div align="center">手机：</div></td>
<td><input name="phone" type="text" id="phone" size="40" value="<%=userphone%>"></td>
</tr>
<tr>
<td valign="top"><div align="center">QQ：</div></td>
<td><input name="oicq" type="text" id="oicq" size="40" value="<%=useroicq%>"></td>
</tr>
<tr>
<td valign="top"><div align="center">E-mail:</div></td>
<td> <input name="email" type="text" id="email" size="40" value="<%=useremail%>"> </td>
</tr>
<tr>
<td valign="top"><div align="center">家里电话:</div></td>
<td> <input name="homephone" type="text" id="homephone" size="40" value="<%=userhomephone%>"> </td>
</tr>
<tr>
<td valign="top"><div align="center">单位电话:</div></td>
<td> <input name="workphone" type="text" id="workphone" size="40" value="<%=userworkphone%>"> </td>
</tr>
<tr>
<td valign="top"><div align="center">BP机:</div></td>
<td> <input name="bp" type="text" id="bp" size="40" value="<%=userbp%>"> </td>
</tr>
<tr>
<td valign="top"><div align="center">工作单位:</div></td>
<td> <input name="workaddress" type="text" id="workaddress" size="40" value="<%=userworkaddress%>"> </td>
</tr>
<tr>
<td valign="top"><div align="center">家庭地址:</div></td>
<td> <input name="homeaddress" type="text" id="homeaddress" size="40" value="<%=userhomeaddress%>"> </td>
</tr>
<tr>
<td valign="middle"> <div align="center">备注:</div></td>
<td><textarea name="remark" cols="55" rows="" id="remark" value="<%=userremark%>"></textarea></td>
<td> </td>
</tr>

</table>
<p align="center">
<input type="submit" name="Submit" value="更改">
  <a href="txl.jsp">返回</a>
<!--<input type="button" name="Submit2" value="关闭" onClick="window.close()">-->
</p>
</form>
<!---------------------------------------------------------------->
<%}%>
我从另外一页提交username和userpassword后，到本页就出现org.apache.jasper.JasperException和java.lang.NullPointerException错误。
请问这是怎么回事？谢谢！！！

[zhxx]

你要使用的对象为NULL
仔细检查一下