JSP空指针 - Java / Web 开发

关键代码：

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" %>
<%@page import="stu.*"%>

<jsp:useBean id="db" scope="page" class="javabean.sqlBean"/>
<%
if(request.getParameter("Sno")!=null&&request.getParameter("pwd")!=null){
String sql="select Sno from Ani where Sno='"+request.getParameter("Sno")+"'and pwd='"+request.getParameter("pwd")+"'"; 
ResultSet rs=db.executeQuery(sql); 
if(rs.next()){
String Sno=new String(request.getParameter("Sno").toString().getBytes("ISO-8859-1"),"GB2312"); 

session.setAttribute("Sno",Sno);

response.sendRedirect("denglu.jsp");
}else
 response.sendRedirect("error.jsp");
}
%>

javaBean代码：
package javabean;
import java.sql.*;
import java.io.*;
public class sqlBean {
public Connection conn=null;
public ResultSet rs=null;
  public String user="sa";
  public String password="123";
private String DatabaseDriver="com.mrcrosoft.JDBC.aqlserver.SQLServerDriver";
private String DatabaseConnStr="JDBC:microsoft:sqlserver//localhost;1433;DatabaseName=TR