JSP空指针

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=TRSS";
public void setDatabaseDriver(String Driver){this.DatabaseDriver=Driver;}
public String getDatabaseDriver(){return(this.DatabaseDriver);}
    public  void setDatabaseConnStr(String ConnStr){this.DatabaseConnStr=ConnStr;}
public String getDatabaseConnStr(){return(this.DatabaseConnStr);}
public sqlBean(){
try{
Class.forName(DatabaseDriver);
}
catch(java.lang.ClassNotFoundException e){
System.err.println("加载驱动器有错误:"+e.getMessage());
System.out.print("执行插入有错误："+e.getMessage());
}
}
public String getString(String name)throws SQLException{
if(rs==null)throw new SQLException("ResultSet is null");
return String.valueOf(rs.getString(name));
} public ResultSet executeQuery(String sql){
ResultSet rs=null;
try{
Connection conn=DriverManager.getConnection("JDBC:microsoft:sqlserver//localhost;1433;DatabaseName=TRSS","sa","123");
Statement stmt=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
  rs=stmt.executeQuery(sql);
return rs;
}
catch(SQLException ex){
System.err.println("执行查询有错误:"+ex.getMessage());
System.out.print("执行查询有错误:"+ex.getMessage());
}
return rs;
}

public void CloseDataBase(){
try{
conn.close();
}
catch(Exception end){
System.err.println("执行关闭Connection对象有错误:"+end.getMessage());
System.out.print("执行关闭Connection对象有错误:"+end.getMessage());
}
}
}
出错信息
异 常 org.apache.jasper.JasperException: Exception in JSP: /login.jsp:96: if(request.getParameter("Sno")!=null&&request.getParameter("pwd")!=null){
7: String sql="select Sno from Ani "; 
8: ResultSet rs=db.executeQuery(sql); 
9: if(rs.next()){
10: String Sno=new String(request.getParameter("Sno").toString().getBytes("ISO-8859-1"),"GB2312"); 
11: 
12: session.setAttribute("Sno",Sno);
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:506)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:395)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
起 因 java.lang.NullPointerException
org.apache.jsp.login_jsp._jspService(login_jsp.java:61)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:334)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
注 意 完整的起因在Apache Tomcat/5.5.20里。大家帮帮小弟