jsp连接问题

我用login.jsp登陆到主界面时候出现了下面的错误提示：
type Exception report
message 
description The server encountered an internal error () that prevented it from fulfilling this request.
exception org.apache.jasper.JasperException: java.lang.NullPointerException        org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:522)        org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)        org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)        org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)        javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause java.lang.NullPointerException        org.apache.jsp.gzgl.reg_jsp._jspService(reg_jsp.java:82)        org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)        javax.servlet.http.HttpServlet.service(HttpServlet.java:803)        org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)        org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:337)        org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)        javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.16 logs.
我的reg.jsp的代码如下：
<%@ page import="java.sql.*"%>
<%@ page import="java.util.*" %>
<%@ page session="true" %>
<jsp:useBean id="db" scope="page" class="gzgl.util.DataBase" />
<%request.setCharacterEncoding("GBK");%>
<html>
<body>
<%
    String check,password,user,name,acl,dep;
    user=request.getParameter("user");
    password=request.getParameter("password");
    String sql="select * from hr_yh where yh='"+user+"' or name='"+user+"'";
    ResultSet rs=db.execQuery(sql);
    if(rs.next())
    {
        check=rs.getString("password");
        check=check.trim();
        user=rs.getString("yh");
        user=user.trim();
        name=rs.getString("name");
        name=name.trim();
        acl=rs.getString("acl");
        acl=acl.trim();
        dep=rs.getString("dep");
        dep=dep.trim();
  
        if(check==null||!password.equals(check))
        {
            rs.close();
            db.closeConn();
            db.closeStmt();
            response.sendRedirect("index.jsp");
        }else{
            session.putValue("user",user); 
            session.putValue("name",name); 
            session.putValue("acl",acl);
            session.putValue("dep",dep);
            rs.close();
       
            db.closeStmt();
            db.closeConn();
            response.sendRedirect("gzgl_main.jsp"); 
        }
    }else{ 
        check="";
        user="";
        name="";
        acl="";
        dep="";
        rs.close();
   
        db.closeStmt(); 
        db.closeConn();
        response.sendRedirect("index.jsp");
    }%> 
</body>
</html>
请各位大侠帮忙看看哪里出错啦。我是初学者没有头绪，很苦恼啊！ 谢谢啦！