以下2段代码出现java.lang.NullPointerException怎么办

以下2段代码出现java.lang.NullPointerException怎么办change.jsp 
<%@ page contentType="text/html; charset=GB2312" language="java" import="java.sql.*,java.util.*" errorPage=""%> 
<html> 
<head> 
<title>修改记录</title> 
<meta http-equiv="Content-Type" content="text/html; charset=gb2312"> 
</head> 
<body bgcolor="#FFFFFF" text="#000000"> 
<div align="center"><font color="#000000" size="5">修改记录</font> </div> 
<%! String dingdan,url,sql,Sex,user,password; %> 
<%! Connection conn; %> 
<%! ResultSet rs; %> 
<%! Statement stmt; %> 
<% 
dingdan=request.getParameter("dingdan").trim(); 
try{ 
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newInstance(); 
url="jdbc:odbc:yuebiao"; 
user="admin"; 
password="123456"; 
conn=DriverManager.getConnection(url,user,password);//建立与数据库的连接 
stmt=conn.createStatement(); 
sql="select * from tongji where dingdan='"+dingdan+"'"; 
rs=stmt.executeQuery(sql); 
while(rs.next()){ 
%> 
<form name="form1" method="post" action="change_query.jsp?dingdan=<%=dingdan%>"> 
<table width="35%" border="1" cellspacing="1" cellpadding="1" align="center"> 
<tr> 
<td width="46%" align="center">订单号 </td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<%=rs.getObject(1)%></td> 
</tr> 
<tr> 
<td width="46%" align="center">项目 </td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<input type="text" name="project" size="8" value=<%=rs.getObject(2)%>></td> 
</tr> 
<tr> 
<td width="46%" align="center">本月品别 </td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<input type="text" name="pinbie" size="8" value=<%=rs.getObject(3)%>></td> 
</tr> 
<tr> 
<td width="46%" align="center">本月干量</td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<input type="text" name="ganliang" size="2" value=<%=rs.getObject(4)%>></td> 
</tr> 
<tr> 
<td width="46%" align="center">本月品质%</td> 
<td width="54%">&nbsp;&nbsp;&nbsp;<input type="text" name="pinzhi" size="8" value=<%=rs.getObject(5)%>></td> 
</tr> 
<tr> 
<td width="46%" align="center">本月铜量</td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<input type="text" name="tongliang" size="8" value=<%=rs.getObject(6)%>></td> 
</tr> 
<tr> 
<td width="46%" align="center">本月止干量</td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<input type="text" name="ganliang1" size="8" value=<%=rs.getObject(7)%>></td> 
</tr> 
<tr> 
<td width="46%" align="center">本月止品位%</td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<input type="text" name="pinwei" size="8" value=<%=rs.getObject(8)%>></td> 
</tr> 
<tr> 
<td width="46%" align="center">本月止含铜</td> 
<td width="54%"> &nbsp;&nbsp;&nbsp;<input type="text" name="hantong" size="8" value=<%=rs.getObject(9)%>></td> 
</tr> 
<tr align="center"> 
<td colspan="2" align="center"> 
<input type="submit" name="Submit" value="提交">&nbsp;&nbsp;&nbsp; 
<input type="reset" name="reset" value="清空"> 
</td> 
</tr> 
</table> 
</form> 
<% 
} 
rs.close(); 
stmt.close(); 
conn.close(); 
} 
catch(Exception e){ 
out.println(e); 
} 
%> 
</body> 
</html> 
change_query.jsp <%@ page contentType="text/html; charset=GB2312" language="java" import="java.sql.*,java.util.*" errorPage=""%> 
<html> 
<head> <title>修改记录</title> 
</head> 
<body> 
<%! String dingdan,project,factory,pinbie,url,sql,user,password,a,b,c,d,e,f; %> 
<%! float ganliang,pinzhi,tongliang,ganliang1,pinwei,hantong;%> 
<%! Connection conn;//定义数据库连接对象 %> 
<%! Statement stmt;//定义SQL语句对象 %> 
<% 
dingdan=request.getParameter("dingdan").trim(); 
dingdan=new String(dingdan.getBytes("ISO-8859-1")); 
project=request.getParameter("project").trim(); 
project=new String(project.getBytes("ISO-8859-1")); 
factory=request.getParameter("factory").trim(); 
factory=new String(factory.getBytes("ISO-8859-1")); 
pinbie=request.getParameter("pinbie").trim(); 
pinbie=new String(pinbie.getBytes("ISO-8859-1")); 
a=request.getParameter("ganliang").trim(); 
ganliang= Float.parseFloat(a); b=request.getParameter("pinzhi").trim(); 
pinzhi= Float.parseFloat(b); 
c=request.getParameter("tongliang").trim(); 
pinzhi= Float.parseFloat(c); 
d=request.getParameter("ganliang1").trim(); 
ganliang1= Float.parseFloat(d); 
e=request.getParameter("pinwei").trim(); 
pinwei= Float.parseFloat(e); 
f=request.getParameter("hantong").trim(); 
hantong= Float.parseFloat(f); 
try{ 
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newInstance(); 
url="jdbc:odbc:yuebiao"; 
user="admin"; 
password="123456"; 
conn=DriverManager.getConnection(url,user,password);//建立与数据库的连接 
stmt=conn.createStatement(); 
sql="update tongji set project='"+project+"',factory='"+factory+"',pinbie='"+pinbie+"',ganliang='"+a+"',pinzhi='"+b+"',tongliang='"+c+"',ganliang1='"+d+"',pinwei='"+e+"',hantong='"+f+"' where dingdan='"+dingdan+"'"; 
stmt.executeUpdate(sql); stmt.close(); 
conn.close(); 
out.println("<font size=3 color=blue>正在修改记录，请稍后......</font><meta http-equiv='refresh' content='2;url=list.jsp'>"); } 
catch(Exception e){ 
out.println(e); 
} 
%> 
</body> 
</html> 以上2段代码怎么改才好？