Object Has Been Closed

i am running a java program in tomcat to connect SQL Server,using the Microsoft's jdbc driver ,as the following code :

import java.sql.*;
class Bkjz{
ResultSet rs=null;
String spde;
String condition;
Connection con=null;
Statement sql;
public String getSpde(){
return spde;
}
public void setSpde(String spde){
this.spde=spde;
}
public ResultSet Searchsjk(){
try {
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
con=DriverManager.getConnection("jdbc:microsoft:sqlserver://localhost:1433;databasename=zkbm","zkbm","zkbm");
sql=con.createStatement(ResultSet.TYPE_SCROLL_SENS ITIVE,ResultSet.CONCUR_READ_ONLY);
if(spde.equals(""))
condition="select CRCC,CRNM,SPDE,SPNM from SPCR where EMTP='5'group by SPDE,SPNM,CRCC,CRNM";
else
condition="select CRCC,CRNM,SPDE,SPNM from SPCR where SPDE='"+spde+"'"+"and EMTP='5' group by SPDE,SPNM,CRCC,CRNM";
rs=sql.executeQuery(condition);
//con.close();
if(!rs.next())
{
return null;
}
else
{
rs.previous();
return rs;
}



}
catch(Exception e){
message="exception!!! "+e.toString();
System.out.println(e);
return null;
}



}
}
public class Bk{
public static void main(String args[]){
Bkjz bbb=new Bkjz();
bbb.setSpde("1020110");
try{
ResultSet rr=bbb.Searchsjk();

while(rr.next()){
System.out.println(rr.getString("CRCC"));
}
}
catch(Exception e){
System.out.println(e);
}
}
}


without con.close(),it can return Resultset ,but when includeing con.close(),an Exception tell me:Object has been closed, in other programms i've close connection,but it never throws this Exception,why? thanks