Re: NullPointer error returned from ResultSet.java

Jeff,

You can't have two result sets open on the same connection.

Dave
On Mon, 2002-10-07 at 11:57, Jeff Duffy wrote:
> Greetings,
>
> I have a JSP page with a rather large scriptlet that uses multiple nested
> statements and ResultSets. Under very specific conditions I am encountering
> the following error:
>
> java.lang.NullPointerException
> at org.postgresql.jdbc2.ResultSet.next(ResultSet.java:113)
>
>
> Here's one pertinent snippet of my code:
> ( This code begins inside a while(rs.next()) loop for ResultSet rs,
> using Statement stmt)
>
>
> sql.append("AN SQL QUERY");
> rs2 = stmt2.executeQuery(sql.toString());
>
> while(rs2.next()){
> String courseId = rs2.getString(1);
> String roleName = rs2.getString(2);
>
> rs3 = stmt3.executeQuery("SELECT nextval('assignment_id')");
> rs3.next();
> assignmentId = rs3.getString(1);
>
> sql.delete(0, sql.length());
> sql.append("AN SQL QUERY");
> stmt3.executeUpdate(sql.toString());
> }
>
> Through debugging it appears that rs2 is throwing the error; the message
> states the error is in method next(), but if I have only zero records or
> only one record in rs2, there is no error. It's only when I have multiple
> records that the error is thrown the second time round the while loop, so I
> suspect it may be thrown at the assignment of courseId.
>
> This error is reproduced given the same conditions (nested ResultSets with
> the innermost ResultSet executing an Update inside a while(ResultSet.next())
> loop. It almost seems that the call to rs3.executeUpdate() is closing rs2,
> but I cannot see why that would happen. This is occurring in at least six
> different source files.
>
> If I create a new Vector and stuff the contents of rs2 into it, then
> iterate over the vector and use rs3 as shown above, no error is thrown.
>
> Updating to the 7.3beta1 JDBC driver changes the error message to:
>
> javax.servlet.ServletException: postgresql.con.closed
>
> which is even more puzzling.
>
>
> Notes about my coding style that may be relevant:
> - I use one StringBuffer for all sql queries and clear it for each new query
> for efficiency. This hasn't ever caused problems elsewhere.
>
> - I predeclare all Statement and ResultSet objects at the outermost block of
> code (the 'top') like so:
>
> Statement stmt = conn.createStatement();
> Statement stmt2 = conn.createStatement();
> Statement stmt3 = conn.createStatement();
> ResultSet rs, rs2, rs3;
>
> Other data:
>
> - The connections are obtained from a custom class that uses the jdbcpool
> pool manager.
> - I'm using the Sun JDK v1.4.0 for Linux (it happens on Win32 as well).
> - The JDBC library is v7.2 (the pgjdbc2.jar binary download).
> - PostgreSQL 7.2.1 on i686-pc-linux-gnu, compiled by GCC 2.96
>
> Any flashes of insight?
>
> Thanks
>
> Jeff Duffy
> jeff(at)alanne(dot)com
>
>
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