Re: NullPointer error returned from ResultSet.java

Hi Barry,
You had already answered the question, sorry for not posting a follow up:).

Since the function calls itself, there will more than one resultset open. I
modified
the code to get the list into a vector before recursing. Then I used the
vector
rather than moving through the resultset. In this case there will be only
resultset open
at any time and the error doesn't come.

Thanks,
Nagarajan.


> -----Original Message-----
> From: Barry Lind [mailto:barry@xythos.com]
> Sent: Thursday, October 10, 2002 5:36 PM
> To: G.Nagarajan
> Cc: pgsql-jdbc@postgresql.org
> Subject: Re: [JDBC] NullPointer error returned from ResultSet.java
>
>
> Nagarajan,
>
> If you submit a complete test case that demonstrates the problem I would
> be willing to look into this.  But there just isn't enough information
> in what you have provided here to debug this.  I don't even know the
> exact error you are getting.
>
> thanks,
> --Barry
>
>
>
> G.Nagarajan wrote:
>  > Hi,
>  > I am also getting the same error. In my case I am using a prepared
> statement
>  > to create the resultset like
>  >
>  >   PreparedStatemet stmt = "...";
>  >
>  >   callerFunction()
>  >   {
>  >     createPreparedStatement();
>  >     fun1();
>  >     closePreparedStatement();
>  >   }
>  >   fun1()
>  >   {
>  >      Results rs = stmt.executeQuery();
>  >
>  >     while (rs.next() )
>  >     {
>  >         fun1(); //recursive call
>  >       }
>  >       rs.close();
>  >   }
>  >
>  > The null pointer exception is throws after three recursive calls. The
> code
>  > at
>  > 113 is rows.size(). Perhaps it has something to do with caching? The
> error
>  > doesn't come if I use normal statements.
>  >
>  > Regards,
>  > Nagarajan.
>  >
>  >
>  >
>  >>-----Original Message-----
>  >>From: pgsql-jdbc-owner@postgresql.org
>  >>[mailto:pgsql-jdbc-owner@postgresql.org]On Behalf Of Jeff Duffy
>  >>Sent: Monday, October 07, 2002 5:57 PM
>  >>To: pgsql-jdbc@postgresql.org
>  >>Subject: [JDBC] NullPointer error returned from ResultSet.java
>  >>
>  >>
>  >>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@alanne.com
>  >>
>  >>
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