I'm not sure but it seems more like a synchronization problem with the
Database Pool Servlet. Maybe the database connection isnt being released
back to the pool correctly. You may want to write your own Database
connection object and skip the pool. Test your servlet with that and see if
the problem goes. If it does then I guess you've isolated the problem to the
Database pooling.............
Amit Karandikar
4C Solutions, Inc.
Programmer / Analyst
Off Phone: (309) 751 6196
-----Original Message-----
From: Mark Wurm [mailto:[EMAIL PROTECTED]]
Sent: Thursday, March 11, 1999 3:12 PM
To: [EMAIL PROTECTED]
Subject: Servlets with Informix and LiveConnect
I have a LiveConnect application (Enterprise Server 3.5.1
with JRUN 2.2
running on HP-UX 10.20) which I would prefer not to rewrite
in its
entirety.
I need to implement some data manipulation processes that
are so easy
to do in java. but which LiveConnect will not support.
I reach a point in my application where I want to do a data
base lookup
(Informix 9.14.UC3), so I invoke a redirect to a servlet.
That servlet
calls a second servlet (database connection pool --
shamelessly similar
to the one in Mr. Moss' terrific book) and retrieves a
connection. The
first
servlet uses the connection to perform the lookup,
manipulates the data,
and creates an HTML page. This all works great. I was
amazed at how
easy it was --- until . . .
If I invoke two lookups at the same time, Informix gives me
an error on
one
of
my connections that says there was a null pointer exception
on a blob
type
column, and that the error should never occur. If the error
recurs, the
message
says, contact Informix support. It does, and I did, but
they don't have
an
answer yet, so I'm posting this letter hoping someone has
encountered
something similar.
The process works fine with sequential requests, only
simultaneous
requests fail.
I separated my servlet invocation from the LiveConnect
application. In
the
original code, I sent the servlet a fairly complex SQL query
as a
string,
so I just hard coded a query into the servlet and invoked it
from the
URL
line of my browser. Same problem.
Since only one column in the table was a blob, I thought
that might be
masking
some other issue. I stopped fetching that column. The
error changed to
a
267:
"The FREE statement released the resources that are
attached to the
cursor named in this statement. Before you can use the
cursor, you must
again prepare the SQL statement that is associated with it.
If the
cursor
was declared FOR a statement, re-execute its DECLARE
statement. If it
was declared FOR a statement identifier, execute the PREPARE
statement
again.
Well, gee, I wasn't even using a PreparedStatement; I was
using a simple
Statement.executeQuery(myQuery). So I recoded the servlet
to use a
PreparedStatement and, voila, the error went away. (I'm
using the
intersolv
class 4 jdbc driver level 1.22) Then I reimplemented my
fetch of the
blob
column. Continued success!
Feeling really smart, I reassembled everything to use
LiveConnect again.
The error returned.
I think it sounds like a jdbc driver problem. Informix is
checking into
that.
When LiveConnect does a redirect, I think LiveConnect should
be out
of the picture, so I am baffled at what influence it can
have on the
process.
I was under the impression that the redirect was a request
for the doGet
method of the servlet which is under JRUN's control. JRUN
then
interfaces
between the java process and the httpd process, but only
insofar as
the httpd process serves to send the output to the correct
client.
True?
False? Maybe? Help!
Mark
--
Mark R. Wurm
312-424-3766
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