Different execution time from psql and JDBC

Dear postgresql community,

I have a quite complex statement. When I execute it directly via
psql, the execution time is approx. 2000 ms.

When I execute it via JDBC (Apache Cocoon), the execution time
is either 600..1000 ms or approx. 10.000 ms, based on a certain
value in a table.

An interesting point is that the value has a big impact on the
JDBC execution time, but the psql execution time is not affected
at all.

Is there a way to output the query plan (like EXPLAIN ANALYZE)
in the log files? How can I trace down the problem?

Of course I can attach the query if this helps.

Thanks a lot in advance!

-- Andreas