Problem calling stored function

Hi to everyone,
I'm having this problem:
I have implemented a stored function that take as argument an integer, in
its body execute some inserts and deletes depending on the argument, and
returns 1 when ended.
I call from my java code the pgsql function in this way:

CallableStatement cs = con.prepareCall("{? = call comp(?)}");

cs.registerOutParameter(1, Types.INTEGER);

cs.setInt(2, min);

cs.execute();
Where comp is the name of the function and min is the argument passed.
When i run my java code, I obtain 1 as result, but the inserts and update
are not performed.
>From command line the stored function works, so it's not a problem of the
stored function.
Is there a problem in performing insert and update in a stored function
called by java code?
I use jdk 1.5, postgres 8.2 and JDBC4 postgresql driver 8.2-506

The connection with jdbc works, because I execute other insert not in this
stored function within java code.
Thanks for your help and excuse me and my newbye...