u can write a trigger for before insert  statement on your table  that pybass this
error.
or try catch and ignore your exception. or write an stored procedure to do the
same
operation or use sequences or check before insert or .... or.... or ... its up
to u.

You don't want any message if a violation occurs???
If you're not, I think that the best way to do this is a stored procedure
directly from the database. Case your RDBMS does not supports procedures, I
suggest you to create a function "insert" and before the insert  use a "select
count(*) from table1 where col2 = id" statement  to check if the record exists.

you can also do this without error by enclosing the
statement.executeUpdate or whatever u r using directly
in the try and catch... e.g.

try // main block for connection establishment etc.
{
.....connection
.. prepared Statement


loop {
try {
execute statement;
} catch (SQLException e){}
}



} catch ()
{
}

could just run the values through a SELECT first and see if you get any
hits...

resultSet = stmt.executeQuery("select primaryKey where primaryKey=VALUE");

if (!resultSet.next()){
..do update
}