Using ResultSetMetaData.getColumnTypeName

I am trying to write some code to copy the definition of a database with all
its tables and keys, and I am trying to do it in Java using JDBC.  You may
think that I am mad and that there are better ways of doing this, but in this
case I am already within a Java app, and so using native facilities is more
trouble than it is worth.

The problem I have hit is that getColumnTypeName does not return say
numeric or int for a number, but a size specific name like int4.  If you then
use int4 as the type you can not use the precision (it is implicit I guess)
in the column type.  So you can say "fred int(10)" or "fred int4" but not
"fred int4(10)".  So I guess my question is whether there is a simple way
to work out whether a given column type name is or is not allowed to be
followed by a precision.

I suppose I could use getColumnType and convert those into strings,
but then one has to ask why getColumnTypeName exists.

David

BTW, I tried googling to find some code to do this, and I found some
MySql specific code but nothing for Postgresql.  If someone has already
done this I would much rather use tested code than reinvent the wheel.