Insert with replace?

What is the normal way to preform a "insert with replace" on
a row in a relational database (specifically postgresql)?

I've got a database that (logically) represents a set of
items, where each item has a primary key represented by two
columns (id and name).  If that key isn't in the database,
I want to insert the item.  If that key is in the database, I want
to update the item.  I have no need to retain the previous
values.

The interface is through jdbc.

I assume I could try the update first and then, if the update
generates an exception, perform an insert, but is there a way
to do the same with a single command?  (The data is such that
the update will fail in the majority of cases.)

Thanks! 
--
Steve Wampler-  SOLIS Project, National Solar Observatory
swampler@noao.edu