HTTP is a very high overhead method of doing this,
and is really only useful if you have to deal with
restrictive firewalls outside your control. SOAP also
has high overhead, but is useful when dealing
with differing object models or differing application
languages in the different tiers.

Alternatives in Java are CORBA, RMI, or simple serialization
of objects over a socket. They all have their pros and
cons - the "best" is up to you to decide, given your
architecture and legacy systems.