Java Programming

i got a java client that needs to call another java server in a synchonous or a asynchronous way to get some data. i am using xml-rpc at the moment since it supports both ways. the decision to make an async or sync call depends on the amount of data cached on the client side. if the cache is empty the client uses the synchronous way, the asynchronous method call is only used if the cache reaches a minimum size.
now, it seems like on the long run this is not very efficient since xml-rpc adds quite a lot of overhead. i am also not going to use a hybrid architecture.
does anyone know if rmi supports asynchronous method invocation? or is there a better way to do it?