I have a client and server application that sets up RMI so the client can connect to the server for that to perform tasks when needed, however I want the server to also be able to send tasks to the client, e.g. force a popup to appear when the server sends a message to all clients as an example (I need it to do other things too).

What is the best way to achieve this, ideally I only want to set up the RMI once, is the only way to achieve this is to set up a RMI server on each client too?