RMI server calling a method on a client object ?

Hi All,
I am writing a client - server application and my intention is to use RMI for comunication.
When the client has to retrive datas from the server it's easy, but let's suppose that the server has to inform the client about some updates about the data, how can I do that?
I do not want the client keeping calling methods on the server to see if there is something of new :(
Is there some way to pass an OutputStream to the client, so when the server writes someting, the client reads it ? ( the client should have a thread which keeps reading)
Or maybe I could pass a reference of a client class to the server so when the server needs to inform the client, it calls a method on this class?
thanks, Fab

The client can be a Remote Object to, passed as a remote reference when calling the server.
Basically all you'll have to do is "register" the client on the serverside.
Your serverside class would the have a:
register(RemoteClient client) method.
The server could the use this remote reference for callbacks.
So, all you have to do is declare the Remote Interface for the client and implement it, and the call the servers myRemoteServer.register(this).
If you've already implemented the server, it's a peace of cake to enhance your client.

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- It happens every single time the callback method is invoked, I see the event been deserialized client-side with the fields initialized with null values and server-side there is the java.rmi.ConnectException.
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Earlier responses pointed out something important:
when it comes to real communications, the roles of
client and server are frequently switched.Yes, but CONCEPTUALLY.
What you mean to say really, is that a process can be ASKED for some resource (then it would be acting like a "server") or it can ASK for a resource (it would be acting like a "client"). Please note that i said it ACTS like something. It is not the same thing as it REALLY BEING that thing substantially. What i'm driving at is that when you design an app, objects that make it up take dual roles at THAT LEVEL of their own operation, but universally (when you look at the ENTIRE app), things cannot switch around like that anytime they want. An RMI Server is just that: A server. Clients connect to it, and there's no reason for the server to want to connect to a client of its own volition. When you start doing that, you're messing around with WHAT IT MEANS to implement client/server arch.....For instance, the objects that make up of that talk to bound remote objects on the server, CAN act out this dual role: but not when you have a bird's eye view of the entire app.
Its bad design. Its bad practise.
>
At the "architectural" level - something I admit is
vague - I suggest that in the application described by
the original poster, the only distinctions between
client and server are
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o A client can register with a server for on-going
communications, In everything else i would agree, but not in RMI: its nature just forbids it, because it means implementing what is in the server-side......on the client-side, just so the client can be TALKED TO by the "one server", as you put it.
but not the reverse.
>
This last point is key to server-initiated
communications (using RMI). When a client registers
with a server, it passes a reference to an object that
extends Remote. The server holds onto this reference,
and when it has something to say to the clientlike what? RMI isnt built that way! the client talks to the server. End of story.
, then
the server calls a method of that remote objectimplying another server on the client-side!!! doesnt make sense at all.
>
Finally, It bears repeating in this forum: With RMI,
such "callbacks" will not work if the clients are
behind firewalls.Correct, but irrelevant: firewalls or no firewalls, WHY are you trying to do it in the first place?
It also bears repeating in this forum: RMI is client/server architecture in practice, but its the NATURE of RMI that forbids it from being used the way ANY OTHER C/S architecture out there is flexible.

RMI server calling a method on a client object ?

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