RMI question

[Frans Verbeke]

Can I setup an RMI registry on a random port (by giving 0 as port parameter) and then find out wich port was chosen ?

If so, how ?

[Edward Harned]

No. Choose a port such as:
The port numbers are divided into three ranges: the Well Known Ports,
the Registered Ports, and the Dynamic and/or Private Ports.

The Well Known Ports are those from 0 through 1023.
The Registered Ports are those from 1024 through 49151
The Dynamic and/or Private Ports are those from 49152 through 65535

[Frans Verbeke]

Thanks for your reply.

The problem is I can't say in advance if a port will be free or not.

So... a solution for me would be to choose a range of ports. For example: 2000 - 2100.
And then start by trying one...if it doesn't work, try another one...and so on, till I find one that works.

Will I get a recoverable(by trying another port) exception when a port isn't free ?

[Edward Harned]

1099 is a port registered to be the RMI Registry port.

What you're doing is outside anything I know about. Perhaps other will step in here.

[Frans Verbeke]

Yes, it seems 1099 is the standard port for this. Nevertheless I was hoping to be able to choose another port.

In the API docs I found this:

public static Registry createRegistry(int port) throws RemoteException

Creates and exports a Registry instance on the local host that accepts requests on the specified port.

The Registry instance is exported as if the static UnicastRemoteObject.exportObject method is invoked, 
passing the Registry instance and the specified port as arguments, except that the Registry instance is exported with a well-known object identifier, 
an ObjID instance constructed with the value ObjID.REGISTRY_ID.

Parameters:
    port - the port on which the registry accepts requests 
Returns:
    the registry 
Throws:
    RemoteException - if the registry could not be exported
Since:
    JDK1.1

Which makes me think it's possible to choose another port.

Except the RemoteException I don't see any other exceptions listed, so I was wondering if it would be possible to try ports till I find one that's free.

I could be totally wrong here; it's not like I have experience with RMI.

Any input is always appreciated.

[Jimmy Clark]

When you manually start the RMI server (registry) you select the port that you want it to use.

Before you manually start the RMI server (registry) you should know what port you will use.

Your concept of "trying" ports until one is free does not apply to the activity of manually starting the RMI server (registry.)

[Frans Verbeke]

Jimmy Clark wrote:
When you manually start the RMI server (registry) you select the port that you want it to use.
Your concept of "trying" ports until one is free does not apply to the activity of manually starting the RMI server (registry.)

Ok, I guess I'll just have to try it. If necessary I can allways check if a port is free by doing something like the following.

bool portTaken = false;
ServerSocket socket = null;
try {
    serverSocket = new ServerSocket(portNumber);
} catch (IOException e) {
    portTaken = true;
} finally { 
    // Clean up
    if (socket != null) socket.close(); 
}

The only problem with this could be something takes the port between me checking if it's free and actually using it with the registry, but the chance on that is small enough.

Maybe you're wondering how I will be able to use this registry if I don't know beforehand what port I'll use...I will probably be sending out udp packets to tell clients what port to use.

Thank you for thinking with me here and sorry for using your time.