When using -Dcom.sun.management.jmxremote.port=0

Question

In order to bind to the next available port how can you then programmatically find out which port the agent bound do so you know which port number to use in JConsole?

Answer 1

You can't. Instead of writing code within your application to discover this port, you should write code that creates and configures a connector itself. If you have already worked out the -Dcom.sun.management.jmxremote.* properties that you need, then you can translate them into code as described here. If you create your RMI registry with LocateRegistry.createRegistry(0) then you're left with a similar problem because there's no way to extract the port number from the returned Registry object. Instead, you can use the createRegistry form that takes an RMIClientSocketFactory and an RMIServerSocketFactory, and in the latter you can extract the port number after creating a socket in the createServerSocket method, and for example store it in a local variable.
Alternatively you could create a ServerSocket(0), look at its port number, close it, then create a registry on that port number, looping a few times if it fails (because someone else grabbed that port in between).
This is admittedly not as easy as it should be.
Regards,
Éamonn McManus -- JMX Spec Lead -- [http://weblogs.java.net/blog/emcmanus]