Java - How to close reset the socket which was initialized by my application and on the fly re-open it? both in TCP or UDP

Question

I have the following application which get launched as below:

Runtime.getRuntime().exec("java -cp /var/dist/Test.jar System.V PDP-11");

It has 10 to 20 second of task also it contain TCP/UDP server on port 1965 . Once that task is complete, my another hand sends an TCP byte to shutdown the System.V

Runtime.getRuntime().exec("java -cp /var/dist/Test.jar System.V PDP-11/20");

Within less then 1 seconds another action executes as above, but that fails because port 1965 is already in use. But it was killed using System.exit(0)

How do i resolve that? So that it does not say "already in use port"? It seems like it takes lot of time to de-initialize the TCP or UDP ports that was listening via Java. (where nc -l port get lot faster killed).

Follow up:

i tried following but still it takes too while to get that port available (Linux OS).

byte[] buf = new byte[50];

sock.setSoTimeout(100);

Answer 1

It takes some time for OS to "notice" that port can be used again - even if you close the socket and kill the application. Problem can be solved with following code:

ServerSocket ss = ... //initialization of socket listening on port 1965
ss.setReuseSocket(true);

Please remember that code above is only a hint for OS that is should free port as fast as possible. Some exotic implementations of TCP stack might not honour this.