Ensure single instance of Java application

Question

Hi,
I'd like to make sure that only one instance of my Java application can be run and I've done some search around. The recommended approach seems to be using ServerSocket that occupies a certain port.
On the other hand I've seen that JConsole could display the names of all Java processes that are running. This is perhaps another approach to the issue? JConsole is said to be a pure Java tool, so I was wondering how this is implemented. I've googled a bit but still could not find out how. Could someone please give me a hint?
Thanks a lot!

Answer 1

masijade wrote:
So what, in your mind, is wrong with the ServerSocket approach? Why do all "newbies" immediately discard this approach and then go out and try all these other complex, unreliable, obscure, and/or otherwise questionable practices?Found this thread via Google on the original Sun forums. Searching here on the exact title didn't find it!
Anyway, I'm using the ServerSocket approach:
try
   InetAddress localAddress = InetAddress.getLocalHost();
   log.info("InetAddress.getLocalHost(): " + localAddress);
   socket = new ServerSocket(12345, 1, localAddress);
   } // end try
catch (Exception e)
   throw new Exception("Program already running, exiting");
   } // end catchUnfortunately, this is not working reliably. It works some of the time; I can see in the logs the "Program already running" message. But then from time to time I'll see 4 instances running at the same time, and they are each trying to do actual work, not just hung in some exit state.
The runtime platform is Linux 2.6.9-34.ELsmp x86_64, via cron; I think it is running some version of Redhat, old obviously. Java version is 1.6.0_16, 64-bit.
The job runs every 15 minutes. Any ideas why this is not working all the time?
Thanks.
Edited by: ow003765 on Nov 3, 2010 4:01 PM