Multiple instances of jvm

Question

Hi
How would I go about ensuring that an application could only instantiate itself once? If it�s put into an executable Jar for example it presently instantiates itself as many times as you click on it. I don't want to prevent other java apps from working, but just stop duplicates of themselves. The only solution I�ve found is to keep a record of the applications started on a txt file and to get any new app to read this at the start-up and exit if one is already running. This is not elegant and there must a better solution.
Thanks in advance

Answer 1

There probably aren't any really elegant solutions but the following provides a java only solution.
First instance:
It starts and trys to use a socket to connect to a specific port (put this in a config file if you like) to localhost (same box.) It will fail, so it then creates a socker server to the same port.
Second instance:
It starts and trys to use a socket to connect to a specific port. It will succeed, so exit the application.
You can embellish this in various ways if you are concerned that something else might be using the socket.