Re: Limit Single Instance


"Gordon Beaton" <not@xxxxxxxxx> wrote in message
news:43df96e5$1@xxxxxxxxxxxxxxxxxx
> On Tue, 31 Jan 2006 09:45:34 -0700, Monique Y. Mudama wrote:
>> On 2006-01-31, Allan Bruce penned:
>>> How can I limit my Java application to be running only once? I want
>>> to avoid a user being able to run the application twice, instead if
>>> they try to re-open it then it should show the main JFrame of the
>>> instance already running. Thanks Allan
>>>
>>
>> The typical way to do this (for any app, not just java) is to check
>> for a lock file on startup. If the lock file exists, don't start the
>> app. If it doesn't, create one.
>
> The other typical way is to open a ServerSocket listening on a
> specific port number. If that fails, you can assume your application
> is already running.
>
> This mechanism has two advantages:
>
> - the ServerSocket is automatically released regardless of how the
> application terminates, so no false positives are caused by failure
> to clean up (other applications or users using the same port number
> can still be a problem, so choose wisely).
>
> - a second program instance, upon failing to create the ServerSocket,
> can connect to the original and then exit, thereby signalling it to
> pop up or move to the front.
>
> /gordon
>

I had thought of something similar - my only worry is if a firewall does
anything to interfere with this?
Allan


.

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