How to make sure that only a single instance of a Java application is running?

Question

I want my application to check if another version of itself is already running.

For example, demo.jar started, user clicks to run it again, but the sec

Answer 1

If your application is running on Windows, you can call CreateMutex through JNI.

jboolean ret = FALSE;    
HANDLE hMutex = CreateMutex(NULL, FALSE, mutexName); 
ret = TRUE;    
if(WAIT_TIMEOUT == WaitForSingleObject(hMutex, 10))  
{    
    ret = FALSE;  
}
else if(GetLastError() != 0)  
{    
    ret = FALSE;  
}

This returns true if nobody else is using this mutex, false otherwise. You could provide "myApplication" as a mutex name or "Global\MyApplication" if you want your mutex to be shared by all Windows sessions.

Edit: It's not as complicated as it looks :) and I find it clean.