These are the following answers I can think of:
- If the user logs in before performing any activity, you could easily maintain session information based on the login ID.
- If there is no necessity for the user to login, you can track the clients connected at the entry point of your application and maintain a map of them. Since each user is not logging in explicitly, you might want to track the clients based on the IP address they are logging in from.
- You could assign each Swing client downloaded an unique GUID and send that along with each request.
Of course, the caveat is if there are a lot of concurrent users accessing the system, you have to implement a queuing system and also make sure that your server code is thread safe.
A completely different approach is use to JSPs or Servlets.