client agent framework (web-services)

I have a scenario where my server side java code needs to interact with an application on the client desktop. So I was researching on if there are any simple frameworks to enable such interaction, say using web-services or pure java-servlets. I could create one custom framework to enable this, but the t开发者_如何转开发echnical challenge I foresee would be to figure out the URL (or the IP) to post the request to the client servlet. Any ideas or knowhow would be of great help.

Thanks Venkat

The obvious solution is to make the client connect to the server. After the connection is established, the server can send commands to the client directly. But of course this is not easy to do using HTTP, because you need a long-running connection.