How to control already updated files with JAVA API?

Than

ks for the response and I'm sorry if I wasn't clear.

But anyways, I need the API to tell me what files have been already uploaded to dropbox.
When you have a Dropbox folder in your PC.
Like this:

Just to illustrate, the goal of my app is to create a folder for each client, allowing the client to add files to the folder, so that the app can upload those files through the Dropbox API. However, it can't be a shared folder, because if the client delete a file, this file can not be deleted in the server. Or, if the client already sent a file, the app should not upload this file again or replace a existing file.

Thank you!