user import and update

Hello experts,

I would appreciate an advice, just to know if it should be possible to use existent moodle webservice (in case, which webservice) to (make a tool in java to) import a CSV file containing new users to import and update existent users; if not a mass file, but at least a single user, as soon as someone saves a new  user or modifies an existing user in an external java program.

At the moment I import a file with 3000 users every day (most of which already exist) with the moodle administration GUI.

Any answer would be appreciated. Thanks,

Michael