Hi Moris,
There are 2 ways to achieve this:
1. You can submit from client via guideBridge submit API. This would take care of removing draft and adding a submission itself.
2. To do this from your servlet, there is no clear-cut existing solution but is achievable, but first you'd need to know which submit action you'd want to use as per your requirements. To delete a draft, you'd need to invoke Forms Portal Draft Services which take care of draft persistence logic, in a similar manner you can create submissions using Forms Portal Submission services.
Please let me know your requirements, so that it can be worked upon accordingly.