It depends upon your design approach. As per MVC architecture a single servlet controls all actions. All html/jsp pages sends request to this controller servlet. For e.g Login page and registration page sends request to the same servlet. Based on the request type servlet performs the specific task and the response back to the client. So if the request type is registration it will be insert operation, if if is login it might be select queries. As far creating db/tables is concerned it should be done only once , so it should be in servlet init method.
Ideally you should create the database and required only once, and when creating you should always whether it exists or not. For learning purpose putting all queries in a single page is ok, however from real time perspective it's not. Think of a registration page it only needs to insert rows and no other operation is required here.