Keep code clean

Let’s imagine that you need to call a time-consuming service method from a controller and its result can be postponed. For example, it can import a huge number of records to a database and you can’t force the client to wait minutes/hours for a response. In such a case, it makes sense to make such a method asynchronous, i.e. a separate thread will be created to process the task, but the controller will immediately return to the user. Spring can easily help to configure asynchronous methods using @Async annotation.

Stateful authentication stores authentication sessions in some internal storage (in-memory, database, Redis, etc.) and returns a session identifier to a user.
In this tutorial, we’re going to cover stateless OAuth2 Google authentication when after a successful authentication a user receives an independent token (JWT in 99% of cases) with all required information in it. Both types of authentication have their own advantages and disadvantages. Stateless authentication is widely used for SPA applications and mobile clients.