How to make a text file to be the "database" in a Spring Rest Application?

I´m developing a Jokenpo Game using React with Spring Rest, but I can´t have a database to store all the information needed(create and delete moves, create and delete players).

I don´t know the best practice of development, or if there is some design pattern on how to store that kind of information. I know there is the folder src/main/resources where maybe I can store a text file there and thought about on the startup of the api it loads that file with the begin of the game, maybe, and after changing it during the game.

Trying to be more clear: I just would like to know the simplest way of storing information without being a database inside of a Spring Rest application. I really appreciate any helps. Thanks.