Modern API Development with Spring and Spring Boot, published by Packt

Go further into "Learn Spring Security":

A small Java library for producing nice looking text-based line-graphs and tables.

📚 Freely available programming books

Design patterns implemented in Java

Interactive roadmaps, guides and other educational content to help developers grow in their careers.

https://start.spring.io

Open Source Identity and Access Management For Modern Applications and Services

CloudFoundry User Account and Authentication (UAA) Server