My book Taming Thymeleaf is an in-depth guide to building a full web application using Spring Boot and Thymeleaf. You will learn how to efficiently build a web application taking into account validation, security, testing, etc.
I have published a book on InfoQ: Practical Guide to Building an API Back End with Spring Boot
See https://www.infoq.com/minibooks/spring-boot-building-api-backend for more information.
The book can be downloaded for free. Please consider a donation if you found the book helpful.