I just passed my Spring 5 professional exam 3 weeks ago. It was very tough.
I had a headache after the exam.
For our exam guideline, checkout our posts in the certification result forum.
The books I read :
1. Getting Started With Spring Framework 5 (Great book, must read)
2. Spring In Action (4th and 5th edition) ( for more advanced info and read the chapter about Spring Boot Actuator)
3. Ivan Krizsan's Spring 5 tutorial on leanpub.com (I think it is free. I was happy to donate $20 to support Ivan)
1. Dominik Cebula's Spring tutorial on Udemy.com. He has 8 modules that will cover the exam topics. But so far, he has not finished module 4-8.
2. During the same time, you can check out John Thompson's Spring Framework Guru (Spring core 4, 5, Advanced Spring , Spring boot test).
Either itestjava or certification-questions
(They are just for practice. Don't try to remember the questions and answers.)
Google Spring boot test and Spring boot actuator. You will find some examples.
The exam has about 20% about these topics, which is new.
The book is not an official one. It was however written by somebody who is a Spring Certified professional and reviewed by a Spring trainer working for Panamsource which is a Pivotal partner.
I agree the exam is a little bit difficult without participating to an official course. But it is not impossible. I have received emails from people that have passed the Spring 5 certification exam by working with my previous book(which was writen for Spring 4) and filling up the gaps from the official Spring Documentation reference.
I can assume at this point the 2nd edition of the book, written for Spring 5 will be even more helpful.
Nonetheless Spring changes fast these days, so as long as you keep your eyes on the official Spring blog and the official Spring certification page and go throught the official study guide throughly, you should be fine.