Working with Spring systematically, Eugene has given "Spring Puzzlers" talk earlier. Now he returns with new problems, nuances and tasks that require unusual solutions — but this time the talk will be more serious. It will cover specific situations, some of which you could meet in real projects, some will meet later, and then there are ones that can seem very esoteric — but they all come from real projects. We will talk mostly about spring-core, noticing the latest changes made by Spring 4.3. As usual, there will be deep dives, questions for the audience, prizes and a lot of livecoding!