Trial by fire. We were in the infancy stages of a project and the alternative OTS options were really bad for our use case. We had a project manager that really believed in our group and pointed us to the Spring framework as one they had used in the past to solve a number of the same issues we were facing at the time. I had mainly worked in very heavy custom Java environments (no frameworks, and very few third-party dependencies) so dropping into a Framework with actual rules/guidelines was so nice and I’m currently noodling out how to rewrite some of our legacy apps in Spring because of how much it slots into our workflows.

I don’t love programming books and find them very hard to follow, so I leaned heavily on Baeldung and StackOverflow for most of my questions. Like some of the other comments in this thread, I had a hard time understanding dependency injection since I had no prior experience with it, but man-oh-man is it useful.

As someone who needs to understand the concepts first (instead of simply learning by doing), the guides by Marco Behler really helped. And the official documentation is great too!