This week's book giveaway is in the Agile and Other Processes forum. We're giving away four copies of Software Teaming: A Mob Programming, Whole-Team Approach and have Woody Zuill and Kevin Meadows on-line! See this thread for details.
There are some courses online, and of course a lot of other material. However - the best way to learn is through a practical, simple but non-trivial app. The official Spring reference is also a good place to start.
This particular course - to be clear - is not an intro so Spring. It doesn't assume a lot of Spring knowledge but it does assume some.
There are a number of books on Spring and lots of free tutorials and case studies on the Internet.
Spring in Action
Spring in Practice
are 3 paperback that I own.
Building a REST API with Spring 4 by Eugen is a step by step recipe e-book.
Search for "Java Spring" on Youtube and Google and get ready for a lot of viewing or reading.