So, depending on what kind of a developer you want to be, depends on what you should focus on, however some things receive certain results faster.
I do not love Vaadin, but playing around with this #Spring #Vaadin
stuff if you wanted to be a "primarily backend" web dev, it wouldn't be a bad place to start, you can avoid learning a lot of frontend stuff up front.
I'm playing with it now because I find getting a good frontend #AngularJS
setup to be a bit frustrating based on my current level of experience. Angular isn't really a problem so much as getting the rest of a frontend "