If I wanted to learn more about web development in Java, what's a good starting point? Something that can give me a high-level overview, current best practices, and perhaps a simple "Hello World" example.

I currently work with Django and Wordpress, so I'm not totally new here. But last time I dived into this world, I could not make heads or tails of it.

Java seems like a powerful tool to have in your toolbox, but from what I've found it does not lend itself to be easily picked up.