As someone who's just moved to Java myself... I suggest starting here: http://grails.org the Grails framework will get you started in Java based web development and you can learn more diving deeper into Java as you get more and more proficient. Grails is built on Spring which is a Java Enterprise platform but Grails saves you from having to learn all those "enterprisey" bits. Instead Grails picks defaults that are the most sensible for web development.
As you get better you can graduate to adding your own features to the framework or even beginning to use the more advanced Java frameworks outside Grails tying everything back together using Spring's IoC and Java JNDI. Or you can keep things light weight and web2.0 by using various remoting technologies inside Grails. It's a quick way to learn that doesn't put training wheels on you.
Get going in an afternoon... scale out using Java as your project grows.