This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
The first thing I would do is pick a Java web application framework: JSF, Spring MVC, Struts 2, etc. etc. etc. (there are a million of them). Once you have the framework you can recreate the web pages using the framework. For some of the backing code you might be able to simply rename the source files from .cs to .java and fix up the errors by finding which Java class to use (as one person put it to me way back in 2001: ".NET is Java run through a thesaurus."). Also, try searching for C# to Java converters; I image you will find a few. (I used a Java to C# converter ages ago, it did a lot of the grunt work and left me to work out the more difficult things, but it did help a lot.)