Yeah it helps to know a little Java to get it up and running, but you just need a little glue to get Rhino talking to the servlet and vice versa.
Plus if you want to use the Java libraries from JavaScript you at least need to be familiar with the APIs (or know how to look them up in the javadocs)
Take a look at Helma if you don't want to deal with all that, it uses Rhino: http://helma.org/
I don't have any particular recommendations for Java books, probably any of the usual "learn java" style books are ok, it's not a particularly difficult language to learn the basics, but I'd check reviews of books on Amazon or something.
Plus if you want to use the Java libraries from JavaScript you at least need to be familiar with the APIs (or know how to look them up in the javadocs)
Take a look at Helma if you don't want to deal with all that, it uses Rhino: http://helma.org/