We have both print and online resources for bible commentaries. To find books on an individual book of the Bible, use OneSearch. Try a general keyword search like the following, and then under "Resource Type" on the left, choose "books":
john AND bible AND commentaries
You can find these additional print and/or online commentaries in OneSearch.
The Anchor Bible Dictionary by 
A Dictionary of Biblical Interpretation by 
The HarperCollins Bible Dictionary by 
The New Jerome Biblical Commentary by The HarperCollins Bible Dictionary by These are some additional resources that can be helpful when you're doing Bible research.
Resources for Biblical Studies - William G. Squires Library
