urldate in BibTeX gets ignored

Ideally, you'd be using a bibliography style file -- the argument of the \bibliographystyle command -- that is set to recognize and process a field named "lastvisited". Which style file are you currently using?

If you can't obtain a suitable style file (extension .bst) that processes the contents of a field named "lastvisited", you could pursue either of the following strategies:

• First, you might combine the contents of the note and lastvisited fields into a single note field, i.e., combine

  note = {\url{http://java.sun.com/products/jlf/ed1/dg/higq.htm}},
  lastvisited = {2012-03-20},
  

  into

  note = {\url{http://java.sun.com/products/jlf/ed1/dg/higq.htm}, visited 2012-03-20},
  

• Second, if you're using a reasonably modern bib style file (i.e., which recognizes a field named url), you could (i) change the label "note" to "url" and (ii) change the label "lastvisited" to "note" and add "visited on" to the contents of the new note field.

  url = {\url{http://java.sun.com/products/jlf/ed1/dg/higq.htm}},
  note = {visited on 2012-03-20},
  

  Addendum: Some examples of reasonably modern bib style files (i.e., which recognize a field named url) are those that come with the natbib package: plainnat.bst, unsrtnat.bst, and abbrvnat.bst. They behave very much like the plain, unsrt, and abbrv style files while recognizing five additional fields -- doi, eid, isbn, issn, and url -- beyond the 22+ fields recognized by the original bib style files plain, unsrt, and abbrv.

I ran into this thing too, so I changed the IEEEtran.bst file to include a urldate.

Currently it produces something like:

tex.stackexchange.com (Accessed March 4, 2016)

given:

@misc{example,
    url = {tex.stackexchange.com},
    urldate = {March 4, 2016}
}

Just search for "Accessed" in the file if you want to change that to some other phrase like "Last visited."