Scrap the current approach since the site is updated via Javascript. You won't be able to just download the HTML and make it work.
However, a much easier approach (than using Selenium or a JS engine) would be to simply request the source data that the Javascript is using to update the page:
http://www.batstrading.com/json/bzx/book/IBM
It's perfectly valid JSON. Request that link with your HTTP client and parse the JSON using Jackson. This will yield very reliable results.
Disclaimer You need to make sure that what you are doing complies with the Terms of Service on the website you are using. Otherwise you subject yourself to legal issues.