How to grant web app access to restricted file?
The first thing you need to do is discover which user owns the Tomcat process. You can do this by typing ps axu -w at the command line. The owner of the process will be in the first column. On a standard Mac install the web server (the process called httpd) is owned by the user _www. I assume Tomcat is owned by the same user.

Now change the ownership of the file so it is owned by _www and then you will be fine. Do this chown _www filename replacing filename of course.

Once you've done that you should be right.