Resource confusion

I'm having trouble figuring out the best way of obtaining existing files
for my program to use.

My program, which is a game, wants to open an input file that drives the
game. Any number of input files may exist but they'll typically be stored
in the same directory, although the user may choose to put supplementary
input files in different directories. I provide a preference dialog where
the user can indicate the directory which will serve as the starting
point for the file chooser that selects the input file to be used in
playing the game.

The program needs to work when I am testing in Eclipse and it also needs
to work when the program is executing in a production environment. I
expect that it will run via Java Web Start, a JNLP file, and a jar. (I'm
using a self-signed test certificate for now and granting all-permissions
via the JNLP file.)

At the moment, my preferences dialog allows the user to choose a
directory (or a directory and a file) that will serve as the starting
point for the file chooser that will be used by the Open logic that opens
the input file. The value of that starting point is being correctly
stored by my program and can be changed successfully via the preferences
dialog. But I'm not having any luck actually obtaining the file via my
current code. Given that the file name may include accented letters, it
seems necessary to decode it with UTF-8 so my code proceeds as follows:

=========================================================================
String phraseListStartPoint = this.userPrefs.get
(PHRASE_LIST_STARTPOINT_KEY, PHRASE_LIST_STARTPOINT_VALUE);
URL phraseListURL = this.getClass().getResource(phraseListStartPoint);
String encodedFileName = null;
String decodedFileName = null;
try {
    encodedFileName = phraseListURL.getFile();
    decodedFileName = URLDecoder.decode(encodedFileName, "UTF-8");
    }
catch (NullPointerException npe_excp) {
     this.logger.logp(Level.WARNING, this.CLASS_NAME, METHOD_NAME,
"Phrase list URL, " + phraseListStartPoint + ", does not exist. Using
default directory instead.");
    }
catch (UnsupportedEncodingException ue_excp) {
    this.logger.logp(Level.WARNING, this.CLASS_NAME, METHOD_NAME,
"Failed to decode file name " + encodedFileName, ue_excp);
    System.exit(16);
    }

File startPoint = null;
if (decodedFileName != null) startPoint = new File(decodedFileName);
else startPoint = new File(System.getProperty("user.home"));

/* Launch the file chooser, open the file, read it..... */
=========================================================================

This code inevitably reveals that phraseListURL is null, even though the
value of PHRASE_LIST_STARTPOINT_VALUE is a path found on my file system
such as C:\Games\PhraseLists.

Clearly, this.getClass().getResource(phraseListStartPoint) is failing to
work as I would like.

I've tried reading the API on the getResource() method of the Class class
but I'm not following it. I know nothing about class loaders or which one
is the right one to use when. I'm not even sure I should be using an
approach like this to access a file that is in the file system.

I might bundle a few sample input files into the jar when I make this
game publicly accessible via Java Web Start but I mean those only to be
examples that players can use to build their own input files. Therefore,
I don't think they'll be accessing their own files from within the jar
but rather from the file system on their own computer. So I need the best
way to code the access to this file regardless of whether it is in a jar
or on the file system locally.

Can anyone get me going in the right direction on this? Maybe a few
general remarks about best practices and then suggestions on where to go
to find the exact techniques I'll need?

--
Novice