saveFileDialog showing file extensions in file chooser

I'm using the FileSaveService's saveFileDialog to save files in my webstart application. I'd really like to have the dialog show some possible extensions for the user to choose from. I'm saving some data as an Excel file, and I want to let the user choose "xls" as an extension. I've tried adding an array of strings as that parameter, and it doesn't do anything. In the javadocs, it says that this parameter might be ignored:

"extensions - A list of default extensions to show in the file chooser. For example, String[] { "txt", "java" }. These might be ignored by the JNLP Client."

I'm wondering if anyone knows why it gets ignored or under what circumstances it is ignored. I can't seem to find any information about it past those two sentences. What I'd really like to know if how I can tweak my program so that the extensionns won't be ignored, but I don't know if that's even possible. Or are there specific JNLP clients that never (or rarely) ignore the extensions? Thanks for any help! :)

[1027 byte] By [starlite182] at [2007-9-27 17:24:39]
# 1
Unfortunately, the current implementation of FileSaveDialog in Java Web Start allways ignores the extensions arg.
dietz at 2007-7-6 12:23:00 > top of Java-index,Desktop,Deploying...