Trying to detect silence at the end of audio in mp3 format, well all formats would be useful but mp3 format is the most important
The only way I know of to reliably detect silence at the end of a sound clip is to convert it to a PCM format and do one of the following calculations checking for a certain minimum cut-off amplitude.
I've never managed to implement dB, but RMS is relatively simple, and should work for this use. I used it for the small bars seen on the lower left/right of trace area of the DukeBox player.
As to how to do any of that with MP3 format, see the details on the Java Sound info. page.