JLayer

http://www.javazoom.net/javalayer/javalayer.html
JavaからMP3を扱うことができるライブラリ。音を鳴らすだけなら、↓みたいな感じに書けばOKらしい。

FileInputStream ins = new FileInputStream("gunbuster.mp3");
AudioDevice device = FactoryRegistry.systemRegistry().createAudioDevice();
Player player = new Player(ins, device);
player.play();