hoge.java
String fileName = "hoge.mp3";
FileInputStream fis = null;
try {
fis = new FileInputStream(this.getFileStreamPath(fileName));
} catch (FileNotFoundException e) {
}
try {
mediaPlayer.setDataSource(fis.getFD());
mediaPlayer.prepare();
} catch (IllegalArgumentException e) {
} catch (IllegalStateException e) {
} catch (IOException e) {
}
mediaPlayer.start();