Использовать Apache Commons IO
FileUtils.writeByteArrayToFile(new File("pathname"), myByteArray)
Или, если вы настаиваете на выполнении работы для себя ...
try (FileOutputStream fos = new FileOutputStream("pathname")) {
fos.write(myByteArray);
//fos.close(); There is no more need for this line since you had created the instance of "fos" inside the try. And this will automatically close the OutputStream
}