@Override public synchronized void addOrder(OrderPO orderPO) { Logger.info("add order..."); try { List<OrderPO> orderPOs = getOrders(); orderPOs.add(orderPO); File file = SerializableFileHelper.getOrderFile(); try (ObjectOutputStream os = new ObjectOutputStream(new FileOutputStream(file))) { os.writeObject(orderPOs); } Logger.info("success"); } catch (IOException e) { Logger.error("fail"); Logger.error(e); } }