How to use BukkitInput/Output stream?

I've been trying to figure out this code for three days now (and I haven't even been working on the rest of the plugin for three days). Can't find much information about these classes and how to bug fix them.

Code:

    public static Inventory loadInventory(String s) {

        File invFile = new File(s);
        Inventory newInv = Bukkit.createInventory(null, 9);

        if (invFile.exists()) {
            try (BukkitObjectInputStream bois = new BukkitObjectInputStream(new FileInputStream(invFile))) {
                while (true) {
                    newInv.addItem((ItemStack) bois.readObject());
                }
            } catch (OptionalDataException e) {
                e.printStackTrace();
            } catch (EOFException e) {
                return newInv;
            } catch (ClassNotFoundException | IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    public static void saveInventory(Inventory i, String s) {
        File invFile = new File(s);

        if (!invFile.exists()) {
            try {
                invFile.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(invFile));
            BukkitObjectOutputStream boos = new BukkitObjectOutputStream(oos);
            for (ItemStack is : i.getContents()) {
                if (is == null)
                    continue;
                boos.writeObject(is);
            }
            boos.flush();
            boos.close();
            oos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

Always returns OptionalDataException and I can't figure out why. The error message points it back to this line

Code:

newInv.addItem((ItemStack) bois.readObject());

Even if I don't apply the ItemStack cast. Even if I just try printing the object to the console, I still receive the error message. Any help is appreciated, thanks in advance.

 

@gelloe Could you show the code where you implement/run the methods?

 

Nvm, I got the code working with help from a few other libraries. Here's the code in case anyone is interested:

Code:

    public static String saveInventory(Inventory inv, int size) {
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        try (final BukkitObjectOutputStream data = new BukkitObjectOutputStream(stream)) {
            data.writeInt(size);
            for (int i = 0; i < inv.getSize(); i++) {
                data.writeObject(inv.getItem(i));
            }
            data.flush();
            data.close();
            return Base64.getEncoder().encodeToString(stream.toByteArray());
        } catch (final IOException e) {
            e.printStackTrace();
        }
        return null;
    }
   
    public static String encodeItems(ArrayList<ItemStack> items) {
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        try (final BukkitObjectOutputStream data = new BukkitObjectOutputStream(stream)) {
            data.writeInt(items.size());
            for (ItemStack i : items)
                data.writeObject(i);
            data.flush();
            data.close();
            return Base64.getEncoder().encodeToString(stream.toByteArray());
        } catch (final IOException e) {
            e.printStackTrace();
        }
        return null;
    }