ItemStackとStringを相互変換する汎用メソッドです

ItemStringConverter.java

    //文字列をアイテムへ変換
    public static ItemStack stringToItem(String dataSt){
        String[] datas = dataSt.split("@@");

        Material mt = Material.getMaterial(datas[0]);
        int amount = 1;
        int damage = 0;

        try{
            amount = Integer.parseInt(datas[1]);
            damage = Integer.parseInt(datas[2]);
        }catch (NumberFormatException e){

        }

        Map<Enchantment, Integer> enchants = new HashMap<>();

        if(datas.length>=4&&!datas[3].equalsIgnoreCase("")){
            String[] datass = datas[3].split("&&");
            boolean isValue = false;
            Enchantment cash = null;
            for(String data : datass){
                if(!isValue){
                    cash = Enchantment.getByKey(NamespacedKey.minecraft(data));
                    isValue = true;
                }else{
                    int value = Integer.parseInt(data);
                    enchants.put(cash,value);
                    isValue = false;
                    cash = null;
                }
            }
        }

        String itName = "";

        if(datas.length>=5&&!datas[4].equalsIgnoreCase("")){
            itName = datas[4].replaceAll("_@_","@").replaceAll("_&_","&");
        }

        List<String> lore = new ArrayList<>();

        if(datas.length>=6&&!datas[5].equalsIgnoreCase("")){
            String[] datass = datas[5].split("&&");
            for(String data : datass){
                lore.add(data.replaceAll("_@_","@").replaceAll("_&_","&"));
            }
        }

        Set<ItemFlag> flags = new HashSet<>();

        if(datas.length>=7&&!datas[6].equalsIgnoreCase("")){
            String[] datass = datas[6].split("&&");
            for(String data : datass){
                flags.add(ItemFlag.valueOf(data));
            }
        }

        if(mt==null){
            return null;
        }

        ItemStack item = new ItemStack(mt,amount);
        ItemMeta meta = item.getItemMeta();
        if(meta==null){
            return null;
        }
        if (meta instanceof Damageable) {
            ((Damageable) meta).setDamage(damage);
        }
        for(Enchantment en : enchants.keySet()){
            int data = enchants.get(en);
            meta.addEnchant(en,data,false);
        }
        if(!itName.equalsIgnoreCase("")){
            meta.setDisplayName(itName);
        }
        meta.setLore(lore);
        for(ItemFlag flag : flags){
            meta.addItemFlags(flag);
        }
        item.setItemMeta(meta);
        return item;
    }

    //アイテムを文字列へ変換
    public static String itemToString(ItemStack item) {
        String mtName = "";
        int amount = 0;
        int damage = 0;
        Map<Enchantment, Integer> enchants = new HashMap<>();
        String itName = "";
        List<String> lore = new ArrayList<>();
        Set<ItemFlag> flags = null;


        ItemMeta meta = item.getItemMeta();

        Material mt = item.getType();
        mtName = mt.name();
        amount = item.getAmount();

        if(meta!=null){

            if (meta instanceof Damageable) {
                damage = ((Damageable) meta).getDamage();
            }

            if(meta.hasEnchants()){
                enchants =  meta.getEnchants();
            }

            if(meta.hasDisplayName()){
                itName = meta.getDisplayName();
            }

            if(meta.hasLore()){
                lore = meta.getLore();
            }

            flags = meta.getItemFlags();


        }


        StringBuilder resultSt = new StringBuilder(mtName + "@@" + amount + "@@" + damage + "@@");

        boolean first1 = true;
        for(Enchantment en : enchants.keySet()){
            if(!first1){
                resultSt.append("&&");
            }else{
                first1 = false;
            }
            int data = enchants.get(en);
            //namespacekey
            resultSt.append(en.getKey().getKey()).append("&&").append(data);
        }

        resultSt.append("@@").append(itName.replaceAll("&","_&_").replaceAll("@","_@_"))
                .append("@@");

        if(lore!=null){
            boolean first2 = true;
            for(String lor : lore){
                if(!first2){
                    resultSt.append("&&");
                }else{
                    first2 = false;
                }
                resultSt.append(lor.replaceAll("&","_&_").replaceAll("@","_@_"));
            }
        }

        resultSt.append("@@");


        if(flags!=null){
            boolean first3 = true;
            for(ItemFlag flag : flags){
                if(!first3){
                    resultSt.append("&&");
                }else{
                    first3 = false;
                }
                resultSt.append(flag.name());
            }
        }

        return resultSt.toString();
    }