fine

src/main/java/eu/m724/musicPlugin/item/ItemStorage.java

@@ -24,6 +24,7 @@ public class ItemStorage {
     public static void init(MusicPlugin plugin) {
         INSTANCE = new ItemStorage();
         INSTANCE.directory = new File(plugin.getDataFolder(), "storage");
+        INSTANCE.directory.mkdir();
     }
 
     static ItemStorage getInstance() {
@@ -31,7 +32,7 @@ public class ItemStorage {
     }
 
     public PortableMediaPlayer getPortableMediaPlayer(int id) throws IOException {
-        var file = new File(directory, HexFormat.of().toHexDigits(id));
+        var file = new File(directory, HexFormat.of().toHexDigits(id) + ".pmpdata.bin");
 
         if (!file.exists()) return null;
 
@@ -43,7 +44,7 @@ public class ItemStorage {
 
         var premium = buffer.get() == 1;
 
-        var eb = new byte[Byte.toUnsignedInt(buffer.get())];
+        var eb = new byte[buffer.get() & 0xFF];
         buffer.get(eb);
         var engraving = new String(eb, StandardCharsets.UTF_8);
 
@@ -51,7 +52,7 @@ public class ItemStorage {
     }
 
     public void savePortableMediaPlayer(PortableMediaPlayer player) throws IOException {
-        var file = new File(directory, HexFormat.of().toHexDigits(player.id));
+        var file = new File(directory, HexFormat.of().toHexDigits(player.id) + ".pmpdata.bin");
 
         Files.write(file.toPath(), getData(player));
     }

src/main/java/eu/m724/musicPlugin/item/PortableMediaPlayer.java

@@ -50,6 +50,7 @@ public class PortableMediaPlayer {
         var is = new ItemStack(Material.IRON_INGOT);
         var meta = is.getItemMeta();
 
+        meta.setItemName("Portable music player");
         meta.addEnchant(Enchantment.UNBREAKING, 1, false);
         meta.addItemFlags(ItemFlag.HIDE_ENCHANTS);
         meta.getPersistentDataContainer().set(namespacedKey, PersistentDataType.INTEGER, id);