ClassCastException with NMS and reflection

Question

I've been trying to use reflection with Net Minecraft Server classes since they are version dependent. I've made a class that emulates the PacketPlayOutWorldParticles, but I wanted to do more. Since I needed to make a Chest look open and so, first I made sure that the packet would work. Then I made this:

public class ChestReflection {
    // Reference
    // PacketPlayOutBlockAction packet = new PacketPlayOutBlockAction(new
    // BlockPosition(x, y, z), BlockChest, 1, 1);

    private Class<?> getNMSClass(String nmsClassString) throws ClassNotFoundException {
        String version = Bukkit.getServer().getClass().getPackage().getName().replace(".", ",").split(",")[3] + ".";
        String name = "net.minecraft.server." + version + nmsClassString;
        Class<?> nmsClass = Class.forName(name);
        return nmsClass;
    }

    private Object getConnection(Player player) throws SecurityException, NoSuchMethodException, NoSuchFieldException,
            IllegalArgumentException, IllegalAccessException, InvocationTargetException {
        Method getHandle = player.getClass().getMethod("getHandle");
        Object nmsPlayer = getHandle.invoke(player);
        Field conField = nmsPlayer.getClass().getField("playerConnection");
        Object con = conField.get(nmsPlayer);
        return con;
    }

    private Object getBlockPosition(Location loc)
            throws ClassNotFoundException, InstantiationException, IllegalAccessException, IllegalArgumentException,
            InvocationTargetException, NoSuchMethodException, SecurityException {
        Class<?> nmsBlockPosition = getNMSClass("BlockPosition");
        Object nmsBlockPositionInstance = nmsBlockPosition
                .getConstructor(new Class[] { Double.TYPE, Double.TYPE, Double.TYPE })
                .newInstance(new Object[] { loc.getX(), loc.getY(), loc.getZ() });

        return nmsBlockPositionInstance;
    }

    public void setChest(Player player, int open, Location loc) {
        try {
            Class<?> nmsBlockPositionClass = getNMSClass("BlockPosition");
            Object nmsBlockPos = getBlockPosition(loc);
            Class<?> nmsPacketBlockAction = getNMSClass("PacketPlayOutBlockAction");
            Class<?> nmsBlock = getNMSClass("Block");
            Object nmsChest = getNMSClass("Blocks").getField("Chest");
            Class<?> nmsPacket = getNMSClass("Packet");

            Object nmsPackInstance = nmsPacketBlockAction
                    .getConstructor(new Class[] { nmsBlockPositionClass, nmsBlock, Integer.TYPE, Integer.TYPE })
                    .newInstance(new Object[] { nmsBlockPos, nmsChest, Integer.valueOf(1), Integer.valueOf(open) });
            Method sendPacket = getConnection(player).getClass().getMethod("sendPacket", nmsPacket);
            sendPacket.invoke(new Object[] { nmsPackInstance });

        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | IllegalArgumentException
                | InvocationTargetException | NoSuchMethodException | SecurityException | NoSuchFieldException e) {
            e.printStackTrace();
        }
        // -this is the reference-
        new PacketPlayOutBlockAction(new BlockPosition(loc.getX(), loc.getY(), loc.getZ()), Blocks.CHEST, 1, 0);
    }

    public void setChestOpenForEveryone(int open, Location loc) {
        for (Player player : Bukkit.getOnlinePlayers()) {
            setChest(player, open, loc);
        }
    }
}

And at line 54, which is

newInstance(new Object[] { nmsBlockPos, nmsChest, Integer.valueOf(1), Integer.valueOf(open) });

it gives me an error:

Error: java.lang.IllegalArgumentException: java.lang.ClassCastException@61f9358b

And I don't actually know what is causing it. Also I have included the packet without reflection for reference.

Answer 1

nmsChest is of type java.lang.reflect.Field, not whatever.Block. To get the value of that field, you'll have to do something like this:

• if Blocks.CHEST is a enum value (or is it Blocks.Chest? you seem to have mixed them up):

  nmsChest = Enum.valueOf((Class<Enum>) getNMSClass("Blocks"), "CHEST");
  

• else if Blocks.CHEST is a static field (this also works for a enum value, but doesn't look as good):

  nmsChest = getNMSClass("Blocks").getField("CHEST").get(null);