Detect items

Is this an NxEquipements item?

if (api.isEquipment(item)) {
    // yes
}

Which piece is it?

api.readId(item).ifPresent(id -> {
    getLogger().info("set:   " + id.setId());
    getLogger().info("piece: " + id.pieceKey());
    getLogger().info("full:  " + id.asString());   // forest_warden:helmet
});

Get the full piece details

api.resolve(item).ifPresent(piece -> {
    getLogger().info("Name:  " + piece.displayName().orElse(piece.key()));
    getLogger().info("Slot:  " + piece.slotKey().orElse("?"));
    getLogger().info("Model: " + piece.customModelData());
});

Block a specific item from being dropped

@EventHandler
public void onDrop(PlayerDropItemEvent event) {
    ItemStack item = event.getItemDrop().getItemStack();
    api.readId(item).ifPresent(id -> {
        if (id.setId().equals("forest_warden")) {
            event.setCancelled(true);
            event.getPlayer().sendMessage("You cannot drop that.");
        }
    });
}

Count how many pieces of a set a player is wearing

public int wornFrom(Player player, String setId) {
    int count = 0;
    for (ItemStack piece : player.getInventory().getArmorContents()) {
        if (piece == null) continue;
        if (api.readId(piece).filter(id -> id.setId().equals(setId)).isPresent()) {
            count++;
        }
    }
    return count;
}

Reward a full set

if (wornFrom(player, "forest_warden") == 4) {
    player.addPotionEffect(new PotionEffect(PotionEffectType.REGENERATION, 100, 0, true, false));
}

What EquipmentId gives you