Registries

In the context of Minecraft, a registry holds onto a set of values of the same type, identifying each by a key. An example of such a registry would be the ItemType registry which holds all known item types. Registries are available via the RegistryAccess class.

While a large portion of registries are defined by the server and client independently, more and more are defined by the server and sent to the client while joining the server. This enables the server, and to that extent plugins, to define custom content for both itself and clients playing on it. Notable examples include enchantments and biomes.

To retrieve elements from a registry, their respective keys can be used. The API defines two types of keys.

• net.kyori.adventure.key.Key represents a namespace and a key.
• TypedKey wraps an Adventure key, but also includes the key of the registry the TypedKey belongs to.

An example of retrieving the Sharpness enchantment using TypedKeys looks as follows:

// Fetch the enchantment registry from the registry access
final Registry<Enchantment> enchantmentRegistry = RegistryAccess
    .registryAccess()
    .getRegistry(RegistryKey.ENCHANTMENT);

// Get the sharpness enchantment using its key.
// getOrThrow may be replaced with get if the registry may not contain said value
final Enchantment enchantment = enchantmentRegistry.getOrThrow(TypedKey.create(
    RegistryKey.ENCHANTMENT, Key.key("minecraft:sharpness"))
);

// Same as above, but using the instance's method
final Enchantment enchantment = enchantmentRegistry.getOrThrow(
    RegistryKey.ENCHANTMENT.typedKey(Key.key("minecraft:sharpness"))
);

// Same as above, but using generated create method
// available for data-driven registries or "writable" ones
// (those bound to a lifecycle event in RegistryEvents).
final Enchantment enchantment = enchantmentRegistry.getOrThrow(
    EnchantmentKeys.create(Key.key("minecraft:sharpness"))
);

// Same as above too, but using generated typed keys.
// Only Vanilla entries have generated keys, for custom entries, the above method must be used.
final Enchantment enchantment = enchantmentRegistry.getOrThrow(EnchantmentKeys.SHARPNESS);

Referencing entries in a registry is easier said then done. While for most cases a plain Collection of the values might suffice, alternative approaches are more often used by Minecraft and will hence be encountered.

A RegistrySet defines a collection of elements that relate to a registry.

Its most common subtype is the RegistryKeySet which simply holds onto TypedKey instances. An advantage of this data structure is its ability to remain valid even if the values of a registry change.

A RegistryKeySet can be created via the factory methods on RegistrySet like this:

// Create a new registry key set that holds a collection enchantments
final RegistryKeySet<Enchantment> bestEnchantments = RegistrySet.keySet(
    RegistryKey.ENCHANTMENT,
    // Arbitrary keys of enchantments to store in the key set.
    EnchantmentKeys.CHANNELING,
    EnchantmentKeys.create(Key.key("papermc:softspoon"))
);

A Tag follows up the concept of a RegistryKeySet but is itself named and can hence be referenced. A list of Vanilla tags can be found on the Minecraft wiki.

Beyond plain reading access to registries, Paper also offers a way for plugins to modify registries.

The general entrypoint for mutating registries is the RegistryEvents type, which provides an entry point for each registry that can be modified. Modification of a registry can take two different forms.

Creating new entries is done via the freeze lifecycle event on the respective registries. The freeze event is called right before a registry’s content is frozen in-place, meaning all Vanilla entries are registered. Plugins can hence register their own entries at this point. The following example shows how to create a new enchantment:

public class TestPluginBootstrap implements PluginBootstrap {

    @Override
    public void bootstrap(BootstrapContext context) {
        // Register a new handler for the freeze lifecycle event on the enchantment registry
        context.getLifecycleManager().registerEventHandler(RegistryEvents.ENCHANTMENT.freeze().newHandler(event -> {
            event.registry().register(
                // The key of the registry
                // Plugins should use their own namespace instead of minecraft or papermc
                EnchantmentKeys.create(Key.key("papermc:pointy")),
                b -> b.description(Component.text("Pointy"))
                    .supportedItems(event.getOrCreateTag(ItemTypeTagKeys.SWORDS))
                    .anvilCost(1)
                    .maxLevel(25)
                    .weight(10)
                    .minimumCost(EnchantmentRegistryEntry.EnchantmentCost.of(1, 1))
                    .maximumCost(EnchantmentRegistryEntry.EnchantmentCost.of(3, 1))
                    .activeSlots(EquipmentSlotGroup.ANY)
            );
        }));
    }
}

Modification of existing entries is useful for plugins that aim to change the way Vanilla entries behave. For this, use the entryAdd lifecycle event. The event is called for *any* entry added to a registry, however the API provides an easy way to target a specific entry for modification. The following example shows how to increase the maximum level of the Sharpness enchantment.

@Override
public void bootstrap(BootstrapContext context) {
    context.getLifecycleManager().registerEventHandler(RegistryEvents.ENCHANTMENT.entryAdd()
        // Increase the max level to 20
        .newHandler(event -> event.builder().maxLevel(20))
        // Configure the handler to only be called for the Vanilla sharpness enchantment.
        .filter(EnchantmentKeys.SHARPNESS)
    );
}