A simpler and faster system for registering Bukkit event listeners in Java, Kotlin or Scala.

Events.java

import org.bukkit.Bukkit;
import org.bukkit.event.Event;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.HandlerList;
import org.bukkit.plugin.Plugin;
import org.bukkit.plugin.EventExecutor;
import java.util.function.Consumer;

public interface Events extends Listener, EventExecutor {
	static <T extends Event> Events listen(
			Plugin plugin,
			Class<T> type,
			Consumer<T> listener
	) { return listen(plugin, type, EventPriority.NORMAL, listener); }
	
	static <T extends Event> Events listen(
			Plugin plugin,
			Class<T> type,
			EventPriority priority,
			Consumer<T> listener
	) {
		final Events events = ($, event) -> listener.accept(type.cast(event));
		Bukkit.getPluginManager().registerEvent(type, events, priority, events, plugin);
		return events;
	}
	
	default void unregister() {
		HandlerList.unregisterAll(this);
	}
}

/* Usage Example
Events.listen(plugin, PlayerJoinEvent.class, event -> {
	//Event code here.
});
*/

Events.kt

import org.bukkit.Bukkit
import org.bukkit.event.Event
import org.bukkit.event.EventPriority
import org.bukkit.event.HandlerList
import org.bukkit.event.Listener
import org.bukkit.plugin.EventExecutor
import org.bukkit.plugin.Plugin

class EventListener(private val listener: Event.() -> Unit) : EventExecutor, Listener {
    override fun execute(ignored: Listener, event: Event) = listener(event)
    fun unregister() = HandlerList.unregisterAll(this)
}

inline fun <reified T : Event> listen(
        plugin: Plugin,
        priority: EventPriority = EventPriority.NORMAL,
        noinline listener: T.() -> Unit
) = EventListener(listener as Event.() -> Unit).also {
    Bukkit.getPluginManager().registerEvent(T::class.java, it, priority, it, plugin)
}

Events.scala

import java.util.function.Consumer

import org.bukkit.Bukkit
import org.bukkit.event.{Event, EventPriority, HandlerList, Listener}
import org.bukkit.plugin.{EventExecutor, Plugin}

trait Events[E <: Event] extends Listener with EventExecutor {
  def unregister(): Unit = HandlerList.unregisterAll(this)
}

object Events {

  def listen[E <: Event](
    plugin: Plugin,
    listener: Consumer[E],
    priority: EventPriority = EventPriority.NORMAL
  ): Events[E] = {
    val events: Events[E] = (_, event: E) => listener(event)
    Bukkit.getPluginManager.registerEvent(classOf[E], events, priority, events, plugin)
    events
  }
}