Event listeners

Every class of a Versatia plugin that implements Bukkit's Listener is registered when the plugin starts. There is no registerEvents call to write and nothing to annotate:

class WelcomeListener(private val greeter: Greeter) : Listener {
    @EventHandler
    fun onJoin(event: PlayerJoinEvent) = event.player.sendMessage(greeter.greeting())
}

ExampleVersatiaExample-Events-Listeners

A plain listener with an injected bean and a listener that is itself a bean, both registered automatically.

Open the repositoryStart with Listeners.kt

Which instance is registered

The listener is…	Registered instance
a bean (@LocalBean, @ExposeSingleton, …)	the bean itself; nothing is created twice
a plain class	a new instance, created like a bean: one constructor, parameters injected, @Qualifier honoured; it is not put into the container. Its @Value properties are set before it is registered and again at every reload. A class that is also a BackgroundTask is created once, and that instance both listens and runs
an object	the object
the plugin's main class	the plugin instance

Abstract classes and interfaces extending Listener are skipped. A plain listener class obeys the bean declaration rules: exactly one constructor, injectable parameters, no type parameters, no inner classes. Its dependencies are checked at compile time like a bean's.

When

Registration happens at PLUGIN_START_ONLY, once the plugin's beans exist and before its auto-invoked start functions run, so a start function may already fire events the plugin listens to. Bukkit unregisters every listener of a plugin when it is disabled; the runtime adds nothing to that.

Switching it off

ExampleVersatiaExample-Enhancements-FeatureSwitches

A base plugin class switching extraction off and a main class switching listener registration off.

Open the repositoryStart with SwitchesPlugin.kt

@DisableVersatiaFeatures(registerListeners = true)
class MyPlugin : VersatiaPlugin()

The plugin then registers its listeners itself, as any Bukkit plugin does. Every feature a plugin inherits and its switch are listed under Enhancements on a base class.

How it works

VersatiaPlugin carries @RegisterListeners, a subclass enhancement for Listener: the compile-time step records every matching class of the plugin as an element sent to RegisterListenersEnhancementProcessor (EventProcessors.REGISTER_LISTENERS), with VersatiaPlugin as the element's origin. The processor asks the plugin's BeanResolver for the instance first and instantiates only when there is no such bean.