dependency injection

Dependency injection

Winter uses Guice. PaperWinterPlugin creates the injector after module LOAD, using the platform bindings, discovered PluginModule instances, and the plugin itself as a Guice module.

Built-in bindings

The Paper boot module binds the current instance as WinterPlugin, Bukkit Plugin, and JavaPlugin; its SLF4J Logger; and the plugin data directory as a Path qualified with @DataFolder. ComponentModule binds accepted component classes as singletons and exposes ComponentManager and ReloadServiceManager.

@Component
public final class MessageStore {
  private final Path dataFolder;

  @Inject
  public MessageStore(@DataFolder final Path dataFolder) {
    this.dataFolder = dataFolder;
  }
}

@Component on a class binds its concrete type. An interface needs an additional binding. Options include a PluginModule.configure method, @Primary on an implementation, a Guice provider, or an exposed external contract.

Bind an interface

@Primary on a component links an interface to its implementation. By default it chooses the first directly implemented interface; specify the intended interface when there is more than one:

@Component
@Primary(ProfileRepository.class)
public final class SqlProfileRepository implements ProfileRepository {
}

For custom setup, implement PluginModule.configure(Binder) or override PaperWinterPlugin.configure(Binder). Avoid declaring the same interface binding through multiple routes; Guice rejects duplicate explicit bindings.

Providers

A provider component can directly implement com.google.inject.Provider<T>. The provider handler reads its declared Provider<T> interface and binds T through that provider:

@Component
public final class TokenProvider implements Provider<Token> {
  @Override
  public Token get() {
    return new Token();
  }
}

The current component handler expects Provider<T> to be declared directly on that class. The old @ProviderComponent annotation is a deprecated component stereotype that explicitly selects the handler.

Injection timing

Plugin and module member injection happens after Guice.createInjector. Accepted components are instantiated in the component INJECTION phase during module ENABLE. Do not request plugin.getInjector() in onPluginLoad, module onLoad, LOAD conditions, or LOAD admission decisions. Runtime @FileName YAML bindings and @Expose/@External links are described in Configuration and Exposed APIs and multi-module builds.