Lazy Singleton

Guice can inject instances as a singletons. Depending on the mode that Guice is in, it will lazily create the singletons (i.e. only when they are needed) or eagerly create them (i.e. when the Injector is created).

By default, Governator sets the Guice mode to Stage.PRODUCTION which causes singletons to be eager. Guice does not provide a lazy singleton scope. This is added by Governator.

LazySingleton

You can use lazy singleton either by annotating a class with @LazySingleton or using the LazySingletonScope when binding. E.g.

binder.bind(IFace.class).to(Impl.class).in(LazySingletonScope.get())

Example Usage

LazySingleton comes in handy when you need to have fine grained control over when an instance is created. You can do this by using a provider in conjunction with LazySingleton. E.g.

// an example class
@LazySingleton
public class MyClass
  ...

// inject a provider instead of the instance
public class Foo
{
  private final Provider<MyClass> myClassProvider;

  @Inject
  public foo(Provider<MyClass> myClassProvider)
  {
     this.myClassProvider = myClassProvider;
  }
  
  ...

  // somewhere else in the class
  myClassProvider.get();   // object will be created here
}