Guice

The Guice container

Concepts

A code example

IntroTest

Injectors and Guice

• Instances provided by injectors

public interface Injector{
	<T> T getInstance(Class<T> type)
	...
}

• Injectors created by the Guice static class

public final class Guice{
	static Injector createInjector(Module...)
}

Modules and bindings

• Injector creation is configured by modules

• A Module instance

  • is a binding collection
  • defined using a fluent interface

• Example

bind(Service.class).to(ServiceImpl.class);
bind(Integer.class).annotatedWith(Names.named(“timeout”))
	.toInstance(10);

• A Binding
  • maps types to their implementations
  • is polymorphic: linked bindings, instance bindings

Bindings

• Linked bindings

  • Allows for chaining

• Instance bindings

• Binding annotations

  • Example

• Provider bindings

  • Example

• @Provides annotated method bindings

  • Example

• Built-in bindings

  • Loggers
  • The injector

• Just-In-Time bindings

Scopes

• Scopes define the instance lifetime

  • Per injection
  • Per application (singleton)
  • Per session
  • Per request

• Example

Injections

• Constructor injection

  • Public no-arguments constructor
  • Constructor annotated with @Inject

• Method/setter injection

  • Annotated with @Inject
  • Allows for @Inject(optional=true)

• Field injection

• On demand field injection

• Example

anInjector.injectMembers(aPreviouslyCreatedInstance);

• Providing injection
  • Used for lazy or multiple instantiation

interface Provider<T>{
	T get();
}

ctor(Service1 svc, ...){
	// use svc instance
}
ctor(Provider<Service1> prov, ...){
	// use prov to create as many instances as necessary,
	// when necessary
}