public interface

Injector

com.google.inject.Injector

Class Overview

Builds the graphs of objects that make up your application. The injector tracks the dependencies for each type and uses bindings to inject them. This is the core of Guice, although you rarely interact with it directly. This "behind-the-scenes" operation is what distinguishes dependency injection from its cousin, the service locator pattern.

Contains several default bindings:

  • This Injector instance itself
  • A Provider<T> for each binding of type T
  • The java.util.logging.Logger for the class being injected
  • The Stage in which the Injector was created
Injectors are created using the facade class Guice.

An injector can also inject the dependencies of already-constructed instances. This can be used to interoperate with objects created by other frameworks or services.

Injectors can be hierarchical. Child injectors inherit the configuration of their parent injectors, but the converse does not hold.

The injector's internal bindings are available for introspection. This enables tools and extensions to operate on an injector reflectively.

Summary

Public Methods
abstract Injector createChildInjector(Module... modules)
Returns a new injector that inherits all state from this injector.
abstract Injector createChildInjector(Iterable<? extends Module> modules)
Returns a new injector that inherits all state from this injector.
abstract <T> List<Binding<T>> findBindingsByType(TypeLiteral<T> type)
Returns all explicit bindings for type.
abstract Map<Key<?>, Binding<?>> getAllBindings()
Returns a snapshot of this injector's bindings, both explicit and just-in-time.
abstract <T> Binding<T> getBinding(Key<T> key)
Returns the binding for the given injection key.
abstract <T> Binding<T> getBinding(Class<T> type)
Returns the binding for the given type.
abstract Map<Key<?>, Binding<?>> getBindings()
Returns this injector's explicit bindings.
abstract <T> Binding<T> getExistingBinding(Key<T> key)
Returns the binding if it already exists, or null if does not exist.
abstract <T> T getInstance(Key<T> key)
Returns the appropriate instance for the given injection key; equivalent to getProvider(key).get().
abstract <T> T getInstance(Class<T> type)
Returns the appropriate instance for the given injection type; equivalent to getProvider(type).get().
abstract <T> MembersInjector<T> getMembersInjector(TypeLiteral<T> typeLiteral)
Returns the members injector used to inject dependencies into methods and fields on instances of the given type T.
abstract <T> MembersInjector<T> getMembersInjector(Class<T> type)
Returns the members injector used to inject dependencies into methods and fields on instances of the given type T.
abstract Injector getParent()
Returns this injector's parent, or null if this is a top-level injector.
abstract <T> Provider<T> getProvider(Key<T> key)
Returns the provider used to obtain instances for the given injection key.
abstract <T> Provider<T> getProvider(Class<T> type)
Returns the provider used to obtain instances for the given type.
abstract Map<Class<? extends Annotation>, Scope> getScopeBindings()
Returns a map containing all scopes in the injector.
abstract Set<TypeConverterBinding> getTypeConverterBindings()
Returns a set containing all type converter bindings in the injector.
abstract void injectMembers(Object instance)
Injects dependencies into the fields and methods of instance.

Public Methods

public abstract Injector createChildInjector (Module... modules)

Returns a new injector that inherits all state from this injector. All bindings, scopes, interceptors and type converters are inherited -- they are visible to the child injector. Elements of the child injector are not visible to its parent.

Just-in-time bindings created for child injectors will be created in an ancestor injector whenever possible. This allows for scoped instances to be shared between injectors. Use explicit bindings to prevent bindings from being shared with the parent injector.

No key may be bound by both an injector and one of its ancestors. This includes just-in-time bindings. The lone exception is the key for Injector.class, which is bound by each injector to itself.

public abstract Injector createChildInjector (Iterable<? extends Module> modules)

Returns a new injector that inherits all state from this injector. All bindings, scopes, interceptors and type converters are inherited -- they are visible to the child injector. Elements of the child injector are not visible to its parent.

Just-in-time bindings created for child injectors will be created in an ancestor injector whenever possible. This allows for scoped instances to be shared between injectors. Use explicit bindings to prevent bindings from being shared with the parent injector. Optional injections in just-in-time bindings (created in the parent injector) may be silently ignored if the optional dependencies are from the child injector.

No key may be bound by both an injector and one of its ancestors. This includes just-in-time bindings. The lone exception is the key for Injector.class, which is bound by each injector to itself.

public abstract List<Binding<T>> findBindingsByType (TypeLiteral<T> type)

Returns all explicit bindings for type.

This method is part of the Guice SPI and is intended for use by tools and extensions.

public abstract Map<Key<?>, Binding<?>> getAllBindings ()

Returns a snapshot of this injector's bindings, both explicit and just-in-time. The returned map is immutable; it contains only the bindings that were present when getAllBindings() was invoked. Subsequent calls may return a map with additional just-in-time bindings.

The returned map does not include bindings inherited from a parent injector, should one exist.

This method is part of the Guice SPI and is intended for use by tools and extensions.

public abstract Binding<T> getBinding (Key<T> key)

Returns the binding for the given injection key. This will be an explicit bindings if the key was bound explicitly by a module, or an implicit binding otherwise. The implicit binding will be created if necessary.

This method is part of the Guice SPI and is intended for use by tools and extensions.

Throws
ConfigurationException if this injector cannot find or create the binding.

public abstract Binding<T> getBinding (Class<T> type)

Returns the binding for the given type. This will be an explicit bindings if the injection key was bound explicitly by a module, or an implicit binding otherwise. The implicit binding will be created if necessary.

This method is part of the Guice SPI and is intended for use by tools and extensions.

Throws
ConfigurationException if this injector cannot find or create the binding.

public abstract Map<Key<?>, Binding<?>> getBindings ()

Returns this injector's explicit bindings.

The returned map does not include bindings inherited from a parent injector, should one exist. The returned map is guaranteed to iterate (for example, with its entrySet() iterator) in the order of insertion. In other words, the order in which bindings appear in user Modules.

This method is part of the Guice SPI and is intended for use by tools and extensions.

public abstract Binding<T> getExistingBinding (Key<T> key)

Returns the binding if it already exists, or null if does not exist. Unlike getBinding(Key), this does not attempt to create just-in-time bindings for keys that aren't bound.

This method is part of the Guice SPI and is intended for use by tools and extensions.

public abstract T getInstance (Key<T> key)

Returns the appropriate instance for the given injection key; equivalent to getProvider(key).get(). When feasible, avoid using this method, in favor of having Guice inject your dependencies ahead of time.

Throws
ConfigurationException if this injector cannot find or create the provider.
ProvisionException if there was a runtime failure while providing an instance.

public abstract T getInstance (Class<T> type)

Returns the appropriate instance for the given injection type; equivalent to getProvider(type).get(). When feasible, avoid using this method, in favor of having Guice inject your dependencies ahead of time.

Throws
ConfigurationException if this injector cannot find or create the provider.
ProvisionException if there was a runtime failure while providing an instance.

public abstract MembersInjector<T> getMembersInjector (TypeLiteral<T> typeLiteral)

Returns the members injector used to inject dependencies into methods and fields on instances of the given type T.

Parameters
typeLiteral type to get members injector for
See Also

public abstract MembersInjector<T> getMembersInjector (Class<T> type)

Returns the members injector used to inject dependencies into methods and fields on instances of the given type T. When feasible, use getMembersInjector(TypeLiteral) instead to get increased up front error detection.

Parameters
type type to get members injector for
See Also

public abstract Injector getParent ()

Returns this injector's parent, or null if this is a top-level injector.

public abstract Provider<T> getProvider (Key<T> key)

Returns the provider used to obtain instances for the given injection key. When feasible, avoid using this method, in favor of having Guice inject your dependencies ahead of time.

Throws
ConfigurationException if this injector cannot find or create the provider.
See Also

public abstract Provider<T> getProvider (Class<T> type)

Returns the provider used to obtain instances for the given type. When feasible, avoid using this method, in favor of having Guice inject your dependencies ahead of time.

Throws
ConfigurationException if this injector cannot find or create the provider.
See Also

public abstract Map<Class<? extends Annotation>, Scope> getScopeBindings ()

Returns a map containing all scopes in the injector. The maps keys are scoping annotations like Singleton.class, and the values are scope instances, such as Scopes.SINGLETON. The returned map is immutable.

This method is part of the Guice SPI and is intended for use by tools and extensions.

public abstract Set<TypeConverterBinding> getTypeConverterBindings ()

Returns a set containing all type converter bindings in the injector. The returned set is immutable.

This method is part of the Guice SPI and is intended for use by tools and extensions.

public abstract void injectMembers (Object instance)

Injects dependencies into the fields and methods of instance. Ignores the presence or absence of an injectable constructor.

Whenever Guice creates an instance, it performs this injection automatically (after first performing constructor injection), so if you're able to let Guice create all your objects for you, you'll never need to use this method.

Parameters
instance to inject members on
See Also