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Java example source code file (Injector.java)

This example Java source code file (Injector.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

annotation, binding, injector, list, map, membersinjector, module, provider, scope, set, util

The Injector.java Java example source code

/**
 * Copyright (C) 2006 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject;

import com.google.inject.spi.TypeConverterBinding;

import java.lang.annotation.Annotation;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * 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.
 *
 * <p>Contains several default bindings:
 *
 * <ul>
 * <li>This {@link Injector} instance itself
 * <li>A {@code Provider} for each binding of type {@code T}
 * <li>The {@link java.util.logging.Logger} for the class being injected
 * <li>The {@link Stage} in which the Injector was created
 * </ul>
 *
 * Injectors are created using the facade class {@link Guice}.
 *
 * <p>An injector can also {@link #injectMembers(Object) inject the dependencies} of
 * already-constructed instances. This can be used to interoperate with objects created by other
 * frameworks or services.
 *
 * <p>Injectors can be {@link #createChildInjector(Iterable) hierarchical}. Child injectors inherit
 * the configuration of their parent injectors, but the converse does not hold.
 *
 * <p>The injector's {@link #getBindings() internal bindings} are available for introspection. This
 * enables tools and extensions to operate on an injector reflectively.
 *
 * @author crazybob@google.com (Bob Lee)
 * @author jessewilson@google.com (Jesse Wilson)
 */
public interface Injector {

  /**
   * Injects dependencies into the fields and methods of {@code instance}. Ignores the presence or
   * absence of an injectable constructor.
   *
   * <p>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.
   *
   * @param instance to inject members on
   *
   * @see Binder#getMembersInjector(Class) for a preferred alternative that supports checks before
   *  run time
   */
  void injectMembers(Object instance);

  /**
   * Returns the members injector used to inject dependencies into methods and fields on instances
   * of the given type {@code T}.
   *
   * @param typeLiteral type to get members injector for
   * @see Binder#getMembersInjector(TypeLiteral) for an alternative that offers up front error
   *  detection
   * @since 2.0
   */
  <T> MembersInjector getMembersInjector(TypeLiteral typeLiteral);

  /**
   * Returns the members injector used to inject dependencies into methods and fields on instances
   * of the given type {@code T}. When feasible, use {@link Binder#getMembersInjector(TypeLiteral)}
   * instead to get increased up front error detection.
   *
   * @param type type to get members injector for
   * @see Binder#getMembersInjector(Class) for an alternative that offers up front error
   *  detection
   * @since 2.0
   */
  <T> MembersInjector getMembersInjector(Class type);

  /**
   * Returns this injector's <strong>explicit bindings.
   *
   * <p>The returned map does not include bindings inherited from a {@link #getParent() parent
   * injector}, should one exist. The returned map is guaranteed to iterate (for example, with
   * its {@link Map#entrySet()} iterator) in the order of insertion. In other words, the order in
   * which bindings appear in user Modules.
   *
   * <p>This method is part of the Guice SPI and is intended for use by tools and extensions.
   */
  Map<Key> getBindings();

  /**
   * Returns a snapshot of this injector's bindings, <strong>both explicit and
   * just-in-time</strong>. The returned map is immutable; it contains only the bindings that were
   * present when {@code getAllBindings()} was invoked. Subsequent calls may return a map with
   * additional just-in-time bindings.
   *
   * <p>The returned map does not include bindings inherited from a {@link #getParent() parent
   * injector}, should one exist.
   *
   * <p>This method is part of the Guice SPI and is intended for use by tools and extensions.
   * 
   * @since 3.0
   */
  Map<Key> getAllBindings();

  /**
   * 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.
   *
   * <p>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.
   */
  <T> Binding getBinding(Key key);

  /**
   * 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.
   *
   * <p>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.
   * @since 2.0
   */
  <T> Binding getBinding(Class type);
  
  /**
   * Returns the binding if it already exists, or null if does not exist. Unlike
   * {@link #getBinding(Key)}, this does not attempt to create just-in-time bindings
   * for keys that aren't bound.
   * 
   * <p> This method is part of the Guice SPI and is intended for use by tools and extensions.
   * 
   * @since 3.0
   */
  <T> Binding getExistingBinding(Key key);  

  /**
   * Returns all explicit bindings for {@code type}.
   *
   * <p>This method is part of the Guice SPI and is intended for use by tools and extensions.
   */
  <T> List> findBindingsByType(TypeLiteral type);

  /**
   * 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 Binder#getProvider(Key) for an alternative that offers up front error detection
   */
  <T> Provider getProvider(Key key);

  /**
   * 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 Binder#getProvider(Class) for an alternative that offers up front error detection
   */
  <T> Provider getProvider(Class type);

  /**
   * Returns the appropriate instance for the given injection key; equivalent to {@code
   * 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.
   * @throws ProvisionException if there was a runtime failure while providing an instance.
   */
  <T> T getInstance(Key key);

  /**
   * Returns the appropriate instance for the given injection type; equivalent to {@code
   * 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.
   * @throws ProvisionException if there was a runtime failure while providing an instance.
   */
  <T> T getInstance(Class type);

  /**
   * Returns this injector's parent, or {@code null} if this is a top-level injector.
   *
   * @since 2.0
   */
  Injector getParent();

  /**
   * 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.
   *
   * <p>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.
   *
   * <p>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 {@code Injector.class}, which is bound by each
   * injector to itself.
   *
   * @since 2.0
   */
  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.
   *
   * <p>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.
   *
   * <p>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 {@code Injector.class}, which is bound by each
   * injector to itself.
   *
   * @since 2.0
   */
  Injector createChildInjector(Module... modules);

  /**
   * Returns a map containing all scopes in the injector. The maps keys are scoping annotations
   * like {@code Singleton.class}, and the values are scope instances, such as {@code
   * Scopes.SINGLETON}. The returned map is immutable.
   *
   * <p>This method is part of the Guice SPI and is intended for use by tools and extensions.
   * 
   * @since 3.0
   */
  Map<Class getScopeBindings();

  /**
   * Returns a set containing all type converter bindings in the injector. The returned set is
   * immutable.
   *
   * <p>This method is part of the Guice SPI and is intended for use by tools and extensions.
   * 
   * @since 3.0
   */
  Set<TypeConverterBinding> getTypeConverterBindings();
}

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