https://github.com/google/guice/guice: Guice is a lightweight dependency injection framework for Java 6 and above (Google, Inc.) 
/*
 * 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;


An object capable of providing instances of type T. Providers are used in numerous ways by Guice: 
    

  • When the default means for obtaining instances (an injectable or parameterless constructor) is insufficient for a particular binding, the module can specify a custom Provider instead, to control exactly how Guice creates or obtains instances for the binding. 
  • An implementation class may always choose to have a Provider<T> instance injected, rather than having a T injected directly. This may give you access to multiple instances, instances you wish to safely mutate and discard, instances which are out of scope (e.g. using a @RequestScoped object from within a @SessionScoped object), or instances that will be initialized lazily. 
  • A custom Scope is implemented as a decorator of Provider<T>, which decides when to delegate to the backing provider and when to provide the instance some other way. 
  • The Injector offers access to the Provider<T> it uses to fulfill requests for a given key, via the Injector.getProvider methods. 


Author:crazybob@google.com (Bob Lee)
Type parameters:
  • <T> – the type of object this provides
/**
 * An object capable of providing instances of type {@code T}. Providers are used in numerous ways
 * by Guice:
 *
 * <ul>
 * <li>When the default means for obtaining instances (an injectable or parameterless constructor)
 *     is insufficient for a particular binding, the module can specify a custom {@code Provider}
 *     instead, to control exactly how Guice creates or obtains instances for the binding.
 * <li>An implementation class may always choose to have a {@code Provider<T>} instance injected,
 *     rather than having a {@code T} injected directly. This may give you access to multiple
 *     instances, instances you wish to safely mutate and discard, instances which are out of scope
 *     (e.g. using a {@code @RequestScoped} object from within a {@code @SessionScoped} object), or
 *     instances that will be initialized lazily.
 * <li>A custom {@link Scope} is implemented as a decorator of {@code Provider<T>}, which decides
 *     when to delegate to the backing provider and when to provide the instance some other way.
 * <li>The {@link Injector} offers access to the {@code Provider<T>} it uses to fulfill requests for
 *     a given key, via the {@link Injector#getProvider} methods.
 * </ul>
 *
 * @param <T> the type of object this provides
 * @author crazybob@google.com (Bob Lee)
 */
public interface Provider<T> extends javax.inject.Provider<T> {

  
Provides an instance of T. 
Throws:
  • OutOfScopeException – when an attempt is made to access a scoped object while the scope
    in question is not currently active
  • ProvisionException – if an instance cannot be provided. Such exceptions include messages
    and throwables to describe why provision failed.
/**
   * Provides an instance of {@code T}.
   *
   * @throws OutOfScopeException when an attempt is made to access a scoped object while the scope
   *     in question is not currently active
   * @throws ProvisionException if an instance cannot be provided. Such exceptions include messages
   *     and throwables to describe why provision failed.
   */
  @Override
  T get();
}