| /** |
| * 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 {@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> { |
| |
| /** |
| * Provides an instance of {@code T}. Must never return {@code null}. |
| * |
| * @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. |
| */ |
| T get(); |
| } |