com.google.inject.Provider Maven / Gradle / Ivy
/**
* 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:
*
*
* - 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.
*
*
- An implementation class may always choose to have a {@code Provider
} 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.
*
* - A custom {@link Scope} is implemented as a decorator of {@code Provider
}, which decides
* when to delegate to the backing provider and when to provide the instance some other way.
*
* - The {@link Injector} offers access to the {@code Provider
} it uses to fulfill requests
* for a given key, via the {@link Injector#getProvider} methods.
*
*
* @param the type of object this provides
*
* @author [email protected] (Bob Lee)
*/
public interface Provider {
/**
* 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();
}