| /** |
| * 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.internal.CircularDependencyProxy; |
| import com.google.inject.internal.InternalInjectorCreator; |
| import com.google.inject.internal.LinkedBindingImpl; |
| import com.google.inject.spi.BindingScopingVisitor; |
| import com.google.inject.spi.ExposedBinding; |
| |
| import java.lang.annotation.Annotation; |
| |
| /** |
| * Built-in scope implementations. |
| * |
| * @author crazybob@google.com (Bob Lee) |
| */ |
| public class Scopes { |
| |
| private Scopes() {} |
| |
| /** A sentinel value representing null. */ |
| private static final Object NULL = new Object(); |
| |
| /** |
| * One instance per {@link Injector}. Also see {@code @}{@link Singleton}. |
| */ |
| public static final Scope SINGLETON = new Scope() { |
| public <T> Provider<T> scope(final Key<T> key, final Provider<T> creator) { |
| return new Provider<T>() { |
| /* |
| * The lazily initialized singleton instance. Once set, this will either have type T or will |
| * be equal to NULL. |
| */ |
| private volatile Object instance; |
| |
| // DCL on a volatile is safe as of Java 5, which we obviously require. |
| @SuppressWarnings("DoubleCheckedLocking") |
| public T get() { |
| if (instance == null) { |
| /* |
| * Use a pretty coarse lock. We don't want to run into deadlocks |
| * when two threads try to load circularly-dependent objects. |
| * Maybe one of these days we will identify independent graphs of |
| * objects and offer to load them in parallel. |
| * |
| * This block is re-entrant for circular dependencies. |
| */ |
| synchronized (InternalInjectorCreator.class) { |
| if (instance == null) { |
| T provided = creator.get(); |
| |
| // don't remember proxies; these exist only to serve circular dependencies |
| if (provided instanceof CircularDependencyProxy) { |
| return provided; |
| } |
| |
| Object providedOrSentinel = (provided == null) ? NULL : provided; |
| if (instance != null && instance != providedOrSentinel) { |
| throw new ProvisionException( |
| "Provider was reentrant while creating a singleton"); |
| } |
| |
| instance = providedOrSentinel; |
| } |
| } |
| } |
| |
| Object localInstance = instance; |
| // This is safe because instance has type T or is equal to NULL |
| @SuppressWarnings("unchecked") |
| T returnedInstance = (localInstance != NULL) ? (T) localInstance : null; |
| return returnedInstance; |
| } |
| |
| public String toString() { |
| return String.format("%s[%s]", creator, SINGLETON); |
| } |
| }; |
| } |
| |
| @Override public String toString() { |
| return "Scopes.SINGLETON"; |
| } |
| }; |
| |
| /** |
| * No scope; the same as not applying any scope at all. Each time the |
| * Injector obtains an instance of an object with "no scope", it injects this |
| * instance then immediately forgets it. When the next request for the same |
| * binding arrives it will need to obtain the instance over again. |
| * |
| * <p>This exists only in case a class has been annotated with a scope |
| * annotation such as {@link Singleton @Singleton}, and you need to override |
| * this to "no scope" in your binding. |
| * |
| * @since 2.0 |
| */ |
| public static final Scope NO_SCOPE = new Scope() { |
| public <T> Provider<T> scope(Key<T> key, Provider<T> unscoped) { |
| return unscoped; |
| } |
| @Override public String toString() { |
| return "Scopes.NO_SCOPE"; |
| } |
| }; |
| |
| /** |
| * Returns true if {@code binding} is singleton-scoped. If the binding is a {@link |
| * com.google.inject.spi.LinkedKeyBinding linked key binding} and belongs to an injector (ie. it |
| * was retrieved via {@link Injector#getBinding Injector.getBinding()}), then this method will |
| * also true if the target binding is singleton-scoped. |
| * |
| * @since 3.0 |
| */ |
| public static boolean isSingleton(Binding<?> binding) { |
| do { |
| boolean singleton = binding.acceptScopingVisitor(new BindingScopingVisitor<Boolean>() { |
| public Boolean visitNoScoping() { |
| return false; |
| } |
| |
| public Boolean visitScopeAnnotation(Class<? extends Annotation> scopeAnnotation) { |
| return scopeAnnotation == Singleton.class |
| || scopeAnnotation == javax.inject.Singleton.class; |
| } |
| |
| public Boolean visitScope(Scope scope) { |
| return scope == Scopes.SINGLETON; |
| } |
| |
| public Boolean visitEagerSingleton() { |
| return true; |
| } |
| }); |
| |
| if (singleton) { |
| return true; |
| } |
| |
| if (binding instanceof LinkedBindingImpl) { |
| LinkedBindingImpl<?> linkedBinding = (LinkedBindingImpl) binding; |
| Injector injector = (Injector) linkedBinding.getInjector(); |
| if (injector != null) { |
| binding = injector.getBinding(linkedBinding.getLinkedKey()); |
| continue; |
| } |
| } else if(binding instanceof ExposedBinding) { |
| ExposedBinding<?> exposedBinding = (ExposedBinding)binding; |
| Injector injector = exposedBinding.getPrivateElements().getInjector(); |
| if (injector != null) { |
| binding = injector.getBinding(exposedBinding.getKey()); |
| continue; |
| } |
| } |
| |
| return false; |
| } while (true); |
| } |
| } |