Java tutorial
/** * Copyright (C) 2008 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.internal; import com.google.common.base.Objects; import com.google.common.base.Preconditions; import com.google.common.cache.Cache; import com.google.common.cache.CacheBuilder; import com.google.common.cache.RemovalCause; import com.google.common.cache.RemovalListener; import com.google.common.cache.RemovalNotification; import com.google.common.collect.LinkedHashMultiset; import com.google.common.collect.Maps; import com.google.common.collect.Multiset; import com.google.common.collect.Sets; import com.google.inject.Key; import com.google.inject.internal.util.SourceProvider; import java.lang.annotation.Annotation; import java.util.Map; import java.util.Set; /** * Minimal set that doesn't hold strong references to the contained keys. * * @author dweis@google.com (Daniel Weis) */ final class WeakKeySet { private Map<BlacklistKey, Multiset<Object>> backingMap; /** * This is already locked externally on add and getSources but we need it to handle clean up in * the evictionCache's RemovalListener. */ private final Object lock; /** * Tracks child injector lifetimes and evicts blacklisted keys/sources after the child injector is * garbage collected. */ private final Cache<State, Set<KeyAndSource>> evictionCache = CacheBuilder.newBuilder().weakKeys() .removalListener(new RemovalListener<State, Set<KeyAndSource>>() { @Override public void onRemoval(RemovalNotification<State, Set<KeyAndSource>> notification) { Preconditions.checkState(RemovalCause.COLLECTED.equals(notification.getCause())); cleanUpForCollectedState(notification.getValue()); } }).build(); /** * There may be multiple child injectors blacklisting a certain key so only remove the source * that's relevant. */ private void cleanUpForCollectedState(Set<KeyAndSource> keysAndSources) { synchronized (lock) { for (KeyAndSource keyAndSource : keysAndSources) { Multiset<Object> set = backingMap.get(keyAndSource.blacklistKey); if (set != null) { set.remove(keyAndSource.source); if (set.isEmpty()) { backingMap.remove(keyAndSource.blacklistKey); } } } } } WeakKeySet(Object lock) { this.lock = lock; } public void add(Key<?> key, State state, Object source) { if (backingMap == null) { backingMap = Maps.newHashMap(); } // if it's an instanceof Class, it was a JIT binding, which we don't // want to retain. if (source instanceof Class || source == SourceProvider.UNKNOWN_SOURCE) { source = null; } BlacklistKey blacklistKey = new BlacklistKey(key); Multiset<Object> sources = backingMap.get(blacklistKey); if (sources == null) { sources = LinkedHashMultiset.create(); backingMap.put(blacklistKey, sources); } Object convertedSource = Errors.convert(source); sources.add(convertedSource); // Avoid all the extra work if we can. if (state.parent() != State.NONE) { Set<KeyAndSource> keyAndSources = evictionCache.getIfPresent(state); if (keyAndSources == null) { evictionCache.put(state, keyAndSources = Sets.newHashSet()); } keyAndSources.add(new KeyAndSource(blacklistKey, convertedSource)); } } public boolean contains(Key<?> key) { evictionCache.cleanUp(); return backingMap != null && backingMap.containsKey(new BlacklistKey(key)); } public Set<Object> getSources(Key<?> key) { evictionCache.cleanUp(); Multiset<Object> sources = (backingMap == null) ? null : backingMap.get(new BlacklistKey(key)); return (sources == null) ? null : sources.elementSet(); } private static final class KeyAndSource { final BlacklistKey blacklistKey; final Object source; KeyAndSource(BlacklistKey blacklistKey, Object source) { this.blacklistKey = blacklistKey; this.source = source; } @Override public int hashCode() { return Objects.hashCode(blacklistKey, source); } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (!(obj instanceof KeyAndSource)) { return false; } KeyAndSource other = (KeyAndSource) obj; return Objects.equal(blacklistKey, other.blacklistKey) && Objects.equal(source, other.source); } } /** * The key for the Map is {@link Key} for most bindings, String for multibindings. * <p> * Reason being that multibinding Key's annotations hold a reference to their injector, implying * we'd leak memory. */ private static final class BlacklistKey { final Object delegate; BlacklistKey(Key<?> key) { // HACK: See comment on BlacklistKey for more info. This is tested in MultibinderTest, // MapBinderTest, and OptionalBinderTest in the multibinder test suite. if (isMultiBinderKey(key)) { delegate = key.toString(); } else { delegate = key; } } public boolean equals(Object obj) { if (obj instanceof BlacklistKey) { return delegate.equals(((BlacklistKey) obj).delegate); } else { return false; } } public int hashCode() { return delegate.hashCode(); } } /** * Returns {@code true} if the {@link Key} represents a multibound element. */ private static boolean isMultiBinderKey(Key<?> key) { Annotation annotation = key.getAnnotation(); return annotation != null // Can't depend on multibinder in core. && "com.google.inject.multibindings.RealElement".equals(annotation.getClass().getName()); } }