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Java example source code file (Multibinder.java)

This example Java source code file (Multibinder.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, binding, class, element, key, list, multibinder, override, permitduplicatesmodule, realmultibinder, reflection, set, string, suppresswarnings, typeliteral, util

The Multibinder.java Java example source code

/**
 * 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.multibindings;

import static com.google.common.base.Predicates.equalTo;
import static com.google.common.primitives.Ints.MAX_POWER_OF_TWO;
import static com.google.common.collect.Iterables.filter;
import static com.google.common.collect.Iterables.getOnlyElement;
import static com.google.inject.multibindings.Element.Type.MULTIBINDER;
import static com.google.inject.name.Names.named;

import com.google.common.base.Objects;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;
import com.google.inject.AbstractModule;
import com.google.inject.Binder;
import com.google.inject.Binding;
import com.google.inject.ConfigurationException;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.Provider;
import com.google.inject.TypeLiteral;
import com.google.inject.binder.LinkedBindingBuilder;
import com.google.inject.internal.Errors;
import com.google.inject.spi.BindingTargetVisitor;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.HasDependencies;
import com.google.inject.spi.Message;
import com.google.inject.spi.ProviderInstanceBinding;
import com.google.inject.spi.ProviderWithDependencies;
import com.google.inject.spi.ProviderWithExtensionVisitor;
import com.google.inject.spi.Toolable;
import com.google.inject.util.Types;

import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * An API to bind multiple values separately, only to later inject them as a
 * complete collection. Multibinder is intended for use in your application's
 * module:
 * <pre>
 * public class SnacksModule extends AbstractModule {
 *   protected void configure() {
 *     Multibinder<Snack> multibinder
 *         = Multibinder.newSetBinder(binder(), Snack.class);
 *     multibinder.addBinding().toInstance(new Twix());
 *     multibinder.addBinding().toProvider(SnickersProvider.class);
 *     multibinder.addBinding().to(Skittles.class);
 *   }
 * }</code>
* * <p>With this binding, a {@link Set}{@code } can now be injected: * <pre> * class SnackMachine { * {@literal @}Inject * public SnackMachine(Set<Snack> snacks) { ... } * }</code> * * If desired, {@link Collection}{@code <Provider} can also be injected. * * <p>Contributing multibindings from different modules is supported. For * example, it is okay for both {@code CandyModule} and {@code ChipsModule} * to create their own {@code Multibinder<Snack>}, and to each contribute * bindings to the set of snacks. When that set is injected, it will contain * elements from both modules. * * <p>The set's iteration order is consistent with the binding order. This is * convenient when multiple elements are contributed by the same module because * that module can order its bindings appropriately. Avoid relying on the * iteration order of elements contributed by different modules, since there is * no equivalent mechanism to order modules. * * <p>The set is unmodifiable. Elements can only be added to the set by * configuring the multibinder. Elements can never be removed from the set. * * <p>Elements are resolved at set injection time. If an element is bound to a * provider, that provider's get method will be called each time the set is * injected (unless the binding is also scoped). * * <p>Annotations are be used to create different sets of the same element * type. Each distinct annotation gets its own independent collection of * elements. * * <p>Elements must be distinct. If multiple bound elements * have the same value, set injection will fail. * * <p>Elements must be non-null. If any set element is null, * set injection will fail. * * @author jessewilson@google.com (Jesse Wilson) */ public abstract class Multibinder<T> { private Multibinder() {} /** * Returns a new multibinder that collects instances of {@code type} in a {@link Set} that is * itself bound with no binding annotation. */ public static <T> Multibinder newSetBinder(Binder binder, TypeLiteral type) { return newRealSetBinder(binder, Key.get(type)); } /** * Returns a new multibinder that collects instances of {@code type} in a {@link Set} that is * itself bound with no binding annotation. */ public static <T> Multibinder newSetBinder(Binder binder, Class type) { return newRealSetBinder(binder, Key.get(type)); } /** * Returns a new multibinder that collects instances of {@code type} in a {@link Set} that is * itself bound with {@code annotation}. */ public static <T> Multibinder newSetBinder( Binder binder, TypeLiteral<T> type, Annotation annotation) { return newRealSetBinder(binder, Key.get(type, annotation)); } /** * Returns a new multibinder that collects instances of {@code type} in a {@link Set} that is * itself bound with {@code annotation}. */ public static <T> Multibinder newSetBinder( Binder binder, Class<T> type, Annotation annotation) { return newRealSetBinder(binder, Key.get(type, annotation)); } /** * Returns a new multibinder that collects instances of {@code type} in a {@link Set} that is * itself bound with {@code annotationType}. */ public static <T> Multibinder newSetBinder(Binder binder, TypeLiteral type, Class<? extends Annotation> annotationType) { return newRealSetBinder(binder, Key.get(type, annotationType)); } /** * Returns a new multibinder that collects instances of the key's type in a {@link Set} that is * itself bound with the annotation (if any) of the key. * * @since 4.0 */ public static <T> Multibinder newSetBinder(Binder binder, Key key) { return newRealSetBinder(binder, key); } /** * Implementation of newSetBinder. */ static <T> RealMultibinder newRealSetBinder(Binder binder, Key key) { binder = binder.skipSources(RealMultibinder.class, Multibinder.class); RealMultibinder<T> result = new RealMultibinder(binder, key.getTypeLiteral(), key.ofType(setOf(key.getTypeLiteral()))); binder.install(result); return result; } /** * Returns a new multibinder that collects instances of {@code type} in a {@link Set} that is * itself bound with {@code annotationType}. */ public static <T> Multibinder newSetBinder(Binder binder, Class type, Class<? extends Annotation> annotationType) { return newSetBinder(binder, Key.get(type, annotationType)); } @SuppressWarnings("unchecked") // wrapping a T in a Set safely returns a Set<T> static <T> TypeLiteral> setOf(TypeLiteral elementType) { Type type = Types.setOf(elementType.getType()); return (TypeLiteral<Set) TypeLiteral.get(type); } @SuppressWarnings("unchecked") static <T> TypeLiteral>> collectionOfProvidersOf( TypeLiteral<T> elementType) { Type providerType = Types.providerOf(elementType.getType()); Type type = Types.collectionOf(providerType); return (TypeLiteral<Collection>) TypeLiteral.get(type); } @SuppressWarnings("unchecked") static <T> TypeLiteral>> collectionOfJavaxProvidersOf( TypeLiteral<T> elementType) { Type providerType = Types.newParameterizedType(javax.inject.Provider.class, elementType.getType()); Type type = Types.collectionOf(providerType); return (TypeLiteral<Collection>) TypeLiteral.get(type); } /** * Configures the bound set to silently discard duplicate elements. When multiple equal values are * bound, the one that gets included is arbitrary. When multiple modules contribute elements to * the set, this configuration option impacts all of them. * * @return this multibinder * @since 3.0 */ public abstract Multibinder<T> permitDuplicates(); /** * Returns a binding builder used to add a new element in the set. Each * bound element must have a distinct value. Bound providers will be * evaluated each time the set is injected. * * <p>It is an error to call this method without also calling one of the * {@code to} methods on the returned binding builder. * * <p>Scoping elements independently is supported. Use the {@code in} method * to specify a binding scope. */ public abstract LinkedBindingBuilder<T> addBinding(); /** * The actual multibinder plays several roles: * * <p>As a Multibinder, it acts as a factory for LinkedBindingBuilders for * each of the set's elements. Each binding is given an annotation that * identifies it as a part of this set. * * <p>As a Module, it installs the binding to the set itself. As a module, * this implements equals() and hashcode() in order to trick Guice into * executing its configure() method only once. That makes it so that * multiple multibinders can be created for the same target collection, but * only one is bound. Since the list of bindings is retrieved from the * injector itself (and not the multibinder), each multibinder has access to * all contributions from all multibinders. * * <p>As a Provider, this constructs the set instances. * * <p>We use a subclass to hide 'implements Module, Provider' from the public * API. */ static final class RealMultibinder<T> extends Multibinder implements Module, ProviderWithExtensionVisitor<Set, HasDependencies, MultibinderBinding<Set { private final TypeLiteral<T> elementType; private final String setName; private final Key<Set setKey; private final Key<Collection> collectionOfProvidersKey; private final Key<Collection> collectionOfJavaxProvidersKey; private final Key<Boolean> permitDuplicatesKey; /* the target injector's binder. non-null until initialization, null afterwards */ private Binder binder; /* a binding for each element in the set. null until initialization, non-null afterwards */ private ImmutableList<Binding bindings; private Set<Dependency dependencies; /** whether duplicates are allowed. Possibly configured by a different instance */ private boolean permitDuplicates; private RealMultibinder(Binder binder, TypeLiteral<T> elementType, Key> setKey) { this.binder = checkNotNull(binder, "binder"); this.elementType = checkNotNull(elementType, "elementType"); this.setKey = checkNotNull(setKey, "setKey"); this.collectionOfProvidersKey = setKey.ofType(collectionOfProvidersOf(elementType)); this.collectionOfJavaxProvidersKey = setKey.ofType(collectionOfJavaxProvidersOf(elementType)); this.setName = RealElement.nameOf(setKey); this.permitDuplicatesKey = Key.get(Boolean.class, named(toString() + " permits duplicates")); } public void configure(Binder binder) { checkConfiguration(!isInitialized(), "Multibinder was already initialized"); binder.bind(setKey).toProvider(this); binder.bind(collectionOfProvidersKey).toProvider( new RealMultibinderCollectionOfProvidersProvider()); // The collection this exposes is internally an ImmutableList, so it's OK to massage // the guice Provider to javax Provider in the value (since the guice Provider implements // javax Provider). @SuppressWarnings("unchecked") Key key = (Key) collectionOfProvidersKey; binder.bind(collectionOfJavaxProvidersKey).to(key); } @Override public Multibinder<T> permitDuplicates() { binder.install(new PermitDuplicatesModule(permitDuplicatesKey)); return this; } Key<T> getKeyForNewItem() { checkConfiguration(!isInitialized(), "Multibinder was already initialized"); return Key.get(elementType, new RealElement(setName, MULTIBINDER, "")); } @Override public LinkedBindingBuilder<T> addBinding() { return binder.bind(getKeyForNewItem()); } /** * Invoked by Guice at Injector-creation time to prepare providers for each * element in this set. At this time the set's size is known, but its * contents are only evaluated when get() is invoked. */ @Toolable @Inject void initialize(Injector injector) { List<Binding bindings = Lists.newArrayList(); Set<Indexer.IndexedBinding> index = Sets.newHashSet(); Indexer indexer = new Indexer(injector); List<Dependency dependencies = Lists.newArrayList(); for (Binding<?> entry : injector.findBindingsByType(elementType)) { if (keyMatches(entry.getKey())) { @SuppressWarnings("unchecked") // protected by findBindingsByType() Binding<T> binding = (Binding) entry; if (index.add(binding.acceptTargetVisitor(indexer))) { bindings.add(binding); dependencies.add(Dependency.get(binding.getKey())); } } } this.bindings = ImmutableList.copyOf(bindings); this.dependencies = ImmutableSet.copyOf(dependencies); this.permitDuplicates = permitsDuplicates(injector); this.binder = null; } // This is forked from com.google.common.collect.Maps.capacity private static int mapCapacity(int numBindings) { if (numBindings < 3) { return numBindings + 1; } else if (numBindings < MAX_POWER_OF_TWO) { return (int) (numBindings / 0.75F + 1.0F); } return Integer.MAX_VALUE; } boolean permitsDuplicates(Injector injector) { return injector.getBindings().containsKey(permitDuplicatesKey); } private boolean keyMatches(Key<?> key) { return key.getTypeLiteral().equals(elementType) && key.getAnnotation() instanceof Element && ((Element) key.getAnnotation()).setName().equals(setName) && ((Element) key.getAnnotation()).type() == MULTIBINDER; } private boolean isInitialized() { return binder == null; } public Set<T> get() { checkConfiguration(isInitialized(), "Multibinder is not initialized"); Map<T, Binding result = new LinkedHashMap>(mapCapacity(bindings.size())); for (Binding<T> binding : bindings) { final T newValue = binding.getProvider().get(); checkConfiguration(newValue != null, "Set injection failed due to null element bound at: %s", binding.getSource()); Binding<T> duplicateBinding = result.put(newValue, binding); if (!permitDuplicates && duplicateBinding != null) { throw newDuplicateValuesException(result, binding, newValue, duplicateBinding); } } return ImmutableSet.copyOf(result.keySet()); } @SuppressWarnings("unchecked") public <B, V> V acceptExtensionVisitor( BindingTargetVisitor<B, V> visitor, ProviderInstanceBinding<? extends B> binding) { if (visitor instanceof MultibindingsTargetVisitor) { return ((MultibindingsTargetVisitor<Set) visitor).visit(this); } else { return visitor.visit(binding); } } String getSetName() { return setName; } public TypeLiteral<?> getElementTypeLiteral() { return elementType; } public Key<Set getSetKey() { return setKey; } @SuppressWarnings("unchecked") public List<Binding getElements() { if (isInitialized()) { return (List<Binding) (List) bindings; // safe because bindings is immutable. } else { throw new UnsupportedOperationException("getElements() not supported for module bindings"); } } public boolean permitsDuplicates() { if (isInitialized()) { return permitDuplicates; } else { throw new UnsupportedOperationException( "permitsDuplicates() not supported for module bindings"); } } public boolean containsElement(com.google.inject.spi.Element element) { if (element instanceof Binding) { Binding<?> binding = (Binding) element; return keyMatches(binding.getKey()) || binding.getKey().equals(permitDuplicatesKey) || binding.getKey().equals(setKey) || binding.getKey().equals(collectionOfProvidersKey) || binding.getKey().equals(collectionOfJavaxProvidersKey); } else { return false; } } public Set<Dependency getDependencies() { if (!isInitialized()) { return ImmutableSet.<Dependencyof(Dependency.get(Key.get(Injector.class))); } else { return dependencies; } } @Override public boolean equals(Object o) { return o instanceof RealMultibinder && ((RealMultibinder<?>) o).setKey.equals(setKey); } @Override public int hashCode() { return setKey.hashCode(); } @Override public String toString() { return (setName.isEmpty() ? "" : setName + " ") + "Multibinder<" + elementType + ">"; } final class RealMultibinderCollectionOfProvidersProvider implements ProviderWithDependencies<Collection> { @Override public Collection<Provider get() { checkConfiguration(isInitialized(), "Multibinder is not initialized"); int size = bindings.size(); @SuppressWarnings("unchecked") // safe because we only put Provider<T> into it. Provider<T>[] providers = new Provider[size]; for (int i = 0; i < size; i++) { providers[i] = bindings.get(i).getProvider(); } return ImmutableList.copyOf(providers); } @Override public Set<Dependency getDependencies() { if (!isInitialized()) { return ImmutableSet.<Dependencyof(Dependency.get(Key.get(Injector.class))); } ImmutableSet.Builder<Dependency setBuilder = ImmutableSet.builder(); for (Dependency<?> dependency : dependencies) { Key key = dependency.getKey(); setBuilder.add( Dependency.get(key.ofType(Types.providerOf(key.getTypeLiteral().getType())))); } return setBuilder.build(); } Key getCollectionKey() { return RealMultibinder.this.collectionOfProvidersKey; } @Override public boolean equals(Object o) { return o instanceof Multibinder.RealMultibinder.RealMultibinderCollectionOfProvidersProvider && ((Multibinder.RealMultibinder.RealMultibinderCollectionOfProvidersProvider) o) .getCollectionKey().equals(getCollectionKey()); } @Override public int hashCode() { return getCollectionKey().hashCode(); } } } /** * We install the permit duplicates configuration as its own binding, all by itself. This way, * if only one of a multibinder's users remember to call permitDuplicates(), they're still * permitted. */ private static class PermitDuplicatesModule extends AbstractModule { private final Key<Boolean> key; PermitDuplicatesModule(Key<Boolean> key) { this.key = key; } @Override protected void configure() { bind(key).toInstance(true); } @Override public boolean equals(Object o) { return o instanceof PermitDuplicatesModule && ((PermitDuplicatesModule) o).key.equals(key); } @Override public int hashCode() { return getClass().hashCode() ^ key.hashCode(); } } static void checkConfiguration(boolean condition, String format, Object... args) { if (condition) { return; } throw new ConfigurationException(ImmutableSet.of(new Message(Errors.format(format, args)))); } private static <T> ConfigurationException newDuplicateValuesException( Map<T, Binding existingBindings, Binding<T> binding, final T newValue, Binding<T> duplicateBinding) { T oldValue = getOnlyElement(filter(existingBindings.keySet(), equalTo(newValue))); String oldString = oldValue.toString(); String newString = newValue.toString(); if (Objects.equal(oldString, newString)) { // When the value strings match, just show the source of the bindings return new ConfigurationException(ImmutableSet.of(new Message(Errors.format( "Set injection failed due to duplicated element \"%s\"" + "\n Bound at %s\n Bound at %s", newValue, duplicateBinding.getSource(), binding.getSource())))); } else { // When the value strings don't match, include them both as they may be useful for debugging return new ConfigurationException(ImmutableSet.of(new Message(Errors.format( "Set injection failed due to multiple elements comparing equal:" + "\n \"%s\"\n bound at %s" + "\n \"%s\"\n bound at %s", oldValue, duplicateBinding.getSource(), newValue, binding.getSource())))); } } static <T> T checkNotNull(T reference, String name) { if (reference != null) { return reference; } NullPointerException npe = new NullPointerException(name); throw new ConfigurationException(ImmutableSet.of( new Message(npe.toString(), npe))); } }

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