/**
* 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 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.internal.ImmutableList;
import com.google.inject.internal.ImmutableSet;
import com.google.inject.internal.Lists;
import com.google.inject.spi.Dependency;
import com.google.inject.spi.HasDependencies;
import com.google.inject.spi.Message;
import com.google.inject.util.Types;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
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><code>
* 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></pre>
*
* <p>With this binding, a {@link Set}{@code <Snack>} can now be injected:
* <pre><code>
* class SnackMachine {
* {@literal @}Inject
* public SnackMachine(Set<Snack> snacks) { ... }
* }</code></pre>
*
* <p>Create multibindings from different modules is supported. For example, it
* is okay to have both {@code CandyModule} and {@code ChipsModule} to both
* 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>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><strong>Elements must be distinct.</strong> If multiple bound elements
* have the same value, set injection will fail.
*
* <p><strong>Elements must be non-null.</strong> 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<T> newSetBinder(Binder binder, TypeLiteral<T> type) {
binder = binder.skipSources(RealMultibinder.class, Multibinder.class);
RealMultibinder<T> result = new RealMultibinder<T>(binder, type, "",
Key.get(Multibinder.<T>setOf(type)));
binder.install(result);
return result;
}
/**
* 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<T> newSetBinder(Binder binder, Class<T> type) {
return newSetBinder(binder, TypeLiteral.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<T> newSetBinder(
Binder binder, TypeLiteral<T> type, Annotation annotation) {
binder = binder.skipSources(RealMultibinder.class, Multibinder.class);
RealMultibinder<T> result = new RealMultibinder<T>(binder, type, annotation.toString(),
Key.get(Multibinder.<T>setOf(type), annotation));
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 annotation}.
*/
public static <T> Multibinder<T> newSetBinder(
Binder binder, Class<T> type, Annotation annotation) {
return newSetBinder(binder, TypeLiteral.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<T> newSetBinder(Binder binder, TypeLiteral<T> type,
Class<? extends Annotation> annotationType) {
binder = binder.skipSources(RealMultibinder.class, Multibinder.class);
RealMultibinder<T> result = new RealMultibinder<T>(binder, type, "@" + annotationType.getName(),
Key.get(Multibinder.<T>setOf(type), annotationType));
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<T> newSetBinder(Binder binder, Class<T> type,
Class<? extends Annotation> annotationType) {
return newSetBinder(binder, TypeLiteral.get(type), annotationType);
}
@SuppressWarnings("unchecked") // wrapping a T in a Set safely returns a Set<T>
private static <T> TypeLiteral<Set<T>> setOf(TypeLiteral<T> elementType) {
Type type = Types.setOf(elementType.getType());
return (TypeLiteral<Set<T>>) TypeLiteral.get(type);
}
/**
* 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<T>
implements Module, Provider<Set<T>>, HasDependencies {
private final TypeLiteral<T> elementType;
private final String setName;
private final Key<Set<T>> setKey;
/* the target injector's binder. non-null until initialization, null afterwards */
private Binder binder;
/* a provider for each element in the set. null until initialization, non-null afterwards */
private List<Provider<T>> providers;
private Set<Dependency<?>> dependencies;
private RealMultibinder(Binder binder, TypeLiteral<T> elementType,
String setName, Key<Set<T>> setKey) {
this.binder = checkNotNull(binder, "binder");
this.elementType = checkNotNull(elementType, "elementType");
this.setName = checkNotNull(setName, "setName");
this.setKey = checkNotNull(setKey, "setKey");
}
@SuppressWarnings("unchecked")
public void configure(Binder binder) {
checkConfiguration(!isInitialized(), "Multibinder was already initialized");
binder.bind(setKey).toProvider(this);
}
@Override public LinkedBindingBuilder<T> addBinding() {
checkConfiguration(!isInitialized(), "Multibinder was already initialized");
return binder.bind(Key.get(elementType, new RealElement(setName)));
}
/**
* 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.
*/
@Inject void initialize(Injector injector) {
providers = Lists.newArrayList();
List<Dependency<?>> dependencies = Lists.newArrayList();
for (Binding<?> entry : injector.findBindingsByType(elementType)) {
if (keyMatches(entry.getKey())) {
@SuppressWarnings("unchecked") // protected by findBindingsByType()
Binding<T> binding = (Binding<T>) entry;
providers.add(binding.getProvider());
dependencies.add(Dependency.get(binding.getKey()));
}
}
this.dependencies = ImmutableSet.copyOf(dependencies);
this.binder = null;
}
private boolean keyMatches(Key<?> key) {
return key.getTypeLiteral().equals(elementType)
&& key.getAnnotation() instanceof Element
&& ((Element) key.getAnnotation()).setName().equals(setName);
}
private boolean isInitialized() {
return binder == null;
}
public Set<T> get() {
checkConfiguration(isInitialized(), "Multibinder is not initialized");
Set<T> result = new LinkedHashSet<T>();
for (Provider<T> provider : providers) {
final T newValue = provider.get();
checkConfiguration(newValue != null, "Set injection failed due to null element");
checkConfiguration(result.add(newValue),
"Set injection failed due to duplicated element \"%s\"", newValue);
}
return Collections.unmodifiableSet(result);
}
String getSetName() {
return setName;
}
Key<Set<T>> getSetKey() {
return setKey;
}
public Set<Dependency<?>> getDependencies() {
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 new StringBuilder()
.append(setName)
.append(setName.length() > 0 ? " " : "")
.append("Multibinder<")
.append(elementType)
.append(">")
.toString();
}
}
static void checkConfiguration(boolean condition, String format, Object... args) {
if (condition) {
return;
}
throw new ConfigurationException(ImmutableSet.of(new Message(Errors.format(format, args))));
}
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(ImmutableList.of(), npe.toString(), npe)));
}
}