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/*
 * 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.spi;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.collect.ImmutableSet;
import com.google.inject.Binder;
import com.google.inject.Key;
import com.google.inject.Provider;
import com.google.inject.util.Types;
import java.util.Set;

/**
 * A lookup of the provider for a type. Lookups are created explicitly in a module using {@link
 * com.google.inject.Binder#getProvider(Class) getProvider()} statements:
 *
 * 
 *     Provider<PaymentService> paymentServiceProvider
 *         = getProvider(PaymentService.class);
* * @author [email protected] (Jesse Wilson) * @since 2.0 */ public final class ProviderLookup implements Element { private final Object source; private final Dependency dependency; private Provider delegate; public ProviderLookup(Object source, Key key) { this(source, Dependency.get(checkNotNull(key, "key"))); } /** @since 4.0 */ public ProviderLookup(Object source, Dependency dependency) { this.source = checkNotNull(source, "source"); this.dependency = checkNotNull(dependency, "dependency"); } @Override public Object getSource() { return source; } public Key getKey() { return dependency.getKey(); } /** @since 4.0 */ public Dependency getDependency() { return dependency; } @Override public T acceptVisitor(ElementVisitor visitor) { return visitor.visit(this); } /** * Sets the actual provider. * * @throws IllegalStateException if the delegate is already set */ public void initializeDelegate(Provider delegate) { checkState(this.delegate == null, "delegate already initialized"); this.delegate = checkNotNull(delegate, "delegate"); } @Override public void applyTo(Binder binder) { initializeDelegate(binder.withSource(getSource()).getProvider(dependency)); } /** * Returns the delegate provider, or {@code null} if it has not yet been initialized. The delegate * will be initialized when this element is processed, or otherwise used to create an injector. */ public Provider getDelegate() { return delegate; } /** * Returns the looked up provider. The result is not valid until this lookup has been initialized, * which usually happens when the injector is created. The provider will throw an {@code * IllegalStateException} if you try to use it beforehand. */ public Provider getProvider() { return new ProviderWithDependencies() { @Override public T get() { Provider local = delegate; if (local == null) { throw new IllegalStateException( "This Provider cannot be used until the Injector has been created."); } return local.get(); } @Override public Set> getDependencies() { // We depend on Provider, not T directly. This is an important distinction // for dependency analysis tools that short-circuit on providers. Key providerKey = getKey().ofType(Types.providerOf(getKey().getTypeLiteral().getType())); return ImmutableSet.>of(Dependency.get(providerKey)); } @Override public String toString() { return "Provider<" + getKey().getTypeLiteral() + ">"; } }; } }




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