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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 com.google.inject.Binder;
import com.google.inject.Key;
import com.google.inject.Provider;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
/**
* 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:
* <pre>
* Provider<PaymentService> paymentServiceProvider
* = getProvider(PaymentService.class);</pre>
*
* @author jessewilson@google.com (Jesse Wilson)
* @since 2.0
*/
public final class ProviderLookup<T> implements Element {
private final Object source;
private final Key<T> key;
private Provider<T> delegate;
public ProviderLookup(Object source, Key<T> key) {
this.source = checkNotNull(source, "source");
this.key = checkNotNull(key, "key");
}
public Object getSource() {
return source;
}
public Key<T> getKey() {
return key;
}
public <T> T acceptVisitor(ElementVisitor<T> visitor) {
return visitor.visit(this);
}
/**
* Sets the actual provider.
*
* @throws IllegalStateException if the delegate is already set
*/
public void initializeDelegate(Provider<T> delegate) {
checkState(this.delegate == null, "delegate already initialized");
this.delegate = checkNotNull(delegate, "delegate");
}
public void applyTo(Binder binder) {
initializeDelegate(binder.withSource(getSource()).getProvider(key));
}
/**
* 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<T> 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<T> getProvider() {
return new Provider<T>() {
public T get() {
checkState(delegate != null,
"This Provider cannot be used until the Injector has been created.");
return delegate.get();
}
@Override public String toString() {
return "Provider<" + key.getTypeLiteral() + ">";
}
};
}
}
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