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Java example source code file (ProviderLookup.java)

This example Java source code file (ProviderLookup.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

dependency, element, injector, key, object, override, provider, providerlookup, providerwithdependencies, set, string, this, util

The ProviderLookup.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.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:
 * <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 Dependency<T> dependency;
  private Provider<T> delegate;

  public ProviderLookup(Object source, Key<T> key) {
    this(source, Dependency.get(checkNotNull(key, "key")));
  }

  /** @since 4.0 */
  public ProviderLookup(Object source, Dependency<T> dependency) {
    this.source = checkNotNull(source, "source");
    this.dependency = checkNotNull(dependency, "dependency");
  }

  public Object getSource() {
    return source;
  }

  public Key<T> getKey() {
    return dependency.getKey();
  }

  /** @since 4.0 */
  public Dependency<T> getDependency() {
    return dependency;
  }

  public <T> T acceptVisitor(ElementVisitor 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(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<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 ProviderWithDependencies<T>() {
      public T get() {
        checkState(delegate != null,
            "This Provider cannot be used until the Injector has been created.");
        return delegate.get();
      }

      public Set<Dependency getDependencies() {
        // We depend on Provider<T>, 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.<Dependencyof(Dependency.get(providerKey));
      }

      @Override public String toString() {
        return "Provider<" + getKey().getTypeLiteral() + ">";
      }
    };
  }
}

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