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Java example source code file (ProviderInternalFactory.java)

This example Java source code file (ProviderInternalFactory.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

class, constructioncontext, dependency, errors, errorsexception, internalcontext, object, providerinternalfactory, provisioncallback, provisionlistenerstackcallback, suppresswarnings

The ProviderInternalFactory.java Java example source code

/**
 * Copyright (C) 2011 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.internal;

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

import com.google.inject.internal.ProvisionListenerStackCallback.ProvisionCallback;
import com.google.inject.spi.Dependency;

import javax.inject.Provider;

/**
 * Base class for InternalFactories that are used by Providers, to handle
 * circular dependencies.
 *
 * @author sameb@google.com (Sam Berlin)
 */
abstract class ProviderInternalFactory<T> implements InternalFactory {
  
  protected final Object source;
  
  ProviderInternalFactory(Object source) {
    this.source = checkNotNull(source, "source");
  }
  
  protected T circularGet(final Provider<? extends T> provider, final Errors errors,
      InternalContext context, final Dependency<?> dependency,
      ProvisionListenerStackCallback<T> provisionCallback)
      throws ErrorsException {    
    final ConstructionContext<T> constructionContext = context.getConstructionContext(this);

    // We have a circular reference between constructors. Return a proxy.
    if (constructionContext.isConstructing()) {
        Class<?> expectedType = dependency.getKey().getTypeLiteral().getRawType();
        // TODO: if we can't proxy this object, can we proxy the other object?
        @SuppressWarnings("unchecked")
        T proxyType = (T) constructionContext.createProxy(
            errors, context.getInjectorOptions(), expectedType);
        return proxyType;
    }

    // Optimization: Don't go through the callback stack if no one's listening.
    constructionContext.startConstruction();
    try {
      if (!provisionCallback.hasListeners()) {
        return provision(provider, errors, dependency, constructionContext);
      } else {
        return provisionCallback.provision(errors, context, new ProvisionCallback<T>() {
          public T call() throws ErrorsException {
            return provision(provider, errors, dependency, constructionContext);
          }
        });
      }
    } finally {
      constructionContext.removeCurrentReference();
      constructionContext.finishConstruction();
    }
  }

  /**
   * Provisions a new instance. Subclasses should override this to catch
   * exceptions & rethrow as ErrorsExceptions.
   */
  protected T provision(Provider<? extends T> provider, Errors errors, Dependency dependency,
      ConstructionContext<T> constructionContext) throws ErrorsException {
    T t = errors.checkForNull(provider.get(), source, dependency);
    constructionContext.setProxyDelegates(t);
    return t;
  }
}

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