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Java example source code file (ConstructorInjector.java)

This example Java source code file (ConstructorInjector.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, constructionproxy, constructorinjector, errorsexception, immutableset, injectoroptions, internalcontext, invocationtargetexception, membersinjectorimpl, object, reflection, singleparameterinjector, throwable, util

The ConstructorInjector.java Java example source code

/**
 * Copyright (C) 2006 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 com.google.common.collect.ImmutableSet;
import com.google.inject.internal.InjectorImpl.InjectorOptions;
import com.google.inject.internal.ProvisionListenerStackCallback.ProvisionCallback;
import com.google.inject.spi.InjectionPoint;

import java.lang.reflect.InvocationTargetException;
import java.util.Set;

/**
 * Creates instances using an injectable constructor. After construction, all injectable fields and
 * methods are injected.
 *
 * @author crazybob@google.com (Bob Lee)
 */
final class ConstructorInjector<T> {

  private final ImmutableSet<InjectionPoint> injectableMembers;
  private final SingleParameterInjector<?>[] parameterInjectors;
  private final ConstructionProxy<T> constructionProxy;
  private final MembersInjectorImpl<T> membersInjector;

  ConstructorInjector(Set<InjectionPoint> injectableMembers,
      ConstructionProxy<T> constructionProxy,
      SingleParameterInjector<?>[] parameterInjectors,
      MembersInjectorImpl<T> membersInjector) {
    this.injectableMembers = ImmutableSet.copyOf(injectableMembers);
    this.constructionProxy = constructionProxy;
    this.parameterInjectors = parameterInjectors;
    this.membersInjector = membersInjector;
  }

  public ImmutableSet<InjectionPoint> getInjectableMembers() {
    return injectableMembers;
  }

  ConstructionProxy<T> getConstructionProxy() {
    return constructionProxy;
  }

  /**
   * Construct an instance. Returns {@code Object} instead of {@code T} because
   * it may return a proxy.
   */
  Object construct(final Errors errors, final InternalContext context,
      Class<?> expectedType,
      ProvisionListenerStackCallback<T> provisionCallback)
      throws ErrorsException {
    final ConstructionContext<T> constructionContext = context.getConstructionContext(this);
    InjectorOptions options = context.getInjectorOptions();

    // We have a circular reference between constructors. Return a proxy.
    if (constructionContext.isConstructing()) {
      // TODO (crazybob): if we can't proxy this object, can we proxy the other object?
      return constructionContext.createProxy(errors, options, expectedType);
    }

    // If we're re-entering this factory while injecting fields or methods,
    // return the same instance. This prevents infinite loops.
    T t = constructionContext.getCurrentReference();
    if (t != null) {
      if (options.disableCircularProxies) {
        throw errors.circularDependenciesDisabled(expectedType).toException();
      } else {
        return t;
      }
    }

    constructionContext.startConstruction();
    try {
      // Optimization: Don't go through the callback stack if we have no listeners.
      if (!provisionCallback.hasListeners()) {
        return provision(errors, context, constructionContext);
      } else {
        return provisionCallback.provision(errors, context, new ProvisionCallback<T>() {
          @Override
          public T call() throws ErrorsException {
            return provision(errors, context, constructionContext);
          }
        });
      }
    } finally {
      constructionContext.finishConstruction();
    }
  }

  /** Provisions a new T. */
  private T provision(Errors errors, InternalContext context,
      ConstructionContext<T> constructionContext) throws ErrorsException {
    try {
      T t;
      try {
        Object[] parameters = SingleParameterInjector.getAll(errors, context, parameterInjectors);
        t = constructionProxy.newInstance(parameters);
        constructionContext.setProxyDelegates(t);
      } finally {
        constructionContext.finishConstruction();
      }

      // Store reference. If an injector re-enters this factory, they'll get the same reference.
      constructionContext.setCurrentReference(t);

      membersInjector.injectMembers(t, errors, context, false);
      membersInjector.notifyListeners(t, errors);

      return t;
    } catch (InvocationTargetException userException) {
      Throwable cause = userException.getCause() != null
          ? userException.getCause()
          : userException;
      throw errors.withSource(constructionProxy.getInjectionPoint())
          .errorInjectingConstructor(cause).toException();
    } finally {
      constructionContext.removeCurrentReference();
    }
  }
}

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