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Java example source code file (ConstructionContext.java)

This example Java source code file (ConstructionContext.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

arraylist, class, classloader, constructioncontext, delegatinginvocationhandler, errorsexception, injectoroptions, list, object, reflection, util

The ConstructionContext.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,
 * See the License for the specific language governing permissions and
 * limitations under the License.

package com.google.inject.internal;

import com.google.inject.internal.InjectorImpl.InjectorOptions;

import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;

 * Context of a dependency construction. Used to manage circular references.
 * @author crazybob@google.com (Bob Lee)
final class ConstructionContext<T> {

  T currentReference;
  boolean constructing;

  List<DelegatingInvocationHandler invocationHandlers;

  public T getCurrentReference() {
    return currentReference;

  public void removeCurrentReference() {
    this.currentReference = null;

  public void setCurrentReference(T currentReference) {
    this.currentReference = currentReference;

  public boolean isConstructing() {
    return constructing;

  public void startConstruction() {
    this.constructing = true;

  public void finishConstruction() {
    this.constructing = false;
    invocationHandlers = null;

  public Object createProxy(Errors errors, InjectorOptions injectorOptions,
      Class<?> expectedType) throws ErrorsException {
    if (injectorOptions.disableCircularProxies) {
      throw errors.circularDependenciesDisabled(expectedType).toException();
    if (!expectedType.isInterface()) {
      throw errors.cannotProxyClass(expectedType).toException();

    if (invocationHandlers == null) {
      invocationHandlers = new ArrayList<DelegatingInvocationHandler();

    DelegatingInvocationHandler<T> invocationHandler = new DelegatingInvocationHandler();

    // TODO: if I create a proxy which implements all the interfaces of
    // the implementation type, I'll be able to get away with one proxy
    // instance (as opposed to one per caller).
    ClassLoader classLoader = BytecodeGen.getClassLoader(expectedType);
    return expectedType.cast(Proxy.newProxyInstance(classLoader,
        new Class[] { expectedType, CircularDependencyProxy.class }, invocationHandler));

  public void setProxyDelegates(T delegate) {
    if (invocationHandlers != null) {
      for (DelegatingInvocationHandler<T> handler : invocationHandlers) {
      // initialization of each handler can happen no more than once
      invocationHandlers = null;

Other Java examples (source code examples)

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