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Java 1.6+ Library with tons of utility classes required in all projects
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/**
 * Copyright (C) 2014-2016 Philip Helger (www.helger.com)
 * philip[at]helger[dot]com
 *
 * 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.helger.commons.scope.singleton;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import com.helger.commons.annotation.ReturnsMutableCopy;
import com.helger.commons.collection.ext.ICommonsList;
import com.helger.commons.scope.IApplicationScope;
import com.helger.commons.scope.mgr.ScopeManager;

/**
 * This is the base class for singleton objects that reside in the application
 * scope. This is the same for web scopes and non-web scopes, as application
 * scopes are managed in the global scope which is also identical for web scopes
 * and non-web scopes.
 *
 * @see com.helger.commons.scope.mgr.EScope#APPLICATION
 * @author Philip Helger
 */
public abstract class AbstractApplicationSingleton extends AbstractSingleton
{
  protected AbstractApplicationSingleton ()
  {}

  /**
   * @param bCreateIfNotExisting
   *        true to create a new scope, if none is present yet,
   *        false to return null if either no global
   *        scope or no application scope is present.
   * @return The scope to be used for this type of singleton.
   */
  @Nullable
  private static IApplicationScope _getStaticScope (final boolean bCreateIfNotExisting)
  {
    return ScopeManager.getApplicationScope (bCreateIfNotExisting);
  }

  /**
   * Get the singleton object in the current application scope, using the passed
   * class. If the singleton is not yet instantiated, a new instance is created.
   *
   * @param 
   *        The type to be returned
   * @param aClass
   *        The class to be used. May not be null. The class must
   *        be public as needs to have a public no-argument constructor.
   * @return The singleton object and never null.
   */
  @Nonnull
  public static final  T getApplicationSingleton (@Nonnull final Class  aClass)
  {
    return getSingleton (_getStaticScope (true), aClass);
  }

  /**
   * Get the singleton object if it is already instantiated inside the current
   * application scope or null if it is not instantiated.
   *
   * @param 
   *        The type to be returned
   * @param aClass
   *        The class to be checked. May not be null.
   * @return The singleton for the specified class is already instantiated,
   *         null otherwise.
   */
  @Nullable
  public static final  T getApplicationSingletonIfInstantiated (@Nonnull final Class  aClass)
  {
    return getSingletonIfInstantiated (_getStaticScope (false), aClass);
  }

  /**
   * Check if a singleton is already instantiated inside the current application
   * scope
   *
   * @param aClass
   *        The class to be checked. May not be null.
   * @return true if the singleton for the specified class is
   *         already instantiated, false otherwise.
   */
  public static final boolean isApplicationSingletonInstantiated (@Nonnull final Class  aClass)
  {
    return isSingletonInstantiated (_getStaticScope (false), aClass);
  }

  /**
   * Get all instantiated singleton objects registered in the current
   * application scope.
   *
   * @return A non-null list with all instances of this class in
   *         the current application scope.
   */
  @Nonnull
  @ReturnsMutableCopy
  public static final ICommonsList  getAllApplicationSingletons ()
  {
    return getAllSingletons (_getStaticScope (false), AbstractApplicationSingleton.class);
  }
}