package org.codehaus.plexus.component.manager;
   
   /*
    * Copyright 2001-2006 Codehaus Foundation.
    *
    * 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.
   */
  
  import org.codehaus.plexus.MutablePlexusContainer;
  import org.codehaus.plexus.component.factory.ComponentInstantiationException;
  import org.codehaus.plexus.component.repository.ComponentDescriptor;
  import org.codehaus.plexus.component.repository.exception.ComponentLifecycleException;
  import org.codehaus.plexus.lifecycle.LifecycleHandler;
  
  /**
   * This ensures a component is only used as a singleton, and is only shutdown when the container
   * shuts down.
   *
   * @author Jason van Zyl
   */
  public class SingletonComponentManager<T> extends AbstractComponentManager<T> {
      private T singleton;
  
      public SingletonComponentManager(
              MutablePlexusContainer container,
              LifecycleHandler lifecycleHandler,
              ComponentDescriptor<T> componentDescriptor,
              String role,
              String roleHint) {
          super(container, lifecycleHandler, componentDescriptor, role, roleHint);
      }
  
      public synchronized void release(Object component) throws ComponentLifecycleException {
          if (singleton == component) {
              dispose();
          }
      }
  
      public synchronized void dispose() throws ComponentLifecycleException {
          if (singleton != null) {
              endComponentLifecycle(singleton);
              singleton = null;
          }
      }
  
      public synchronized T getComponent() throws ComponentInstantiationException, ComponentLifecycleException {
          if (singleton == null) {
              singleton = createComponentInstance();
          }
  
          incrementConnectionCount();
  
          return singleton;
      }
  }