2009/05/20 - Apache Shale has been retired.

   /*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to you 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 org.apache.shale.dialog.base;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.shale.dialog.DialogContext;
  import org.apache.shale.dialog.DialogContextListener;
  
  /***
   * <p>Convenience abstract {@link DialogContext} implementation.
   * Provides listener registration and convenience event firing methods.
   * Subclasses are expected to be serializable.</p>
   *
   * @since 1.0.4
   */
  public abstract class AbstractDialogContext implements DialogContext {
  
  
      // -------------------------------------------------------------- Properties
  
  
      /***
       * The list of all registered {@link DialogContextListener}s for this
       * {@link DialogContext}.
       */
      private List listeners = new ArrayList();
  
  
      /***
       * <p>The <code>Log</code> instance for this class.</p>
       */
      private transient Log log;
  
  
      // ---------------------------------------------------- Listener Bookkeeping
  
  
      /***
       * Register given {@link DialogContextListener} for this {@link DialogContext}.
       * Listener cannot be <code>null</code>.
       *
       * @param listener The {@link DialogContextListener} instance.
       */
      public void addDialogContextListener(DialogContextListener listener) {
  
          if (listener == null) {
              throw new IllegalArgumentException("Cannot register null DialogContextListener");
          }
  
          synchronized (listeners) {
              if (listeners.contains(listener)) {
                  throw new IllegalArgumentException("DialogContextListener already registered");
              }
              listener.setDialogContext(this); // attach self reference
              listeners.add(listener);
          }
      }
  
  
      /***
       * Return the set of currently registered {@link DialogContextListener}s.
       */
      public DialogContextListener[] getDialogContextListeners() {
  
          synchronized (listeners) {
              return (DialogContextListener[])
                listeners.toArray(new DialogContextListener[listeners.size()]);
          }
  
      }
  
  
      /***
       * Remove this previously registered {@link DialogContextListener} for this
       * {@link DialogContext}. The listener will no longer receive any
       * associated callbacks.
       *
       * @param listener The {@link DialogContextListener} instance.
       */
      public void removeDialogContextListener(DialogContextListener listener) {
 
         if (listener == null) {
             throw new IllegalArgumentException("Cannot remove null DialogContextListener");
         }
 
         boolean removed;
         synchronized (listeners) {
             removed = listeners.remove(listener);
         }
         if (removed) {
             listener.setDialogContext(null); // detach self reference
         }
 
     }
 
 
     // -------------------- Utilities for firing DialogContextListener callbacks
 
 
     /***
      * Inform all registered {@link DialogContextListener}s that the dialog
      * instance has begun execution.
      *
      */
     protected void fireOnStart() {
 
         DialogContextListener[] listeners = getDialogContextListeners();
         for (int i = 0; i < listeners.length; i++) {
             listeners[i].onStart();
         }
 
     }
 
 
     /***
      * Inform all registered {@link DialogContextListener}s that the dialog
      * instance has finished execution normally.
      *
      */
     protected void fireOnStop() {
 
         DialogContextListener[] listeners = getDialogContextListeners();
         for (int i = 0; i < listeners.length; i++) {
             listeners[i].onStop();
         }
 
     }
 
 
     /***
      * Inform all registered {@link DialogContextListener}s that the dialog
      * instance has encountered an unexpected error condition. The exception
      * is first logged for archival.
      *
      * @param exception A potentially implementation specific exception
      *                  during the execution of this dialog instance
      */
     protected void fireOnException(Exception exception) {
 
         log().error(exception.getMessage(), exception);
 
         DialogContextListener[] listeners = getDialogContextListeners();
         for (int i = 0; i < listeners.length; i++) {
             listeners[i].onException(exception);
         }
 
     }
 
 
     /***
      * Inform all registered {@link DialogContextListener}s that the dialog instance
      * execution has entered a particular state.
      *
      * @param stateId Implementation specific identifier of the state
      *                that has been entered
      */
     protected void fireOnEntry(String stateId) {
 
         DialogContextListener[] listeners = getDialogContextListeners();
         for (int i = 0; i < listeners.length; i++) {
             listeners[i].onEntry(stateId);
         }
 
     }
 
 
     /***
      * Inform all registered {@link DialogContextListener}s that the dialog instance
      * execution has exited a particular state.
      *
      * @param stateId Implementation specific identifier of the state
      *                that has been exited
      */
     protected void fireOnExit(String stateId) {
 
         DialogContextListener[] listeners = getDialogContextListeners();
         for (int i = 0; i < listeners.length; i++) {
             listeners[i].onExit(stateId);
         }
 
     }
 
 
     /***
      * Inform all registered {@link DialogContextListener}s that the dialog instance
      * execution has followed a particular transition.
      *
      * @param fromStateId Implementation specific identifier of the source
      *                    state for the transition that has been followed
      * @param toStateId Implementation specific identifier of the target
      *                  state for the transition that has been followed
      */
     protected void fireOnTransition(String fromStateId, String toStateId) {
 
         DialogContextListener[] listeners = getDialogContextListeners();
         for (int i = 0; i < listeners.length; i++) {
             listeners[i].onTransition(fromStateId, toStateId);
         }
 
     }
 
 
     /***
      * <p>Return the <code>Log</code> instance for this class.</p>
      */
     private Log log() {
 
         if (log == null) {
             log = LogFactory.getLog(AbstractDialogContext.class);
         }
         return log;
 
     }
 
 }