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.faces;
  
  import javax.faces.application.NavigationHandler;
  import javax.faces.context.FacesContext;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.shale.dialog.Constants;
  import org.apache.shale.dialog.DialogContext;
  import org.apache.shale.dialog.DialogContextManager;
  
  /***
   * <p><code>NavigationHandler</code> implementation that allows dialogs to
   * be created via a logical outcome that returns with a specified prefix.
   * This is not the only way to start a dialog instance (applications can also
   * do this programmatically), but it is convenient in many cases.</p>
   *
   * @since 1.0.4
   */
  public final class DialogNavigationHandler extends NavigationHandler {
  
  
      // ------------------------------------------------------------ Constructors
  
  
      /***
       * <p>Creates a new instance of DialogNavigationHandler that delegates
       * to the specified original handler.</p>
       *
       * @param original Original NavigationHandler
       */
      public DialogNavigationHandler(NavigationHandler original) {
          if (log.isInfoEnabled()) {
              log.info("Instantiating DialogNavigationHandler (wrapping instance '"
                       + original + "')");
          }
          this.original = original;
      }
  
  
      // ------------------------------------------------- DialogContext Variables
  
  
      /***
       * <p>The <code>Log</code> instance for this class.</p>
       */
      private Log log = LogFactory.getLog(DialogNavigationHandler.class);
  
  
      /***
       * <p>The original <code>NavigationHandler</code> we delegate to.</p>
       */
      private NavigationHandler original = null;
  
  
      // ----------------------------------------------- NavigationHandler Methods
  
  
      /***
       * <p>Handle a navigation request from the application.  The following
       * rules are applied:</p>
       * <ul>
       * <li>If this view is <strong>NOT</strong> currently executing
       *     a {@link DialogContext} instance:
       *     <ul>
       *     <li>If the logical outcome begins with the prefix identified
       *         by the prefix specified by context init parameter
       *         <code>Constants.DIALOG_PREFIX_PARAM</code> (with a default
       *         value of <code>Constants.DIALOG_PREFIX</code>), create and start
       *         a new {@link DialogContext} instance for a logical name
       *         based on the remainder of the logical outcome after the
       *         prefix.</li>
       *     <li>Otherwise, delegate control to the original navigation
       *         handler passed to our constructor.</li>
       *     </ul></li>
       * <li>If this view is currently executing a {@link DialogContext}
       *     instance, advance its progress based on the specified logical
       *     outcome.</li>
       * </ul>
       *
       * @param context FacesContext for the current request
       * @param fromAction Action that was invoked
      * @param outcome Logical outcome from the invoked action
      */
     public void handleNavigation(FacesContext context, String fromAction,
                                  String outcome) {
 
         if (log.isTraceEnabled()) {
             log.trace("handleNavigation(context='"
                       + context + "', fromAction='"
                       + fromAction + "', outcome='"
                       + outcome + "')");
         }
 
         DialogContext dcontext = (DialogContext)
           context.getExternalContext().getRequestMap().get(Constants.CONTEXT_BEAN);
         String prefix = prefix(context);
         if (dcontext == null) {
             if ((outcome != null) && outcome.startsWith(prefix)) {
                 // Create and start a new DialogContext instance
                 DialogContextManager manager = (DialogContextManager)
                   context.getApplication().getVariableResolver().
                   resolveVariable(context, Constants.MANAGER_BEAN);
                 dcontext =
                   manager.create(context, outcome.substring(prefix.length()));
                 dcontext.start(context);
                 if (log.isDebugEnabled()) {
                     log.debug("Starting dialog '"
                               + outcome.substring(prefix.length())
                               + "' for FacesContext instance '"
                               + context + "' with navigation to viewId '"
                               + context.getViewRoot().getViewId() + "'");
                 }
                 return;
             } else {
                 // No active dialog, so delegate to the original handler
                 original.handleNavigation(context, fromAction, outcome);
                 return;
             }
         } else {
             // Advance the currently active DialogContext instance
             dcontext.advance(context, outcome);
             if (log.isDebugEnabled()) {
                 log.debug("Advancing dialog '"
                           + dcontext.getName() + "' for FacesContext '"
                           + context + "' with navigation to viewId '"
                           + context.getViewRoot().getViewId() + "'");
             }
         }
 
     }
 
 
     // --------------------------------------------------------- Private Methods
 
 
     /***
      * <p>Cache the calculated value of the prefix that triggers starting
      * a dialog.</p>
      */
     private String prefix = null;
 
 
     /***
      * <p>Return the prefix string that indicates a logical outcome that
      * should trigger starting a dialog.  The default value can be overridden
      * by an appropriate context initialization parameter.</p>
      *
      * @param context <code>FacesContext</code> for the current request
      */
     private String prefix(FacesContext context) {
 
         if (prefix != null) {
             return prefix;
         }
         prefix = context.getExternalContext().
           getInitParameter(Constants.DIALOG_PREFIX_PARAM);
         if (prefix == null) {
             prefix = Constants.DIALOG_PREFIX;
         }
         return prefix;
 
     }
 
 
 }