view java/src/uk/ac/qmul/eecs/ccmi/utils/PreferencesService.java @ 0:9418ab7b7f3f

Initial import

/*  
 CCmI Editor - A Collaborative Cross-Modal Diagram Editing Tool
	  
 Copyright (C) 2002 Cay S. Horstmann (http://horstmann.com)
 Copyright (C) 2011  Queen Mary University of London (http://ccmi.eecs.qmul.ac.uk/)

 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package uk.ac.qmul.eecs.ccmi.utils;

import java.util.prefs.Preferences;

/**
 * A service for storing and loading user preferences.
 */
public abstract class PreferencesService
{
   /**
    * Gets an instance of the service, suitable for the package of the given class.
    * @return an instance of the service
    */
   public static PreferencesService getInstance(){
      if (service != null) return service;
      try{
         service = new DefaultPreferencesService();
         return service;
      }
      catch (SecurityException exception){
         // that happens when we run under Web Start         
      }
      
      return new NullPreferencesService();
   }
   
   /**
    * Gets a previously stored string from the service.
    * @param key the key of the string
    * @param defval the value to return if no matching value was found
    * @return the value stored with the given key, or defval if none was found 
    */
   public abstract String get(String key, String defval);
   /**
    * Saves a key/value pair for later retrieval.
    * @param key the key of the string to be stored
    * @param value the value to to be stored
    */
   public abstract void put(String key, String value);
   
   private static PreferencesService service;
}

/**
 * The default preferences service that uses the java.util.prefs API. 
 */
class DefaultPreferencesService extends PreferencesService{   
   /**
    * Gets an instance of the service, suitable for the package of the given class.
    * @param appClass the main application class (only the package name is used as the path to  
    * app-specific preferences storage)
    * @return an instance of the service
    */
   public DefaultPreferencesService()
   {
      prefs = Preferences.userNodeForPackage(this.getClass());   
   }
   
   public String get(String key, String defval) { return prefs.get(key, defval); }
   public void put(String key, String defval) { prefs.put(key, defval); }

   private Preferences prefs;
}

/**
 * The null preferences service that is returned when we are an applet. 
 */
class NullPreferencesService extends PreferencesService {   
   public String get(String key, String defval) { return defval; }
   public void put(String key, String defval) { }
}