public class ApplicationDispatchHandler extends CommandHandlerBase {
    //CommandHandlerBase is the base class of the commands we want to execute

    //default handlers are those provided by the NAC framework
    private final static Map<AppCommandType, Class<? extends CommandHandlerBase>> defaultHandlers =
            new HashMap<AppCommandType, Class<? extends CommandHandlerBase>>();

    //override handlers store custom behavior to override the behavior supplied by the NAC framework
    //this allows customers to specify their own behavior for any particular app command type, while
    //maintaining core behavior for all other app command types
    private final static Map<AppCommandType, Class<? extends CommandHandlerBase>> overrideHandlers =
            new HashMap<AppCommandType, Class<? extends CommandHandlerBase>>();

    static {
        registerDefaultHandler(AppCommandType.ALARM, AlarmAppHandler.class);
        registerDefaultHandler(AppCommandType.CALENDAR, CalendarAppHandler.class);
        registerDefaultHandler(AppCommandType.CALLING, VoiceDialHandler.class);
        //...
    }

    private static void registerDefaultHandler(AppCommandType key, Class<? extends CommandHandlerBase> handler) {
        defaultHandlers.put(key, handler);
    }

    public static void registerHandler(AppCommandType key, Class<? extends CommandHandlerBase> handler) {
        overrideHandlers.put(key, handler);
    }

    public static void unregisterHandler(AppCommandType key) {
        overrideHandlers.remove(key);
    }

    public static void unregisterAll() {
        overrideHandlers.clear();
    }

    @Override
    public boolean execute(String appTypeString) {
        //...
        AppCommandType appType = getAppType(appTypeString);
        if (appType == null) {
            log.error("No AppType found for action: " + appTypeString);
            return false;
        }

        Class<? extends CommandHandlerBase> handlerClass = getHandler(appType);
        CommandHandlerBase handler = null;
        if (handlerClass != null) {

            try {
                handler = handlerClass.getDeclaredConstructor(ICommandHandlerListener.class).newInstance(getListener());
            } catch (Exception e) {
                e.printStackTrace();
                return false;
            }
        }
        // operate on the handler
        //...
   }

    private AppCommandType getAppType(String appTypeString) {
        AppCommandType appType = null;
        try {
            appType = new AppCommandType(appTypeString);
        } catch (IllegalArgumentException e) {
            log.error("App name '" + action.getApp() + "' is not supported");
            return null;
        }
        return appType;
    }


    private static Class<? extends CommandHandlerBase> getHandler(AppCommandType appType) {
        //CommandHandlerBase not shown here
        Class<? extends CommandHandlerBase> handlerClass = null;
        handlerClass = overrideHandlers.get(appType);
        if (handlerClass == null) {
            handlerClass = defaultHandlers.get(appType);
        }
        return handlerClass;
    }
}