ASP.NET Google Site Map Provider

/*
 * 
 * iFinity Smart Business Solutions - http://www.ifinity.com.au
 * Copyright (c) 2006
 
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated 
 * documentation files (the "Software"), the rights to use, copy, modify, merge, publish, distribute, sublicense
 * copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the 
 * following conditions:

 * 1. The above copyright notice and this permission notice shall be included in all copies or substantial portions 
 *    of the Software.  
 * 2. The software may not be claimed as the original work of anyone other than the author and may not be sold as 
 *    a stand alone product

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED 
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF 
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
 * DEALINGS IN THE SOFTWARE.
 * 
 */

using System;
using System.Collections.Generic;
using System.Text;

using System.Web.Configuration;
using System.Configuration.Provider;

namespace iFinity.Providers.GoogleSiteMap
{
    public class GoogleSiteMapService
    {
        private static GoogleSiteMapProvider _provider = null;
        private static GoogleSiteMapProviderCollection _providers = null;
        private static object _lock = new object();

        public static string GetGoogleSiteMap(string siteURL)
        {
            //ensure providers are loaded
            LoadSiteMapProviders();
            //delegate to the default provider
            return _provider.GetGoogleSiteMap(siteURL);
        }
        private static void LoadSiteMapProviders()
        {
            if (_provider == null)
            {
                lock (_lock)
                {
                    //double check provider still null
                    if (_provider == null)
                    {
                        //get reference to GoogleSiteMaps section
                        GoogleSiteMapSection section = (GoogleSiteMapSection)WebConfigurationManager.GetSection("googlesitemaps");

                        //load the registered providers and point _provider to default provider
                        _providers = new GoogleSiteMapProviderCollection();
                        ProvidersHelper.InstantiateProviders(section.Providers, _providers, typeof(GoogleSiteMapProvider));
                        _provider = _providers[section.DefaultProvider];

                        if (_provider == null)
                        {
                            throw new ProviderException("Unable to load default GoogleSiteMapProvider");
                        }
                    }
                }
            }

        }
    }
}