/**
    * Copyright By Grandsoft Company Limited.  
    * 2012-10-15 上午09:16:21
    */
   package gboat2.base.core.web;
   
   import gboat2.base.core.Activator;
   
   import org.osgi.framework.BundleContext;
  import org.osgi.util.tracker.ServiceTracker;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * 
   * 跟踪SystemButtonProvider的服务实现
   * @author tanxw
   * @since jdk1.6
   * @date 2012-10-15
   *  
   */
  
  public abstract class SystemButtonProviderTracker {
  	
  	@SuppressWarnings("rawtypes")
      private static ServiceTracker tracker = null;
  	
  	protected static Logger logger = LoggerFactory.getLogger(SystemButtonProviderTracker.class);
  	
  	private static byte[] lock = new byte[0];
  	
  	/**
  	 * 开启服务跟踪，使用者必须保证在调用服务获取方法{@see #getProviders()}之前调用
  	 * @param context bundle上下文
  	 */
  	@SuppressWarnings({ "rawtypes", "unchecked" })
      public static void open(BundleContext context) {
  		if (null != tracker) {//如果多次调用本方法打开跟踪器，在先关闭以前的，防止泄露
  			tracker.close();
  		}
  		tracker = new ServiceTracker(context, SystemButtonProvider.class.getName(), null);
  		tracker.open();
  	}
  	
  	/**
  	 *关闭跟踪器，建议的bundle关闭时，或者不在需要跟踪 WidgetService服务时，调用本方法，以便释放资源
  	 */
  	public static void close() {
  		if (null != tracker) {
  			tracker.close();
  			tracker = null;
  		}
  	}
  	
  	/**
  	 * 获取所有SystemButtonProvider的实现 ，由于服务时动态的，不要缓存本方法返回的结果
  	 * @return 所有SystemButtonProvider的实现
  	 */
  	public static SystemButtonProvider[] getProviders() {
  		synchronized (lock) {//打开跟踪器
  			if (null == tracker) {
  				open(Activator.LOCAL_BUNDLE.getBundleContext());
  			}
  		}
  		
  		Object[] objs = tracker.getServices();
  		if (null != objs) {
  			SystemButtonProvider[] services = new SystemButtonProvider[objs.length];
  			int i;
  			for (i = 0; i < objs.length; i++) {
  				services[i] = (SystemButtonProvider) objs[i];
  			}
  			return services;
  		}
  		
  		return null;
  	}
  }