code: public boolean checkAndScan() {
  		String changeLogs=null;
  		try {
  			synchronized (lock) {
  				checkFileChange();
  			}
  			if(changes.isEmpty())
  			{
  				return false;
  			}
  			for(;;)
  			{
  				String log=changes.poll();
  				if(log==null)
  				{
  					break;
  				}
  				if(changeLogs==null)
  				{
  					changeLogs="";
  				}
  				changeLogs+=log+"\n";
  			}
  		} catch (Throwable e) {
  			log.error(e.getMessage(),e);
  		}
  		if(changeLogs!=null)
  		{
  			log.debug("startScanClassSources from events:\n"+changeLogs);
  			scanClassSources();
  			return true;
  		}
  		return false;
  	}
docs: 检查是否发生变化,如果发生变化则更新