code: public static Class<?> checkClassExist(String className) {
  		Class<?> result = classExistCache.get(className);
  		if (result != null) {
  			if (ClassOrMethodNotExist.class.equals(result))
  				return null;
  			else
  				return result;
  		}
  		try {
  			result = Class.forName(className);
  			if (result != null)
  				classExistCache.put(className, result);
  			else
  				classExistCache.put(className, ClassOrMethodNotExist.class);
  			return result;
  		} catch (Exception e) {
  			DialectException.eatException(e);
  			classExistCache.put(className, ClassOrMethodNotExist.class);
  			return null;
  		}
  	}
docs: * Check class if exist, if exit return it, otherwise return null