code: public static Class getGeneric(final Class cls, final int index) {
  		Type[] generics = getGenerics(cls);
  		if ($.notEmpty(generics)) {
  			return (Class) generics[index];
  		}
  		return null;
  	}
docs: 获取指定位置的泛型
  
  @param cls
  @param index
  @return