code: public Dict filter(String... keys) {
  		final Dict result = new Dict(keys.length, 1);
  
  		for (String key : keys) {
  			if (this.containsKey(key)) {
  				result.put(key, this.get(key));
  			}
  		}
  		return result;
  	}
docs: 过滤Map保留指定键值对，如果键不存在跳过
  
  @param keys 键列表
  @return Dict 结果
  @since 4.0.10