@Override
    public void set(ConfigType configType, ConfigItem configItem, Object value) {
        validate(configType, configItem, value);
        Map<ConfigItem, Object> items = userConfigs.get(configType);
        if (null == items) {
            items = new HashMap<ConfigItem, Object>();
            userConfigs.put(configType, items);
        }
        Object prev = items.put(configItem, value);
        if (null != prev) {
            logger.warn("the value of ConfigType {}, ConfigItem {} changed from {} to {}",
                configType, configItem, prev.toString(), value.toString());
        }
    }
use a hash map to store the user configs with different config types and config items.
src/main/java/com/alipay/remoting/config/configs/DefaultConfigContainer.java