public ConfigData<?> fetchConfig(final ConfigGroupEnum groupKey, final String namespaceId) {
        ConfigDataCache config = CACHE.get(HttpLongPollingDataChangedListener.buildCacheKey(namespaceId, groupKey.name()));
        switch (groupKey) {
            case APP_AUTH:
                return buildConfigData(config, AppAuthData.class);
            case PLUGIN:
                return buildConfigData(config, PluginData.class);
            case RULE:
                return buildConfigData(config, RuleData.class);
            case SELECTOR:
                return buildConfigData(config, SelectorData.class);
            case META_DATA:
                return buildConfigData(config, MetaData.class);
            case PROXY_SELECTOR:
                return buildConfigData(config, ProxySelectorData.class);
            case DISCOVER_UPSTREAM:
                return buildConfigData(config, DiscoverySyncData.class);
            default:
                throw new IllegalStateException("Unexpected groupKey: " + groupKey);
        }
    }
fetch configuration from cache.

@param groupKey    the group key
@param namespaceId the namespaceId
@return the configuration data
shenyu-admin/src/main/java/org/apache/shenyu/admin/listener/AbstractDataChangedListener.java