public List<ProviderInfo> currentProviders() {
        List<ProviderInfo> providerInfos = new ArrayList<>();
        Instance[] instances = currentData.getInstances();
        for (Instance instance : instances) {
            ProviderInfo providerInfo = ProviderHelper.toProviderInfo(convertInstanceToUrl(instance.getHost(), instance.getPort(), currentData.getMetadata()));
            providerInfos.add(providerInfo);
        }
        return providerInfos;
    }
observe the providers from polaris and notify the consumers

@author <a href=mailto:bner666@gmail.com>ZhangLibin</a>
registry/registry-polaris/src/main/java/com/alipay/sofa/rpc/registry/polaris/PolarisWatcher.java