@SneakyThrows
    public Service getService(final String serviceId) throws IOException {
        final List<Service> services = this.combineServices(this.serviceCache.get(true).get(serviceId));
        return CollectionUtils.isNotEmpty(services) ? services.get(0) : null;
    }
@return all services, key is service id, value is services with different layers.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/query/MetadataQueryService.java