code: public static CoordinatorRegistryCenter createCoordinatorRegistryCenter(final String connectString, final String namespace, final Optional<String> digest) {
          Hasher hasher = Hashing.md5().newHasher().putString(connectString, Charsets.UTF_8).putString(namespace, Charsets.UTF_8);
          if (digest.isPresent()) {
              hasher.putString(digest.get(), Charsets.UTF_8);
          }
          HashCode hashCode = hasher.hash();
          CoordinatorRegistryCenter result = REG_CENTER_REGISTRY.get(hashCode);
          if (null != result) {
              return result;
          }
          MergeConfig zkConfig = new MergeConfig();
          zkConfig.addExt(ConfigEnum.address.getName(), connectString);
          zkConfig.addExt(ConfigEnum.namespace.getName(), namespace);
          if (digest.isPresent()) {
              zkConfig.addExt(ConfigEnum.digest.getName(), digest.get());
          }
          result = new ZookeeperRegistryCenter(zkConfig);
          result.init();
          REG_CENTER_REGISTRY.put(hashCode, result);
          return result;
      }
docs: 创建注册中心.
  
  @param connectString 注册中心连接字符串
  @param namespace 注册中心命名空间
  @param digest 注册中心凭证
  @return 注册中心对象