code: public static Cluster getCluster(ZkClient zkClient) {
          Cluster cluster = new Cluster();
          List<String> nodes = getChildrenParentMayNotExist(zkClient, BrokerIdsPath);
          for (String node : nodes) {
              final String brokerInfoString = readData(zkClient, BrokerIdsPath + "/" + node);
              cluster.add(Broker.createBroker(Integer.valueOf(node), brokerInfoString));
          }
          return cluster;
      }
docs: read all brokers in the zookeeper
  
  @param zkClient zookeeper client
  @return all brokers