public List<String> getRack(List<ServerName> servers) {
    // just a note - switchMapping caches results (at least the implementation should unless the
    // resolution is really a lightweight process)
    List<String> serversAsString = new ArrayList<>(servers.size());
    for (ServerName server : servers) {
      serversAsString.add(server.getHostname());
    }
    List<String> racks = switchMapping.resolve(serversAsString);
    return racks;
  }
Same as {@link #getRack(ServerName)} except that a list is passed
@param servers list of servers we're requesting racks information for
@return list of racks for the given list of servers
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/RackManager.java