code: public static ClientTransport getReverseClientTransport(String channelKey) {
          return REVERSE_CLIENT_TRANSPORT_MAP != null ?
              REVERSE_CLIENT_TRANSPORT_MAP.get(channelKey) : null;
      }
docs: Find reverse client transport by channel key
  
  @param channelKey channel key
  @return client transport
  @see ClientTransportFactory#getReverseClientTransport
  @see NetUtils#channelToString