code: private static String selectSlave() {
  		//  无从库则路由到主库
  		if (slaves.isEmpty()) {
  			logger.debug("current no slave found ,default use [{}]!",master);
  			return master;
  		}
  		if (slaves.size() == 1)
  			return slaves.get(0);
  		
  		int selectIndex = (int) (counter.getAndIncrement() % slaves.size());
  		String slaveKey = slaves.get(selectIndex);
  		return slaveKey;
  	}
docs: 轮循分配slave节点
  
  @return