@Override
    public Upstream select(final List<Upstream> upstreamList, final String ip) {
        if (CollectionUtils.isEmpty(upstreamList)) {
            return null;
        }
        if (upstreamList.size() == 1) {
            return upstreamList.get(0);
        }
        return doSelect(upstreamList, ip);
    }
Do select upstream.

@param upstreamList the upstream list
@param ip           the ip
@return the upstream
shenyu-loadbalancer/src/main/java/org/apache/shenyu/loadbalancer/spi/AbstractLoadBalancer.java