public void setSolrUrl(String url) {

    LOGGER.debug("Setting solrUrl to {}", url);
    if (url != null) {
      if (solrUrl == null
          || !StringUtils.equalsIgnoreCase(url.trim(), solrUrl.getResolvedString())) {
        solrUrl = new PropertyResolver(url.trim());

        List<SolrServer> servers = new ArrayList<>(coreSolrServers.values());
        coreSolrServers.clear();
        for (SolrServer server : servers) {
          server.shutdown();
        }
      }
    } else {
      // sets to null
      solrUrl = new PropertyResolver(url);
    }
  }