private void checkForClusterLevelSingleConf(String vlsClassName) {
    assert this.vlsClazzName != null;
    if (!this.vlsClazzName.equals(vlsClassName)) {
      LOG.warn("Trying to use table specific value for config "
        + "'hbase.regionserver.visibility.label.service.class' which is not supported."
        + " Will use the cluster level VisibilityLabelService class " + this.vlsClazzName);
    }
  }
@return singleton instance of {@link VisibilityLabelService}. The FQCN of the implementation
        class can be specified using "hbase.regionserver.visibility.label.service.class".
@throws IOException When VLS implementation, as specified in conf, can not be loaded.
hbase-server/src/main/java/org/apache/hadoop/hbase/security/visibility/VisibilityLabelServiceManager.java