public ServerName getRegionServerOfRegion(RegionInfo regionInfo) {
    RegionStateNode regionNode = getRegionStateNode(regionInfo);
    if (regionNode != null) {
      regionNode.lock();
      try {
        ServerName server = regionNode.getRegionLocation();
        return server != null ? server : regionNode.getLastHost();
      } finally {
        regionNode.unlock();
      }
    }
    return null;
  }
Returns True if region is offline (In OFFLINE or CLOSED state).
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionStates.java