synchronized boolean updateAccessTime() {
      if (closed) {
        return false;
      }
      if (connection.isAborted() || connection.isClosed()) {
        LOG.info("Unexpected: cached Connection is aborted/closed, removed from cache");
        connections.remove(userName);
        return false;
      }
      lastAccessTime = EnvironmentEdgeManager.currentTime();
      return true;
    }
Returns Cluster ID for the HBase cluster or null if there is an err making the connection.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/ConnectionCache.java