code: @Override
      public void postInitModule() throws ModuleInitializationException {
          ConnectionPoolManager mgr =
                  (ConnectionPoolManager) getServer()
                          .getModule("org.fcrepo.server.storage.ConnectionPoolManager");
          if (mgr == null) {
              throw new ModuleInitializationException("ConnectionPoolManager module not loaded.",
                                                      getRole());
          }
          try {
              m_pidGenerator = new DBPIDGenerator(mgr.getPool(), m_oldPidGenDir);
          } catch (Exception e) {
              String msg = "Can't get default connection pool";
              logger.error(msg, e);
              throw new ModuleInitializationException(msg, getRole());
          }
      }
docs: Get a reference to the ConnectionPoolManager so we can give the instance
  constructor a ConnectionPool later in initializeIfNeeded().