code: @Override
      public boolean exists(String id) throws Exception {
          // try the object store first
          Session s = doGet(id);
          if (s != null) {
              try (Lock ignored = s.lock()) {
                  // wait for the lock and check the validity of the session
                  return s.isValid();
              }
          }
          // not there, so find out if session data exists for it
          return (sessionDataStore != null && sessionDataStore.exists(id));
      }
docs: Check to see if a session corresponding to the id exists.
  
  This method will first check with the object store. If it
  doesn't exist in the object store (might be passivated etc),
  it will check with the data store.
  
  @throws Exception the Exception