code: public List<String> getGroups(String user) throws IOException {
      if (!mCacheEnabled) {
        return mService.getGroups(user);
      }
      try {
        return mCache.get(user);
      } catch (ExecutionException e) {
        throw new IOException(e);
      }
    }
docs: Gets a list of groups for the given user.
  
  @param user user name
  @return the list of groups that the user belongs to