}
public void register(String sessionId, Object principal, OnlineActivity newActivity) {
OnlineActivityBean existed = (OnlineActivityBean) getOnlineActivity(sessionId);
if (null != existed) {
existed.addRemark(" expired with replacement.");
remove(sessionId);
}
sessionIds.put(sessionId, newActivity);
Set<String> sessionsUsedByPrincipal = principals.get(principal);
if (sessionsUsedByPrincipal == null) {