@Override
	public String execute() throws Exception {
		HttpSession session = ServletActionContext.getRequest().getSession();
		User user = (User) session.getAttribute(com.ccf.action.user.UserLoginAction.USER_SESSION);
		if (user == null)
			return LOGIN;
		
		if (action == null || cid == null || sender == null || receiver == null)
			return "null";
		
		if (!this.service.verifyLeader(Integer.parseInt(cid), user.getUid()))	// if current user isn't the leader
			return LOGIN;
		
		
		// sender means applicant, why? cuz that's him sent out this join_club_apply
		if (action.equals("approve")) {
			// let that guy be a member first
			this.service.addANewMember(Integer.parseInt(cid), Integer.parseInt(sender));
			// then send a newbie-message to every old member, update relative's notification
			this.service.approveJoinClubApply(Integer.parseInt(cid), Integer.parseInt(sender));
			return SUCCESS;
		}
			
		if (action.equals("reject")) {
			this.service.rejectJoinClubApply(Integer.parseInt(cid), Integer.parseInt(sender));
			return SUCCESS;
		}
		return ERROR;
	}