对话过期跳到登录界面

public String detect() throws Exception{
		String currentUser = (String)getSession().get("currentUser");
		if(currentUser==null){
			log.info("session is timeout");
			returnPageURL = "/timeoutRedirect.jsp";
			return "redirect";
		}
		
		log.info("session is not timeout");
		
		returnPageURL = "/system/detect/computer_detect.jsp";
		return "dispatcher";
	}

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