private static void saveDB(){
		try{
			java.io.OutputStream ous=new java.io.FileOutputStream(dbFileName);
			java.io.ObjectOutputStream oos=new ObjectOutputStream(ous);
			oos.writeObject(userDB);
			oos.flush();
			ous.close(); 
			 LogTools.INFO(UserDao.class, "ˢļɹ");
		}catch(Exception ef){
			 LogTools.ERROR(UserDao.class, "ˢļʧܣ"+ef);
		}
	}