要求仅必须允许单个线程执行用户管理（创建/更新/导入）操作，但不允许多个线程同时为同一用户执行用户操作。例如，当线程A正在创建用户A时，必须不允许线程B同时允许线程B导入用户A或创建用户A，但是允许线程B导入用户B。下面的代码线程对于这些要求是否安全？

public class UserManagement {

    ConcurrentHashMap<Integer, Lock> userLock = new ConcurrentHashMap<>();

    public void createUser(User user, Integer userId) {
        Lock lock = userLock.putIfAbsent(userId, new ReentrantLock());
        try {
            lock.lock();
            //create user logic
        } finally {
            lock.unlock();
        }
    }

    public void importUser(User user, Integer userId) {
        Lock lock = userLock.putIfAbsent(userId, new ReentrantLock());
        try {
            lock.lock();
            //import user logic
        } finally {
            lock.unlock();
        }
    }

    public void updateUser(User user, Integer userId) {
        Lock lock = userLock.putIfAbsent(userId, new ReentrantLock());
        try {
            lock.lock();
            // update user logic
        } finally {
            lock.unlock();
        }
    }
}