java - 使用@Async 嵌套@Transactional 方法

Question

我将 Spring 与 JPA 一起使用。我打开了 @EnableAsync 和 @EnableTransactionManagement。在我的用户注册服务方法中，我调用了一些其他的服务方法，它们被注释为 @Async。这些方法可以做各种各样的事情，比如发送欢迎电子邮件和向我们的第三方支付系统注册新用户。

在我想验证第三方支付系统是否成功创建用户之前，一切正常。此时，@Async 方法会尝试创建一个 UserAccount(它引用新生成的 User)并使用 出错javax.persistence.EntityNotFoundException:无法找到 com.dk.st.model.User 的 id 为 2017

注册调用如下所示:

private User registerUser(User newUser, Boolean waitForAccount) {
    String username = newUser.getUsername();
    String email = newUser.getEmail();

    // ... Verify the user doesn't already exist

    // I have tried all manner of flushing and committing right here, nothing works
    newUser = userDAO.merge(newUser);

    // Here is where we register the new user with the payment system.
    // The User we just merged is not /actually/ in the DB
    Future<Customer> newCustomer = paymentService.initializeForNewUser(newUser);
    // Here is where I occasionally (in test methods) pause this thread to wait
    // for the successful account creation.
    if (waitForAccount) {
        try {
            newCustomer.get();
        } catch (Exception e) {
            logger.error("Exception while creating user account!", e);
        }
    }

    // Do some other things that may or may not be @Aysnc

    return newUser;
}

支付服务调用它来完成注册用户的工作，如下所示:

@Async
@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
public Future<Customer> initializeForNewUser(User newUser) {
    // ... Set up customerParams

    Customer newCustomer = null;
    try {
        newCustomer = Customer.create(customerParams);

        UserAccount newAccount = new UserAccount();
        newAccount.setUser(newUser);
        newAccount.setCustomerId(newCustomer.getId());
        newAccount.setStatus(AccountStatus.PRE_TRIAL);

        // When merging, JPA cannot find the newUser object in the DB and complains
        userAccountDAO.merge(newAccount);
    } catch (Exception e) {
        logger.error("Error while creating UserAccount!", e);
        throw e;
    }

    return new AsyncResult<Customer>(newCustomer);
}

列出的 StackOverflow 答案 here建议我设置一个 REQUIRES_NEW 传播，我已经这样做了，但没有这样的运气。

谁能指出我正确的方向？我真的不想直接从我的 Controller 方法调用 paymentService 。我觉得这肯定是服务级别的调用。

感谢您的帮助!

Answer 1

在 Vyncent 的帮助下，这是我得出的解决方案。我创建了一个名为 UserCreationService 的新类，并将处理 User 创建的所有方法都放在该类中。这是一个例子:

@Override
public User registerUserWithProfileData(User newUser, String password, Boolean waitForAccount) {
    newUser.setPassword(password);
    newUser.encodePassword();
    newUser.setJoinDate(Calendar.getInstance(TimeZone.getTimeZone("UTC")).getTime());

    User registered = userService.createUser(newUser);
    registered = userService.processNewRegistration(registered, waitForAccount);

    return userService.setProfileInformation(registered);
}

您会注意到此方法上有 NO @Transactional 注释。这是故意的。对应的 createUser 和 processNewRegistration 定义如下所示:

@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
public User createUser(User newUser) {
    String username = newUser.getUsername();
    String email = newUser.getEmail();

    if ((username != null) && (userDAO.getUserByUsername(username) != null)) {
        throw new EntityAlreadyExistsException("User already registered: " + username);
    }

    if (userDAO.getUserByUsername(newUser.getEmail()) != null) {
        throw new EntityAlreadyExistsException("User already registered: " + email);
    }

    return userDAO.merge(newUser);
}

@Override
@Transactional(propagation = Propagation.REQUIRES_NEW)
public User processNewRegistration(
        User newUser,
        Boolean waitForAccount) 
{
    Future<UserAccount> customer = paymentService.initializeForNewUser(newUser);
    if (waitForAccount) {
        try {
            customer.get();
        } catch (Exception e) {
            logger.error("Error while creating Customer object!", e);
        }
    }

    // Do some other maintenance type things...

    return newUser;
}

Vyncent 发现事务管理是问题所在。创建其他服务使我能够更好地控制这些事务何时提交。虽然我最初对采用这种方法犹豫不决，但这是与 Spring 托管事务和代理的权衡。

我希望这可以帮助其他人在以后节省一些时间。