是否可以在 SessionScoped CDI bean 中 @Observes 由异步无状态 EJB 生成的事件？

Question

在完成长时间的用户上传处理后，我需要接收一个事件。我需要为用户会话设置返回值，以便我可以正确地显示它。我正在尝试做一些 CDI 魔术，如下所述：http://piotrnowicki.com/2013/05/asynchronous-cdi-events/#toc-solution-3-ejb-producer-and-cdi-consumer (Async EJB Producer -> CDI Consumer)。

第一次尝试

来电者和接收者：

@SessionScoped
public class UploadController implements Serializable {
    private static final long serialVersionUID = 1L;

    private final Logger logger = Logger.getLogger(this.getClass());

    @EJB
    private StatelessBeanLocal statelessBean;

    @Inject
    private SomeSessionCdi cdi;

    private Future<UploadedDTO> futureDto;

    public void observeUpload(@Observes(during = TransactionPhase.AFTER_COMPLETION) UploadFinishedEvent event) {
        logger.trace("Recived CDI event: %s", event);
        // FIXME: without @SessionScoped i'm reaching here, but futureDto == null
        cdi.setStateAfterUpload(dto);
    }

    public void upload(ByteArrayOutputStream baos, User user, UploadedFileInfo info) {
        logger.trace("Initiating an async upload processing of %s", info);
        futureDto = statelessBean.upload(baos, user);
        logger.trace("Initialized an async upload processing of %s", info);
    }

}

处理器：

@Stateless
public class StatelessBean implements StatelessBeanLocal {

    @Inject
    private transient Event<UploadFinishedEvent> eventTrigger;

    @Asynchronous
    public Future<UploadedDTO> upload(ByteArrayOutputStream baos, User user) {
        UploadedEntity entity = Unpacker.unpackBaos(baos);
        logger.trace("Uploaded file for: %s", entity);
        // [..] Long processing here
        // Invoking Thread.sleep(5000); to simulate a long process
        Thread.sleep(5000);

        UploadedDTO dto = null; // here a real value, of course
        logger.debug("Finished processing of upload for: %s", entity);
        eventTrigger.fire(new UploadFinishedEventImpl());
        logger.trace("After firing a CDI event for finished upload for: %s", entity);
        return new AsyncResult<>(dto);
    }

    // [..]
}

如果 CDI bean 有 @SessionScoped 注释，那么我得到：SEVERE: WELD-000401 Failure while notifying an observer of event org.example.StatelessBean$UploadFinishedEventImpl@54c03555

如果 CDI bean 没有 @SessionScoped 注释，那么我得到了 futureDto == null

第二次尝试

将 EJB bean 更改为更改日志但仍然无效：

更改了无状态 EJB：

@Stateless
public class StatelessBean implements StatelessBeanLocal {

    @Inject
    private transient Event<UploadFinishedEvent> eventTrigger;

    @Resource
    private SessionContext sctx;

    @Asynchronous
    public Future<UploadedDTO> upload(ByteArrayOutputStream baos, User user) {
        UploadedEntity entity = Unpacker.unpackBaos(baos);
        logger.trace("Uploaded file for: %s", entity);
        // [..] Long processing here
        // Invoking Thread.sleep(5000); to simulate a long process
        Thread.sleep(5000);

        UploadedDTO dto = null; // here a real value, of course
        logger.debug("Finished processing of upload for: %s", entity);
        sctx.getBusinessObject(TemplateSetBeanLocal.class).fireUploadFinished();
        logger.trace("After firing a CDI event for finished upload for: %s", entity);
        return new AsyncResult<>(dto);
    }

    @Asynchronous
    public void fireUploadFinished() {
        logger.debug("Before firing an UploadFinishedEvent: %s", sctx.getCallerPrincipal().toString());
        eventTrigger.fire(new UploadFinishedEventImpl());
        logger.debug("After firing an UploadFinishedEvent: %s", sctx.getCallerPrincipal().toString());
    }

    // [..]
}

日志：

FINE：完成上传处理：[sample-0.1.0-SNAPSHOT.zip,application/zip,75,80KB,3cgvet] 最好：触发 CDI 事件以完成上传后：[sample-0.1.0-SNAPSHOT.zip,application/zip,75,80KB,3cgvet] FINE：在触发 UploadFinishedEvent 之前：admin FINE：触发 UploadFinishedEvent 后：admin 严重：没有用于注入 org.example.UploadController 的有效 EE 环境 最好：收到 CDI 事件：org.example.StatelessBean$UploadFinishedEventImpl@72514572

有可能吗？

Answer 1

是的，这是可能的。 没有@SessionScoped，bean 会再次创建，因此futureDTO 为空。 使用@SessionScoped @AfterCompletion，您将在事务提交后进行处理。您得到的焊接错误可能是由于某些事务行为。虽然不在示例中，但您可能正在调用另一个 EJB 方法来处理 observeUpload() 中的 uploadDTO，导致 committed 事务 (@AfterCompletion) 被挂起和恢复，这是不可能的。解决方案是使用有效事务进入观察者方法，或者在该方法中不进行任何事务处理。有时，具有适当事务上下文的额外层/方法会有所帮助。

Answer 2

不妨试试这样的：

@SessionScoped
public class UploadController implements Serializable {
    private static final long serialVersionUID = 1L;

    private final Logger logger = Logger.getLogger(this.getClass());

    @EJB
    private StatelessBeanLocal statelessBean;

    private Future<UploadedDTO> futureDto;

    public void uploadEnded(UploadedDTO dto) {
        logger.trace("Uploaded " + dto);
    }

    public void upload(ByteArrayOutputStream baos, User user, UploadedFileInfo info) {
        logger.trace("Initiating an async upload processing of %s", info);
        futureDto = statelessBean.upload(baos, user, this);
        logger.trace("Initialized an async upload processing of %s", info);
    }

}

EJB：

@Stateless
public class StatelessBean implements StatelessBeanLocal {

    @Asynchronous
    public Future<UploadedDTO> upload(ByteArrayOutputStream baos, User user, UploadController controller) {
        UploadedEntity entity = Unpacker.unpackBaos(baos);
        logger.trace("Uploaded file for: %s", entity);
        // [..] Long processing here
        // Invoking Thread.sleep(5000); to simulate a long process
        Thread.sleep(5000);

        UploadedDTO dto = null; // here a real value, of course
        logger.debug("Finished processing of upload for: %s", entity);
        controller.uploadEnded(dto);
        logger.trace("After firing a CDI event for finished upload for: %s", entity);
        return new AsyncResult(dto);
    }

    // [..]
}