Java EE 8：异步观察器（CDI 2.0）中没有事务

Question

我有点困扰一个很普遍的问题。

我在启用Java EE 8配置文件（包括CDI 2.0）的情况下运行Wildfly 12，并且正在使用JTA。

那么问题是什么：我有一个@ApplicationScoped bean会触发一个异步事件。 另一个@ApplicationScoped bean通过@ObservesAsync观察此事件。 在观察者内部，我想处理一些传播的元数据，并且还与数据库进行交互。 我有一个用@Transactional注释的存储库类。 设置如下所示：

一个简单的示例如下所示：

@ApplicationScoped
public class ClassA {

    @Inject
    private Event<ApplicationStarted> applicationStartedEvent;

    public void initialize(@Observes @Initialized(ApplicationScoped.class) Object init) {
        applicationStartedEvent.fireAsync(new ApplicationStarted());
    }
}

@ApplicationScoped
public class ClassB {

    @Inject
    private Repository repository;

    public void onApplicationStarted(@ObservesAsync ApplicationStarted applicationStarted) {

        repository.getSomethingFromDatabase();
    }
}

@Transactional
@Dependent
public class Repository {

    @PersistenceContext
    private EntityManager entityManager;

    public List<Object> getSomethingFromDatabase() {
        return entityManager.createQuery("from User").getResultList();
    }
}

不幸的是，我无法获得此代码片段。 我不明白什么时候有一个奇怪的例外

repository.getSomethingFromDatabase();

被执行。

17:17:53,611 ERROR [stderr] (Weld Thread Pool -- 3) java.lang.NullPointerException
17:17:53,611 ERROR [stderr] (Weld Thread Pool -- 3)     at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:936)
17:17:53,611 ERROR [stderr] (Weld Thread Pool -- 3)     at org.wildfly.common.context.ContextManager.getPrivileged(ContextManager.java:271)
17:17:53,611 ERROR [stderr] (Weld Thread Pool -- 3)     at org.wildfly.transaction.client.LocalTransactionContext.getCurrent(LocalTransactionContext.java:115)
17:17:53,612 ERROR [stderr] (Weld Thread Pool -- 3)     at org.wildfly.transaction.client.ContextTransactionManager.begin(ContextTransactionManager.java:62)
17:17:53,612 ERROR [stderr] (Weld Thread Pool -- 3)     at org.wildfly.transaction.client.ContextTransactionManager.begin(ContextTransactionManager.java:54)
17:17:53,612 ERROR [stderr] (Weld Thread Pool -- 3)     at com.arjuna.ats.jta.cdi.transactional.TransactionalInterceptorBase.invokeInOurTx(TransactionalInterceptorBase.java:116)
17:17:53,612 ERROR [stderr] (Weld Thread Pool -- 3)     at com.arjuna.ats.jta.cdi.transactional.TransactionalInterceptorRequired.doIntercept(TransactionalInterceptorRequired.java:53)
17:17:53,612 ERROR [stderr] (Weld Thread Pool -- 3)     at com.arjuna.ats.jta.cdi.transactional.TransactionalInterceptorBase.intercept(TransactionalInterceptorBase.java:79)
17:17:53,613 ERROR [stderr] (Weld Thread Pool -- 3)     at com.arjuna.ats.jta.cdi.transactional.TransactionalInterceptorRequired.intercept(TransactionalInterceptorRequired.java:47)
17:17:53,613 ERROR [stderr] (Weld Thread Pool -- 3)     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
17:17:53,613 ERROR [stderr] (Weld Thread Pool -- 3)     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
17:17:53,614 ERROR [stderr] (Weld Thread Pool -- 3)     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
17:17:53,614 ERROR [stderr] (Weld Thread Pool -- 3)     at java.lang.reflect.Method.invoke(Method.java:498)
17:17:53,614 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.interceptor.reader.SimpleInterceptorInvocation$SimpleMethodInvocation.invoke(SimpleInterceptorInvocation.java:73)
17:17:53,614 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.interceptor.proxy.InterceptorMethodHandler.executeAroundInvoke(InterceptorMethodHandler.java:84)
17:17:53,614 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.interceptor.proxy.InterceptorMethodHandler.executeInterception(InterceptorMethodHandler.java:72)
17:17:53,614 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.interceptor.proxy.InterceptorMethodHandler.invoke(InterceptorMethodHandler.java:56)
17:17:53,614 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.bean.proxy.CombinedInterceptorAndDecoratorStackMethodHandler.invoke(CombinedInterceptorAndDecoratorStackMethodHandler.java:79)
17:17:53,615 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.bean.proxy.CombinedInterceptorAndDecoratorStackMethodHandler.invoke(CombinedInterceptorAndDecoratorStackMethodHandler.java:68)
17:17:53,615 ERROR [stderr] (Weld Thread Pool -- 3)     at com.auroraspotter.kp.Repo$Proxy$_$$_WeldSubclass.getSomethingFromDatabase(Unknown Source)
17:17:53,615 ERROR [stderr] (Weld Thread Pool -- 3)     at com.auroraspotter.kp.KpIndexUpdateCronControl.onApplicationStarted(KpIndexUpdateCronControl.java:48)
17:17:53,615 ERROR [stderr] (Weld Thread Pool -- 3)     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
17:17:53,616 ERROR [stderr] (Weld Thread Pool -- 3)     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
17:17:53,616 ERROR [stderr] (Weld Thread Pool -- 3)     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
17:17:53,616 ERROR [stderr] (Weld Thread Pool -- 3)     at java.lang.reflect.Method.invoke(Method.java:498)
17:17:53,616 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.injection.StaticMethodInjectionPoint.invoke(StaticMethodInjectionPoint.java:95)
17:17:53,617 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.injection.StaticMethodInjectionPoint.invoke(StaticMethodInjectionPoint.java:85)
17:17:53,617 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.injection.MethodInvocationStrategy$DefaultMethodInvocationStrategy.invoke(MethodInvocationStrategy.java:109)
17:17:53,617 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.event.ObserverMethodImpl.sendEvent(ObserverMethodImpl.java:330)
17:17:53,617 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.event.ObserverMethodImpl.sendEvent(ObserverMethodImpl.java:308)
17:17:53,617 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.event.ObserverMethodImpl.notify(ObserverMethodImpl.java:286)
17:17:53,617 ERROR [stderr] (Weld Thread Pool -- 3)     at javax.enterprise.inject.spi.ObserverMethod.notify(ObserverMethod.java:124)
17:17:53,617 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.util.Observers.notify(Observers.java:170)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.event.ObserverNotifier.notifyAsyncObserver(ObserverNotifier.java:413)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.event.ObserverNotifier.lambda$notifyAsyncObservers$5(ObserverNotifier.java:356)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.event.ObserverNotifier.lambda$null$8(ObserverNotifier.java:438)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.security.spi.SecurityServices.lambda$getSecurityContextAssociator$0(SecurityServices.java:80)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.weld.event.ObserverNotifier.lambda$createSupplier$9(ObserverNotifier.java:435)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at java.util.concurrent.CompletableFuture$AsyncSupply.run$$$capture(CompletableFuture.java:1590)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java)
17:17:53,618 ERROR [stderr] (Weld Thread Pool -- 3)     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
17:17:53,619 ERROR [stderr] (Weld Thread Pool -- 3)     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
17:17:53,619 ERROR [stderr] (Weld Thread Pool -- 3)     at java.lang.Thread.run(Thread.java:748)
17:17:53,619 ERROR [stderr] (Weld Thread Pool -- 3)     at org.jboss.threads.JBossThread.run(JBossThread.java:485)

如果我在同步事件中运行相同的代码，则一切正常。

那我想念什么呢？

Answer 1

我终于找到了解决方案。

由于观察者很困惑，因此没有可用的容器管理的事务（这非常明智，因为该事务不能跨越多个线程）。 因此，我需要自己开始交易。

不幸的是，这也不起作用。 经过数小时的调试，我终于找到了根本原因。 由于某种原因，Wildfly的ContextManager抛出了NPE，因为观察者类（ClassB）中没有可用的类加载器。 幸运的是，已有针对模块wildfly-common的错误修复。 所以我刚刚从1.3.0.Final版本升级到1.3.1.Final。 最终代码如下所示：

@ApplicationScoped
public class Observer {

    @Inject
    private Repository repository;

    public void onApplicationStarted(@ObservesAsync ApplicationStarted applicationStarted) throws Exception {
        UserTransaction userTransaction = (UserTransaction) new InitialContext().lookup("java:jboss/UserTransaction");
        userTransaction.begin();
        try {
            repository.getSomethingFromDatabase();
            // or repository.persistSomething();
        } catch (Exception e) {
            e.printStackTrace();
        }
        userTransaction.commit();
    }
}