Java EE 8 : No transaction in asynchronous observer (CDI 2. 0)

Question

我有点遇到一个问题，我猜这个问题很常见。

我运行启用了 Java EE 8 配置文件(包括 CDI 2.0)的 Wildfly 12，并且使用 JTA。

那么问题是什么:我有一个触发异步事件的 @ApplicationScoped bean。另一个@ApplicationScoped bean 通过@ObservesAsync 观察此事件。在观察者中，我想处理一些传播的元数据并与数据库交互。我有一个用 @Transactional 注释的存储库类。设置如下所示:

一个简单的例子如下所示:

@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();
    }
}

不幸的是我无法让这个代码片段工作。有一个奇怪的异常，我不明白什么时候

repository.getSomethingFromDatabase();

已执行。

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)

如果我使用同步事件运行相同的代码，一切都会正常。

那么我错过了什么？

Answer 1

我终于找到了解决办法。

由于观察者是异步的，因此没有可用的容器管理事务(这绝对有意义，因为事务无法跨越多个线程)。所以我需要自己开始交易。

不幸的是，这也不起作用。经过几个小时的调试，我终于找到了根本原因。由于某种原因，Wildfly 的 ContextManager 抛出了一个 NPE，因为观察者类 (ClassB) 中没有可用的类加载器。幸运的是，wildfly-common 模块已经有一个错误修复程序。所以我刚刚从版本1.3.0.Final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();
    }
}