Play Framework 2.5.4 异步休眠操作

Question

如何使用 Akka 在使用 Hibernate 的数据库上执行操作而不阻止 Web 客户端？

更新：

原来错误是由 dao.get() 方法引起的。我更改了 start() 方法以获取实际对象而不是数据库中的 id，现在我没有收到任何错误，但什么也没有发生（如我之前所说，它卡在 em.merge() 上）。

public CompletionStage<Result> start(SomeObject object) {
    ExecutionContext ec = Akka.system().dispatchers().lookup("akka.actor.db-context");
    return CompletableFuture.supplyAsync(() -> doStuff(object), play.libs.concurrent.HttpExecution.fromThread(ec))
            .thenApply(i -> ok("Got result: " + i));
}

已过时：

如果我尝试类似的操作：

@Transactional
public CompletionStage<Result> start(Long id) {
    ExecutionContext ec = Akka.system().dispatchers().lookup("akka.actor.db-context");
    return CompletableFuture.supplyAsync(() -> doStuff(dao.get(id)), play.libs.concurrent.HttpExecution.fromThread(ec))
            .thenApply(i -> ok("Got result: " + i));
}

doStuff 仅执行 entityManager.merge()，我得到：

[CompletionException: org.hibernate.SessionException: Session is closed!]

或

[CompletionException: java.lang.IllegalStateException: EntityManager is closed]

当我使用下面的代码启动上面的过程时：

@Transactional
public Result mainMethod() {
    List<SomeObject> allObjects= dao.getAll();
    int size = allObjects.size();
    for(int i = 0; i < size; i++) {
        start(allObjects.get(i).getId());
    }
    return ok("Started");
}

然后新创建的线程（参与者）在尝试数据库操作时进入无限循环。

谢谢！

完整的堆栈跟踪：

play.api.http.HttpErrorHandlerExceptions$$anon: Execution exception[[CompletionException: org.hibernate.SessionException: Session is closed!]] at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:280) at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:206) at play.api.GlobalSettings$class.onError(GlobalSettings.scala:160) at play.api.DefaultGlobal$.onError(GlobalSettings.scala:188) at play.api.http.GlobalSettingsHttpErrorHandler.onServerError(HttpErrorHandler.scala:98) at play.core.server.netty.PlayRequestHandler$$anonfun$$anonfun$apply.applyOrElse(PlayRequestHandler.scala:100) at play.core.server.netty.PlayRequestHandler$$anonfun$$anonfun$apply.applyOrElse(PlayRequestHandler.scala:99) at scala.concurrent.Future$$anonfun$recoverWith.apply(Future.scala:344) at scala.concurrent.Future$$anonfun$recoverWith.apply(Future.scala:343) at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32) at play.api.libs.iteratee.Execution$trampoline$.executeScheduled(Execution.scala:109) at play.api.libs.iteratee.Execution$trampoline$.execute(Execution.scala:71) at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:40) at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:248) at scala.concurrent.Promise$class.complete(Promise.scala:55) at scala.concurrent.impl.Promise$DefaultPromise.complete(Promise.scala:153) at scala.concurrent.java8.FuturesConvertersImpl$P.accept(FutureConvertersImpl.scala:94) at scala.concurrent.java8.FuturesConvertersImpl$P.accept(FutureConvertersImpl.scala:89) at java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:760) at java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:736) at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:474) at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1595) at play.core.j.HttpExecutionContext$$anon.run(HttpExecutionContext.scala:56) at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:39) at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:405) at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) Caused by: java.util.concurrent.CompletionException: org.hibernate.SessionException: Session is closed! at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273) at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280) at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1592) ... 7 common frames omitted Caused by: org.hibernate.SessionException: Session is closed! at org.hibernate.internal.AbstractSessionImpl.errorIfClosed(AbstractSessionImpl.java:133) at org.hibernate.internal.SessionImpl.setCacheMode(SessionImpl.java:1455) at org.hibernate.jpa.spi.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:1144) at org.hibernate.jpa.spi.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:1068) at daos.dao.get(dao.java:45) at controllers.DemoController.lambda$start[=16=](DemoController.java:195) at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590) ... 7 common frames omitted

LE:

尝试过：

ExecutionContext ec = Akka.system().dispatchers().lookup("akka.actor.db-context");
return CompletableFuture.supplyAsync(() -> jpa.withTransaction("default", true, ()-> doStuff(dao.get(id))), play.libs.concurrent.HttpExecution.fromThread(ec))
                .thenApply(i -> ok("Got result: " + i));

我得到了同样的错误。

Answer 1

@Transactional 注解在同步方法上。我想您需要在异步块中进行交易。您可以使用 for jpa 方法 withTransaction 而不是注释。它的签名（来自Play java api）

/**
 * Run a block of code in a JPA transaction.
 *
 * @param name The persistence unit name
 * @param readOnly Is the transaction read-only?
 * @param block Block of code to execute
 * @param <T> type of result
 * @return code execution result
 */
public <T> T withTransaction(String name, boolean readOnly, Supplier<T> block);

应该是这样的：

在控制器中注入JPAApi：
```
@Inject
JPAApi jpa;
```

通过调用 jpa 实现异步执行器：

 jpa.withTransaction("default", true, ()->doStuff(dao.get(id)), play.libs.concurrent.HttpExecution.fromThread(ec))
    .thenApply(i -> ok("Got result: " + i)));

请注意 withTransaction 调用中的第二个参数 true 用于只读操作（在您的情况下）。

更改 DAO class 以使用注入的 JPAAPi。

Answer 2

我按照@asch 的建议解决了这个问题：

控制器：

    @Inject
    private JPAApi jpa;
    [...]
    return CompletableFuture.supplyAsync(() -> jpa.withTransaction("default", false, ()-> doStuff(objectDAO.get(id))), play.libs.concurrent.HttpExecution.fromThread(ec))
                .thenApply(i -> ok("Got result: " + i));

并且在 doStuff 方法中 class:

    private static final JPAApi jpaApi = Play.current().injector().instanceOf(JPAApi.class);
    [...]
    jpaApi.withTransaction(() -> {
        EntityManager em = jpaApi.em();
        em.merge(object);
    });
    [...]

Play Framework 2.5.4 异步休眠操作

Play Framework 2.5.4 Async Hibernate operations

java

hibernate

playframework

playframework-2.5