Play Framework 2.5 JavaAsync 抛出 CompletionException [英] Play Framework 2.5 JavaAsync throwing CompletionException

问题描述

我正在使用 Play 2.5 来构建一个简单的应用程序.为了获得更好的性能，我将 Akka 分块响应与 Java 8 CompletionStage 策略结合使用.下面是生成分块响应的代码(不使用 ComperableFuture 时它工作正常):

I'm using Play 2.5 to build a simple app. For better performance I'm using Akka chunked response with Java 8 CompletionStage strategy. Below is the code by which chunked response is getting generated(it's working fine when not using ComperableFuture):

@Singleton
public class AbstractSource {

    public Source<ByteString, ?> getChunked(String html) {

        return Source.<ByteString>actorRef(256, OverflowStrategy.dropNew())
                .mapMaterializedValue(sourceActor -> {
                    sourceActor.tell(ByteString.fromString(html), null);
                    sourceActor.tell(new Status.Success(NotUsed.getInstance()), null);
                    return null;
                });

    }

}

这是我的控制器:

And here is my controller:

@Singleton
@AddCSRFToken
public class Application extends Controller {

    @Inject
    private AbstractSource abstractSource;

    public CompletionStage<Result> index() {


        CompletionStage<Source<ByteString, ?>> source = CompletableFuture.supplyAsync(() -> 
                                                  abstractSource.getChunked(index.render(CSRF.getToken(request()).map(t -> 
                                                    t.value()).orElse("no token")).body()
                                                   )
                                                );

        return source.thenApply( chunks -> ok().chunked(chunks));

    }

}

现在，当我运行应用程序时，它会抛出以下异常:

Now when I'm running the app it's throwing following exception:

play.api.http.HttpErrorHandlerExceptions$$anon$1: Execution exception[[CompletionException: java.lang.RuntimeException: There is no HTTP Context available from here.]]
    at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:269)
    at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:195)
    at play.api.GlobalSettings$class.onError(GlobalSettings.scala:160)
    at play.api.DefaultGlobal$.onError(GlobalSettings.scala:188)
    at play.api.http.GlobalSettingsHttpErrorHandler.onServerError(HttpErrorHandler.scala:98)
    at play.core.server.netty.PlayRequestHandler$$anonfun$2$$anonfun$apply$1.applyOrElse(PlayRequestHandler.scala:99)
    at play.core.server.netty.PlayRequestHandler$$anonfun$2$$anonfun$apply$1.applyOrElse(PlayRequestHandler.scala:98)
    at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:344)
    at scala.concurrent.Future$$anonfun$recoverWith$1.apply(Future.scala:343)
    at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32)
Caused by: java.util.concurrent.CompletionException: java.lang.RuntimeException: There is no HTTP Context available from here.
    at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
    at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
    at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1592)
    at java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1582)
    at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
    at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
    at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
Caused by: java.lang.RuntimeException: There is no HTTP Context available from here.
    at play.mvc.Http$Context.current(Http.java:57)
    at play.mvc.Controller.request(Controller.java:36)
    at com.mabsisa.ui.web.controllers.Application.lambda$index$1(Application.java:31)
    at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
    ... 5 common frames omitted

我没有在任何地方使用 HTTP 上下文，所以我不明白为什么这不起作用.使用分块响应返回正常结果时，相同的代码正在工作.请帮忙解决这个问题

I'm not using HTTP context anywhere, so why this is not working I'm not getting. Same code is working when returning normal Result with chunked response. Please help with this

推荐答案

你必须在处理CompletableFuture/CompletionStage时提供HTTP执行上下文代码>.在 Scala 中，上下文信息通过隐式传递，这些在 Java 中不可用 - 这就是 Play 使用 ThreadLocal 的原因.

You have to supply the HTTP execution context when dealing with CompletableFuture / CompletionStage. In Scala the context information is passed via implicits, these are not available in Java - this is why Play uses ThreadLocal.

但是，在切换线程时您可能会丢失此信息，这就是您遇到问题的原因.您可能认为您没有访问 HTTP 上下文，但实际上您访问了 - 您正在使用 request().

However you can lose this information when switching threads and that is why you have the problem. You may think that you don't access the HTTP context but actually you do - you are using request().

因此您必须更改代码以将 supplyAsync 与 Executor 一起使用:

So you have to change your code to use supplyAsync with an Executor:

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CompletableFuture.html#supplyAsync-java.util.function.Supplier-java.util.concurrent.Executor-

从这里:

CompletableFuture.supplyAsync(() -> abstractSource.getChunked(index.render(CSRF.getToken(request()).map(t -> 
                                                    t.value()).orElse("no token")).body()
                                                   )
                                                );

为此:

CompletableFuture.supplyAsync(() -> abstractSource.getChunked(index.render(CSRF.getToken(request()).map(t -> 
                                                    t.value()).orElse("no token")).body()
                                                   )
                                                , ec.current());

其中 ec 是你的上下文:@Inject HttpExecutionContext ec;

where ec is your context: @Inject HttpExecutionContext ec;

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