https://github.com/gnu11111/ktor-4164-test

#ktor-2.0 #issue #classloader #classcast #exception
https://github.com/gnu11111/ktor-4164-test

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#ktor-2.0 #issue #classloader #classcast #exception

• Host: GitHub
• URL: https://github.com/gnu11111/ktor-4164-test
• Owner: gnu11111
• Created: 2022-05-09T11:31:33.000Z (about 4 years ago)
• Default Branch: master
• Last Pushed: 2022-05-09T12:04:03.000Z (about 4 years ago)
• Last Synced: 2025-02-09T05:27:43.870Z (over 1 year ago)
• Language: Kotlin
• Size: 286 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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# [KTOR-4164: Different ClassLoader behaviour in Ktor-2.0.0 (vs. Ktor-1.6.x) produces a ClassCastException within a CouroutineScope](https://youtrack.jetbrains.com/issue/KTOR-4164)

In a CoroutineScope of a Ktor-2.0.0-application (netty-engine), the "ClassLoaders@AppClassLoader" is not aware of Objects loaded by the (default?) Application ClassLoader. Therefore, for exampe, received objects from an (Apache-ActiveMQ-Artemis-)message-queue cannot be cast to its corresponding DTOs - see attached screenshots with Ktor-1.6.8/Kotlin-1.6.10 vs. Ktor-2.0.0/Kotlin-1.6.20.

![ClassLoder with Ktor-1.6.8](ClassLoaderKtor_1_6_8.png) ![ClassLoder with Ktor-2.0.0](ClassLoaderKtor_2_0_0.png)

# To reproduce the error:

1) get and start the Apache ActiveMQ Artemis - message broker:



wget https://downloads.apache.org/activemq/activemq-artemis/2.22.0/apache-artemis-2.22.0-bin.tar.gz


tar xfz apache-artemis-2.22.0-bin.tar.gz

apache-artemis-2.22.0/bin/artemis create ktor-test # username: test / password: test / anonymous access: Y

ktor-test/bin/artemis run



2) either run the `com.example.ApplicationTest` or run the Ktor-application in "development"-mode (`-Dio.ktor.development=true`) and start the `com.example.MessageProducer` afterwards.

**FYI: Everything works fine in "normal"-mode (`-Dio.ktor.development=false`) and the class cast exception doesn't occur!**



2022-05-09 13:14:23.841 [DefaultDispatcher-worker-1] INFO  ktor.application - Received Test object as JSON message: Test(id=1)

Exception in thread "DefaultDispatcher-worker-1" java.lang.ClassCastException: class com.example.dto.Test cannot be cast to class com.example.dto.Test (com.example.dto.Test is in unnamed module of loader 'app'; com.example.dto.Test is in unnamed module of loader io.ktor.server.engine.OverridingClassLoader$ChildURLClassLoader @1c7696c6)

	at com.example.plugins.MessageQueueKt$configureMessageQueue$1.invokeSuspend(MessageQueue.kt:39)

	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)

	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106)

	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:570)

	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:749)

	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:677)

	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:664)

	Suppressed: kotlinx.coroutines.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@561bd503, Dispatchers.Default]