kotlin - java.lang.UnsupportedOperationException: Reflective setAccessible(true) disabled

Question

When I run my Ktor application with gradle run then I've got the following exception:

19:21:11.795 [main] DEBUG io.netty.util.internal.logging.InternalLoggerFactory - Using SLF4J as the default logging framework
19:21:11.810 [main] DEBUG io.netty.util.internal.PlatformDependent0 - -Dio.netty.noUnsafe: false
19:21:11.810 [main] DEBUG io.netty.util.internal.PlatformDependent0 - Java version: 11
19:21:11.811 [main] DEBUG io.netty.util.internal.PlatformDependent0 - sun.misc.Unsafe.theUnsafe: available
19:21:11.812 [main] DEBUG io.netty.util.internal.PlatformDependent0 - sun.misc.Unsafe.copyMemory: available
19:21:11.812 [main] DEBUG io.netty.util.internal.PlatformDependent0 - java.nio.Buffer.address: available
19:21:11.814 [main] DEBUG io.netty.util.internal.PlatformDependent0 - direct buffer constructor: unavailable
java.lang.UnsupportedOperationException: Reflective setAccessible(true) disabled
        at io.netty.util.internal.ReflectionUtil.trySetAccessible(ReflectionUtil.java:31)
        at io.netty.util.internal.PlatformDependent0$4.run(PlatformDependent0.java:225)
        at java.base/java.security.AccessController.doPrivileged(Native Method)
        at io.netty.util.internal.PlatformDependent0.<clinit>(PlatformDependent0.java:219)
        at io.netty.util.internal.PlatformDependent.isAndroid(PlatformDependent.java:273)
        at io.netty.util.internal.PlatformDependent.<clinit>(PlatformDependent.java:92)
        at io.netty.channel.epoll.Native.loadNativeLibrary(Native.java:225)
        at io.netty.channel.epoll.Native.<clinit>(Native.java:57)
        at io.netty.channel.epoll.Epoll.<clinit>(Epoll.java:39)
        at io.ktor.server.netty.EventLoopGroupProxy$Companion.create(NettyApplicationEngine.kt:189)
        at io.ktor.server.netty.NettyApplicationEngine.<init>(NettyApplicationEngine.kt:74)
        at io.ktor.server.netty.EngineMain.main(EngineMain.kt:22)
19:21:11.814 [main] DEBUG io.netty.util.internal.PlatformDependent0 - java.nio.Bits.unaligned: available, true
19:21:11.815 [main] DEBUG io.netty.util.internal.PlatformDependent0 - jdk.internal.misc.Unsafe.allocateUninitializedArray(int): unavailable
java.lang.IllegalAccessException: class io.netty.util.internal.PlatformDependent0$6 cannot access class jdk.internal.misc.Unsafe (in module java.base) because module java.base does not export jdk.internal.misc to unnamed module @557caf28
        at java.base/jdk.internal.reflect.Reflection.newIllegalAccessException(Reflection.java:361)
        at java.base/java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:591)
        at java.base/java.lang.reflect.Method.invoke(Method.java:558)
        at io.netty.util.internal.PlatformDependent0$6.run(PlatformDependent0.java:335)
        at java.base/java.security.AccessController.doPrivileged(Native Method)
        at io.netty.util.internal.PlatformDependent0.<clinit>(PlatformDependent0.java:326)
        at io.netty.util.internal.PlatformDependent.isAndroid(PlatformDependent.java:273)
        at io.netty.util.internal.PlatformDependent.<clinit>(PlatformDependent.java:92)
        at io.netty.channel.epoll.Native.loadNativeLibrary(Native.java:225)
        at io.netty.channel.epoll.Native.<clinit>(Native.java:57)
        at io.netty.channel.epoll.Epoll.<clinit>(Epoll.java:39)
        at io.ktor.server.netty.EventLoopGroupProxy$Companion.create(NettyApplicationEngine.kt:189)
        at io.ktor.server.netty.NettyApplicationEngine.<init>(NettyApplicationEngine.kt:74)
        at io.ktor.server.netty.EngineMain.main(EngineMain.kt:22)

the content of build.gradle.kts file

plugins {
    application
    kotlin("jvm") version "1.3.61"
}

group = "io.flatmap"
version = "1.0-SNAPSHOT"


val ktor_version = "1.3.0"

repositories {
    mavenCentral()
    jcenter()
}

dependencies {
    implementation(kotlin("stdlib-jdk8"))
    compile("io.ktor:ktor-server-netty:$ktor_version")
    compile("io.ktor:ktor-server-core:$ktor_version")
    compile("ch.qos.logback:logback-classic:1.2.3")
    testCompile(group = "junit", name = "junit", version = "4.12")
}

tasks {
    compileKotlin {
        kotlinOptions.jvmTarget = "11"
    }
    compileTestKotlin {
        kotlinOptions.jvmTarget = "11"
    }
}

application {
    mainClassName = "io.ktor.server.netty.EngineMain"
}

I am using Zulu OpenJDK 11:

 java --version
openjdk 11.0.6 2020-01-14 LTS
OpenJDK Runtime Environment Zulu11.37+17-CA (build 11.0.6+10-LTS)
OpenJDK 64-Bit Server VM Zulu11.37+17-CA (build 11.0.6+10-LTS, mixed mode) 

What am I doing wrong?

Answer 1

The access level of each object member cannot be increased anymore. The operation is not allowed anymore since Java 9 and has been hardly disabled in release 11.

You need to run this application with Java 8.

See https://www.oracle.com/technetwork/java/javase/9-relnote-issues-3704069.html (search for "setAccessible"). There is a new Object which must now be used to allow it again: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/reflect/AccessibleObject.html