ubuntu - 如何使用 Kotlin 的反射？

Question

我觉得我不完全了解某些深处的深度。

$ cat blya.kt 
inline fun<reified T> omg() {
    val x = T::class.supertypes  // such an innocent init
}

fun main() {
    omg<Int>()
}

$ kotlinc -d omg.jar -include-runtime blya.kt && java -jar omg.jar
OpenJDK 64-Bit Server VM warning: Options -Xverify:none and -noverify were deprecated in JDK 13 and will likely be removed in a future release.
blya.kt:2:6: warning: variable 'x' is never used
    val x = T::class.supertypes
     ^
Exception in thread "main" kotlin.jvm.KotlinReflectionNotSupportedError: Kotlin reflection implementation is not found at runtime. Make sure you have kotlin-reflect.jar in the classpath
    at kotlin.jvm.internal.ClassReference.error(ClassReference.kt:84)
    at kotlin.jvm.internal.ClassReference.getSupertypes(ClassReference.kt:42)
    at BlyaKt.main(blya.kt:9)
    at BlyaKt.main(blya.kt)

$ ls /snap/kotlin/current/lib/kotlin-reflect.jar  -l
-rw-r--r-- 1 root root 2893798 Sep 10 13:15 /snap/kotlin/current/lib/kotlin-reflect.jar

$ # hmm, strage it's not found on default, well, ok, let's add it

$ kotlinc -classpath /snap/kotlin/current/lib/ -d omg.jar -include-runtime blya.kt && java -jar omg.jar
OpenJDK 64-Bit Server VM warning: Options -Xverify:none and -noverify were deprecated in JDK 13 and will likely be removed in a future release.
blya.kt:2:6: warning: variable 'x' is never used
    val x = T::class.supertypes
     ^
Exception in thread "main" kotlin.jvm.KotlinReflectionNotSupportedError: Kotlin reflection implementation is not found at runtime. Make sure you have kotlin-reflect.jar in the classpath
    at kotlin.jvm.internal.ClassReference.error(ClassReference.kt:84)
    at kotlin.jvm.internal.ClassReference.getSupertypes(ClassReference.kt:42)
    at BlyaKt.main(blya.kt:9)
    at BlyaKt.main(blya.kt)

$ kotlinc -classpath /snap/kotlin/current/lib/kotlin-reflect.jar -d omg.jar -include-runtime blya.kt && java -jar omg.jar
OpenJDK 64-Bit Server VM warning: Options -Xverify:none and -noverify were deprecated in JDK 13 and will likely be removed in a future release.
blya.kt:2:6: warning: variable 'x' is never used
    val x = T::class.supertypes
     ^
Exception in thread "main" kotlin.jvm.KotlinReflectionNotSupportedError: Kotlin reflection implementation is not found at runtime. Make sure you have kotlin-reflect.jar in the classpath
    at kotlin.jvm.internal.ClassReference.error(ClassReference.kt:84)
    at kotlin.jvm.internal.ClassReference.getSupertypes(ClassReference.kt:42)
    at BlyaKt.main(blya.kt:9)
    at BlyaKt.main(blya.kt)

$ kotlinc -classpath /snap/kotlin/current/lib/kotlin-reflect.jar -d omg.jar -include-runtime blya.kt && java -classpath /snap/kotlin/current/lib -jar omg.jar
OpenJDK 64-Bit Server VM warning: Options -Xverify:none and -noverify were deprecated in JDK 13 and will likely be removed in a future release.
blya.kt:2:6: warning: variable 'x' is never used
    val x = T::class.supertypes
     ^
Exception in thread "main" kotlin.jvm.KotlinReflectionNotSupportedError: Kotlin reflection implementation is not found at runtime. Make sure you have kotlin-reflect.jar in the classpath
    at kotlin.jvm.internal.ClassReference.error(ClassReference.kt:84)
    at kotlin.jvm.internal.ClassReference.getSupertypes(ClassReference.kt:42)
    at BlyaKt.main(blya.kt:9)
    at BlyaKt.main(blya.kt)

好像我根本不想使用它。
即使有详细的输出，它也假装包含它......在某种程度上。

$ kotlinc -verbose -d omg.jar -include-runtime blya.kt
OpenJDK 64-Bit Server VM warning: Options -Xverify:none and -noverify were deprecated in JDK 13 and will likely be removed in a future release.
logging: using Kotlin home directory /snap/kotlin/53
logging: configuring the compilation environment
logging: configure scripting: Added template org.jetbrains.kotlin.mainKts.MainKtsScript from [/snap/kotlin/53/lib/kotlin-main-kts.jar, /snap/kotlin/53/lib/kotlin-reflect.jar, /snap/kotlin/53/lib/kotlin-script-runtime.jar, /snap/kotlin/53/lib/kotlin-stdlib.jar]
logging: loading modules: [java.se, jdk.accessibility, jdk.attach, jdk.compiler, jdk.dynalink, jdk.httpserver, jdk.incubator.foreign, jdk.jartool, jdk.javadoc, jdk.jconsole, jdk.jdi, jdk.jfr, jdk.jshell, jdk.jsobject, jdk.management, jdk.management.jfr, jdk.net, jdk.nio.mapmode, jdk.scripting.nashorn, jdk.sctp, jdk.security.auth, jdk.security.jgss, jdk.unsupported, jdk.unsupported.desktop, jdk.xml.dom, java.base, java.compiler, java.datatransfer, java.desktop, java.xml, java.instrument, java.logging, java.management, java.management.rmi, java.rmi, java.naming, java.net.http, java.prefs, java.scripting, java.security.jgss, java.security.sasl, java.sql, java.transaction.xa, java.sql.rowset, java.xml.crypto, jdk.internal.jvmstat, jdk.management.agent, jdk.jdwp.agent, jdk.internal.ed, jdk.internal.le, jdk.internal.opt]

任何人都可以对正在发生的事情给出一些提示吗？

Answer 1

好的，所以一天的简短谷歌搜索发现:

众所周知，Kotlin 不会在生成的 jar 中包含反射实现，这不是“默认”，而是“根本”，即“绝不”。

同时java -jar omg.jar使 java 自动忽略每个类路径设置，也许保存 list 上指定的那些(我无法工作)，因为......好吧，这就是原因。

构建和运行的真正管道实际上应该读取

kotlinc -d omg.jar -include-runtime omg.kt
java -cp omg.jar:/snap/kotlin/current/lib/* OmgKt

在哪里 OmgKt是您应该猜到的主要可执行类名称。在简单的情况下，比如这个，它显然是从源文件名派生的，如果你解压缩并查看 jar 文件的内容，它可能可以找到……不知何故，当我第一次开始时它不起作用试过了。
(而 /snap/kotlin/current 表示典型的 kotlin 安装路径。)