为什么Kotlin字节码引用java.util.function.BiConsumer？

Question

从我的理解科特林应该能够使用JRE 6运行,但这个代码用foreach在地图上失败,因为对一个Java类8引用(java/util/function/BiConsumer)

CompilerTest.kt:

fun main(args: Array<String>) {
  val aMap = mapOf("bar" to "bat")
  aMap.forEach { k, v -> println("$k -> $v")}
}

编译Kotlin代码:

» kotlinc CompilerTest.kt -jvm-target 1.6 -include-runtime -d compilerTest.jar

在JRE 6上测试已编译的代码:

» docker run --rm -v "$PWD":/usr/src/myapp -w /usr/src/myapp openjdk:6-jdk-slim java -jar compilerTest.jar
Exception in thread "main" java.lang.NoClassDefFoundError: java/util/function/BiConsumer
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:643)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
    at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
    at CompilerTestKt.main(CompilerTest.kt:5)
Caused by: java.lang.ClassNotFoundException: java.util.function.BiConsumer
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
    ... 12 more

版本信息:

» kotlinc -version         
info: kotlinc-jvm 1.1.4-3 (JRE 1.8.0_131-b11)

Answer 1

原来kotlin Map继承自java.util.Map.当您调用时aMap.forEach { k, v -> println("$k -> $v")},您正在调用该方法的Java版本.

但是,如果您更改代码以获取条目:aMap.forEach { entry -> println("$entry.key -> $entry.value")},则调用Kotlin版本,代码将在JRE6上运行.

您可以通过使用编译-no-jdk器的标志进行编译来标记对JRE的依赖性.

» kotlinc CompilerTest.kt -no-jdk -jvm-target 1.6 -include-runtime -d compilerTest.jar
CompilerTest.kt:5:10: error: type inference failed: inline fun <K, V> Map<out K, V>.forEach(action: (Map.Entry<K, V>) -> Unit): Unit
cannot be applied to
receiver: Map<String, String>  arguments: ((Map.Entry<String, String>, ???) -> Unit)

    aMap.forEach { k, v -> println("$k -> $v")}
         ^
...

Answer 2

尝试禁用即时运行

Preferences > Build, Execution, Deployment

这是唯一对我有用的东西!