在Kotlin中实现onComplete Scala Future

Question

我正在从Kotlin调用一个Scala类，该类返回Future，我可以对该未来进行Await

private fun scalaFutureInKotlin() {
val future: Future<String> = Future.successful("Hello world from Scala")
val result: String? = Await.result(future, Duration.apply(10, TimeUnit.SECONDS))
println(result)
}

但我真正想要的是能够实现onComplete回调，并将值传递到KotlinChannel或Flow中，以便在另一个coroutine中使用，这样我就不会阻塞任何线程。

知道如何在Kotlin中实现Scala Future的onComplete功能吗？

Answer 1

根据答案：

从Scala 2.13开始，标准库包括scala.jdk.FutureConverters，它提供Scala到Java的Future转换(反之亦然(：

import scala.jdk.javaapi.FutureConverters
import java.util.concurrent.CompletionStage
val javaFuture: CompletionStage<Int> = FutureConverters.asJava(scalaFuture)

一旦您获得CompletionStage，您就可以在Kotlin中使用以下选项进行交互：

1. 由于kotlin.coroutines提供了在其上定义的CompletionStage.await函数，因此您可以异步等待未来的完成：

// Dependencies:
// implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.9"
// implementation "org.jetbrains.kotlinx:kotlinx-coroutines-jdk8:1.3.9"
import kotlinx.coroutines.future.*
import java.util.concurrent.*
import scala.jdk.javaapi.FutureConverters
private suspend fun scalaFutureInKotlin() {
val future: Future<String> = Future.successful("Hello world from Scala")
val javaFuture: CompletionStage<Int> = FutureConverters.asJava(future)
val result: String? = javaFuture.await()  // asynchronous await, function resumes when result is available, callable by suspend function only
println(result)
}
// Examples:
suspend fun main() {
scalaFutureInKotlin()
}
// or for calling from coroutine when not inside suspendable block
fun main() {
val scope = CoroutineScope(Dispatchers.Default)
scope.launch { scalaFutureInKotlin() }  // call from inside coroutine
}

2. 直接将侦听器添加到CompletionStage：

import java.util.concurrent.*
import scala.jdk.javaapi.FutureConverters
private fun scalaFutureInKotlin() {
val future: Future<String> = Future.successful("Hello world from Scala")
val javaFuture: CompletionStage<Int> = FutureConverters.asJava(future)
javaFuture.thenAccept { result ->  // use thenApply if you want to return sth and chain the calls
println(result)
}
}