如何在Kotlin中正确实现whenCompleteAsync(BiConsumer,Executor)方法

函数实现（扩展CompletableFuture） #

Kotlin可以直接基于Java的CompletableFuture实现该方法，既兼容Java的BiConsumer接口，也能用Kotlin原生函数类型简化写法：

import java.util.concurrent.CompletableFuture
import java.util.concurrent.Executor
import java.util.function.BiConsumer

// 方式1：兼容Java BiConsumer接口
fun <T> CompletableFuture<T>.whenCompleteAsync(
    action: BiConsumer<in T, in Throwable>,
    executor: Executor
): CompletableFuture<T> {
    return this.whenCompleteAsync(action, executor)
}

// 方式2：使用Kotlin函数类型更简洁
fun <T> CompletableFuture<T>.whenCompleteAsync(
    action: (T?, Throwable?) -> Unit,
    executor: Executor
): CompletableFuture<T> {
    val resultFuture = CompletableFuture<T>()
    this.whenComplete { value, throwable ->
        executor.execute {
            try {
                action(value, throwable)
                if (throwable != null) {
                    resultFuture.completeExceptionally(throwable)
                } else {
                    resultFuture.complete(value)
                }
            } catch (e: Exception) {
                resultFuture.completeExceptionally(e)
            }
        }
    }
    return resultFuture
}

调用示例 #

import java.util.concurrent.Executors

fun main() {
    val executor = Executors.newSingleThreadExecutor()
    val testFuture = CompletableFuture.supplyAsync { "Kotlin Async Test" }

    // Kotlin函数类型回调写法
    testFuture.whenCompleteAsync({ value, throwable ->
        println("异步回调结果：$value")
        throwable?.let { println("捕获异常：${it.message}") }
    }, executor)

    // Java BiConsumer风格回调写法
    val javaStyleAction = BiConsumer<String, Throwable> { value, throwable ->
        println("Java风格回调结果：$value")
    }
    testFuture.whenCompleteAsync(javaStyleAction, executor)
}

语法要点说明 #

• Kotlin中泛型的? super T对应in T（逆变），表示参数可接受T或其父类类型。
• Java的BiConsumer可直接用Kotlin lambda实现，也能替换为更简洁的Kotlin函数类型(T?, Throwable?) -> Unit。
• Executor是Java并发包接口，可通过Executors工具类创建线程池实例。

内容的提问来源于stack exchange，提问作者Mudit