JDK7/8 features in Kotlin 1.0

JDK7/8 features in Kotlin 1.0

Ilya Gorbunov

Currently it's rather inconvenient to use those methods of mapped builtin types, that were added in JDK8. These include Collection.stream(), Map.getOrDefault(K, V), etc. We have several long-standing issues related in our tracker: KT-9194, KT-5175 and KT-10864.

This happens because Kotlin targets JDK 1.6 as the minimum JDK version, so it can't expose those members of builtin types that are not available in JDK 1.6. We plan to remove the limitation in Kotlin 1.1 by exposing all builtin type members available in the target platform (excluding some blacklisted exceptions), but as a short-term fix we could provide a way to call these methods via extensions.

We have collected those extensions in a small Kotlin library: kotlinx.support. It consists of two artifacts: kotlinx-support-jdk8 and kotlinx-support-jdk7. The former has a dependency on the latter, so if you target JDK8 you could only reference kotlinx-support-jdk8 and have the latter as a transitive dependency.

These artifacts are available for downloading from the maven repository on bintray https://bintray.com/kotlin/kotlinx.support/kotlinx.support and also on jcenter https://bintray.com/bintray/jcenter?filterByPkgName=kotlinx.support.


This library provides extensions to call default methods of collection interfaces introduced in JDK8.

import kotlinx.support.jdk8.collections.*
import kotlinx.support.jdk8.text.*

// some quite more verbose way to say 'listOf<String>().flatMap { it.asIterable() }'
val chars = listOf("abc", "def").stream()
                .flatMap { it.chars().boxed().map { it.toChar() } }


This library exposes Throwable methods to work with suppressed exceptions, and introduces long-awaited use extension for AutoCloseable. Note that this use being imported explicitly has precedence over use from Standard Library and thus can be used for Closeable as well.

import kotlinx.support.jdk7.use

class Resource(val faultyClose: Boolean = false) : Closeable {

    override fun close() {
        if (faultyClose)
            throw IOException("Close failed")

// the IOException thrown by 'close' would be added
// to the list of suppressed exceptions of IllegalStateException
// thrown from lambda passed to 'use'
val result = Resource(faultyClose = true).use {
    throw IllegalStateException("operation failed")