Call Kotlin suspend function in Java class

Question

Assume we have the following suspend function:

suspend fun doSomething(): List<MyClass> { ... } 

If I want to call this function in one of my existing Java classes (which I'm not able to convert to Kotlin for now) and get its return value I have to provide a Continuation<? super List<MyClass>> as its parameter (Obviously).

My question is, How can I implement one. Specially its getContext getter.

Answer 1

First, add org.jetbrains.kotlinx:kotlinx-coroutines-jdk8 module to your dependencies. In your Kotlin file define the following async function that corresponds to Java style of writing async APIs:

fun doSomethingAsync(): CompletableFuture<List<MyClass>> =     GlobalScope.future { doSomething() } 

Now use doSomethingAsync from Java in the same way as you are using other asynchronous APIs in the Java world.

Answer 2

If you dont want to use org.jetbrains.kotlinx:kotlinx-coroutines-jdk8, I have a new idea.

Write below code in your kotlin project.

    @JvmOverloads     fun <R> getContinuation(onFinished: BiConsumer<R?, Throwable?>, dispatcher: CoroutineDispatcher = Dispatchers.Default): Continuation<R> {         return object : Continuation<R> {             override val context: CoroutineContext                 get() = dispatcher              override fun resumeWith(result: Result<R>) {                 onFinished.accept(result.getOrNull(), result.exceptionOrNull())             }         }     } 

I write it in my Coroutines class

Then you can call your suspend function like:

            Coroutines coroutines = new Coroutines();             UserUtils.INSTANCE.login("user", "pass", coroutines.getContinuation(                     (tokenResult, throwable) -> {                         System.out.println("Coroutines finished");                         System.out.println("Result: " + tokenResult);                         System.out.println("Exception: " + throwable);                     }             )); 

login() function is a suspend function.
suspend fun login(username: String, password: String): TokenResult

For your code, you can:

doSomething(getContinuation((result, throwable) -> {         //TODO }));