```@Bean suspend fun myConvertedJavaConsumer = Con...

# server

[Alex Schiff]

@Bean
suspend fun myConvertedJavaConsumer = Consumer<String> {
  mySuspendFunction(it)
}

The above code is giving me an error, Suspension functions can be called only within coroutine body. I am trying to convert a Java consumer to a Kotlin coroutine and I'm unsure how to proceed. This is using spring-cloud-stream and spring-cloud-funciton-kotlin libraries

[ross_a]

You can't call a suspending function inside an implementation of java.util.function.Consumer as Consumer.accept isn't itself suspending

[ross_a]

If you're using some library which you pass a Consumer as a callback which is called once, you can use suspendCoroutine

If the consumer is to be called more than once, use callbackFlow

[ross_a]

class Library {
        fun attachCallback(consumer: Consumer<String>) {
            consumer.accept("hey")
        }

        fun attachListener(consumer: Consumer<String>) {
            consumer.accept("hey")
            consumer.accept("hola")
        }
        
        fun removeListener(consumer: Consumer<String>) {
            TODO()
        }
    }

    fun thing() = runBlocking {
        lateinit var library: Library

        val result = suspendCoroutine { continuation ->
            library.attachCallback { continuation.resume(it) }
        }

        val results = callbackFlow { 
            val consumer: (t: String) -> Unit = { trySendBlocking(it) }
            library.attachListener(consumer)
            awaitClose { library.removeListener(consumer) }
        }.toList()
    }

[Alex Schiff]

I got it to compile by first translating it to a Kotlin lambda (supported by the spring-cloud-function-kotlin library) then wrapping it in a coroutineScope.launch. not sure if this is the best approach or not

[ross_a]

it's fine if you are happy changing to the thread of the scope's dispatcher, else you could also do

Consumer<String> {
  runBlocking {
    mySuspendFunction(it)
  }
}

which will block on the original thread

[ross_a]

Looking at git (I've not used spring-cloud-funciton-kotlin ) it looks like suspending functions may be natively supported. Perhaps try:

@Bean
fun myConvertedJavaConsumer(): suspend (String) -> Unit {
  mySuspendFunction(it)
}

[ross_a]

https://github.com/spring-cloud/spring-cloud-function/commit/a70564eb82910691e79d50246402e6997554d9c1#diff-48ae8a004443c672[…]cb697e60da9b58c78e0R29

[Alex Schiff]

Thanks!!!