CompletableFuture<T> freezes UI - kotlin

Question

I am currently working on an api for my client application which needs to process http requests (using unirest) asynchronously as of now. I am new to CompletableFuture and haven't worked with anything similar up to this point. I was wondering whether the following structure makes sense:
// Request.kt (simplified)
class Request<T>(
// other variables relevant to the request such as body or path ...
private val responseType: Class<T>
) {
fun prepareRequest(action: (HttpRequest<*>) -> U): U {
// preprocesses the request, adds body if necessary and returns the request itself
}
fun executeAsync(action: (HttpResponse<T>) -> Unit) {
prepareRequest { req ->
action(req.asObjectAsync(responseType).get()) // Unirest call that (still) freezes the UI
}
}
// Builder logic ...
}
// ApiClient.kt (simplified)
abstract class ApiClient {
protected fun <T> executeAsync(req: Request<T>, action: (T) -> Unit) {
req.executeAsync { res ->
if (res.isSuccess){
action(res.body)
} else {
throw RuntimeException("res != 200")
}
}
}
}
// AuthClient.kt (simplified)
class AuthClient : ApiClient() {
fun signin(email: String, password: String, onSuccess: () -> Unit) {
executeAsync(
Request.builder(TokenModel::class.java)
.post("/signin")
.body(SignInModel(email, password))
.build()
) {
onSuccess() // this is going to refresh the UI, once the http request has been executed
}
}
}
As the call to get on CompletableFuture freezes the UI I thought of including an Executor or a Thread instead so that executeAsync in Request becomes the following:
fun executeAsync(action: (HttpResponse<T>) -> Unit) {
prepareRequest { req ->
Executors.newSingleThreadScheduledExecutor().execute {
action(it.asObjectAsync(responseType).get())
}
}
}
Is my structure overly complex or does it have to be like that? Do I need the Thread/Executor or can this be achieved in a different way?