There is a service which uses Spring AsyncRestTemplate for sending rest calls. Each call of AsyncRestTemplate.exchange() returns ListenableFuture. Something like this:
ListenableFuture future1 = new AsyncRestTemplate().exchange(...);
ListenableFuture future2 = new AsyncRestTemplate().exchange(...);
ListenableFuture future3 = new AsyncRestTemplate().exchange(...);
Is there a way for create single ListenableFuture which combines all other calls? Something like Futures.allAsList from Guava.
2 Answers
Step #1: Convert each ListenableFuture to CompletableFuture
public CompletableFuture<T> toCompletableFuture(ListenableFuture<ResponseEntity<String>> listenableFuture) {
final CompletableFuture<T> completableFuture = new CompletableFuture<>();
listenableFuture.addCallback(new ListenableFutureCallback<ResponseEntity<String>>() {
@Override
public void onFailure(Throwable e) {
completableFuture.completeExceptionally(e);
}
}
@Override
public void onSuccess(ResponseEntity<String> result) {
completableFuture.complete(parseResponse(result));
}
}
});
return completableFuture;
}
Step #2: call CompletableFuture.allOf(cF1, cF2, cF3...)
Since Spring 5.0, ListenableFuture implements the method completable() which does exactly what you need:
/**
* Expose this {@link ListenableFuture} as a JDK {@link CompletableFuture}.
* @since 5.0
*/
default CompletableFuture<T> completable() {
