Vert.x Java 列表<Futures>参数化

Question

I ran in to a strange issue with Vert.x futures the other day that doesn't break the code but bothers me still.

Future without parameter results in the following warning:

Future is a raw type. References to generic type Future should be parameterized

Add the parameter, problem solved:

Future<YourClassName> future = ...

When dealing with a list of futures, you can also parameterize it just fine:

List<Future<YourClassName>> future = ...

But CompositeFuture.all() can't seem to deal with a parameterized list and forces you to remove the parameter.

Is there any way to make parameterized list of futures work with CompositeFuture or do we just have to ignore that warning? It doesn't break anything but would still be nice to find a solution to get rid of that warning.

Answer 1

On one hand, you can't use CompositeFuture.all() with list of parametrized futures. This is a design decision that the developers took, due to type erasure.
But actually, CompositeFuture.all() doesn't do anything special. So you may have your own interface with static method, that will do the same:

interface MyCompositeFuture extends CompositeFuture {

    // This is what the regular does, just for example
    /*
    static CompositeFuture all(List<Future> futures) {
        return CompositeFutureImpl.all(futures.toArray(new Future[futures.size()]));
    }
    */

    static <T> CompositeFuture all(List<Future<T>> futures) {
        return CompositeFutureImpl.all(futures.toArray(new Future[futures.size()]));
    }
}

And now:

    List<Future<String>> listFuturesT = new ArrayList<>();
    // This works
    MyCompositeFuture.all(listFuturesT);

    List<Future> listFutures = new ArrayList<>();
    // This doesnt, and that's the reason for initial design decision
    MyCompositeFuture.all(listFutures);

Answer 2

CompositeFuture.all() returns a CompositeFuture , which is itself a Future<CompositeFuture> . So you can assign the result to a Future<CompositeFuture> instead of a raw Future :

Future<String> fut1 = asyncOp1();
Future<Integer> fut2 = asyncOp2();
Future<CompositeFuture> all = CompositeFuture.all(fut1, fut2);

Answer 3

[promoting a comment]

Suggestion from @ oh-god-spiders in the comments did help in my case.

val futures: util.List[Future[List[CustomClass]]] = asyncCode()
// Doesn’t work
val compositeFuture = CompositeFuture.all(futures)

// Works
val compositeFuture = CompositeFuture.all(new util.ArrayList[Future[_]](futures))