Convert List<CompletableFuture> to CompletableFuture<List>

Sometimes I find myself in the situation where I have to perform some asynchronous tasks and perform another asynchronous task when all those tasks have been completed. As always in such situations, I’ve searched stackoverflow for a how-to and the top rated answer suggests the following solution:

That solution totally works and it is good. However, if you often deal with Streams, a more functional approach would be neat. So I started coding a Collector that does this operation for me in one go. I won’t go into detail of how a Collector works, but this blog-post helped me out a lot understanding it.

Finally I ended up with this solution, which I’ve uploaded to github:

And here is how you would use it:

Happy coding!


Obviously it was late yesterday ^^ The solution I posted was hidden in another answer with less upvotes. It suggest using Collectors.collectAndThen together with the sequence-method above. In my opinion this is cleaner than following my approach with writing the Collector on your own (DRY-principle). The final solution is posted below and it contains another Collector-factory method that can be used if you’re not interested in the results or the CompletableFutures to collect are of type Void.


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