Transform Java Future into a CompletableFuture

Question

Java 8 introduces CompletableFuture, a new implementation of Future that is composable (includes a bunch of thenXxx methods). I\'d like to use this exclusively,

Answer 1

If your Future is the result of a call to an ExecutorService method (e.g. submit()), the easiest would be to use the CompletableFuture.runAsync(Runnable, Executor) method instead.

From

Runnbale myTask = ... ;
Future future = myExecutor.submit(myTask);

to

Runnbale myTask = ... ;
CompletableFuture future = CompletableFuture.runAsync(myTask, myExecutor);

The CompletableFuture is then created "natively".

EDIT: Pursuing comments by @SamMefford corrected by @MartinAndersson, if you want to pass a Callable, you need to call supplyAsync(), converting the Callable into a Supplier, e.g. with:

CompletableFuture.supplyAsync(() -> {
    try { return myCallable.call(); }
    catch (Exception ex) { throw new RuntimeException(ex); } // Or return default value
}, myExecutor);

Because T Callable.call() throws Exception; throws an exception and T Supplier.get(); doesn't, you have to catch the exception so prototypes are compatible.