title: Transform Java Future into a CompletableFuture
body: <p>Java 8 introduces <code>CompletableFuture</code>, a new implementation of Future that is composable (includes a bunch of thenXxx methods). I'd like to use this exclusively, but many of the libraries I want to use return only non-composable <code>Future</code> instances.</p>
  
  <p>Is there a way to wrap up a returned <code>Future</code> instances inside of a <code>CompleteableFuture</code> so that I can compose it?</p>