How to attach uncaught exception handler/completion to CompletableFuture chain

Question

The use-case :

• an exception occurs during CompletableFuture chain
• none of exceptionally , whenComplete or handle method is attached to that CompletableFuture chain

The result : The exception is never caught and there's no tracking/log of it. Which in case of Async systems is 1) undesirable and 2) an indicator for hard and hidden problems (such as NPE, Runtime Exc, etc.) to spot.

The question : Is it feasible to implement CompletableFuture.UncaughtExceptionHandler mechanism by analogy / in a similar manner with java.lang. Thread.UncaughtExceptionHandler ? The idea is to provide [default] uncaught exception handler/completion to be called if the CompletableFuture chain does not have java.util.concurrent.CompletableFuture.UniExceptionally Completion attached.

Answer 1

The simple answer is: no.

However, someone posted an ugly hack to get similar behavior in another thread: How to handle uncaught exceptions from CompletableFuture.runAsync

I for one escape this problem by using ReactiveX ( http://reactivex.io ), but that choice might be beyond your control. In that case, you could consider creating a wrapped class for CompletableFuture that always registers an exception handler behind the scenes, so you don't have to explicitely call exceptionally(..) any more. But again, this is just a work-around.