java 8 parallel stream, blockingcode possible?

Question

My situation is quite simple.

I have a list I want to perform logic on each item asynchronically.

when all the threads are done, i want to call a close conne

Answer 1

An operation on a ParallelStream is still blocking and will wait for all the threads it spawned to finish. These threads are executed asynchronously (they don't wait for a previous one to finish), but that doesn't mean your whole code starts behaving asynchronously !

If you're actually making asynchronous calls and working on the resulting CompletableFuture in your forEach, you should instead make your terminal operation a reduce producing a single CompletableFuture. Intermediate operations could be a peek or an identity map with side-effects (both are frowned upon, but I don't know any best-practice solution). You would close the connection upon resolve of the single resulting CompletableFuture.

If you're not, then your code looks good enough, as the closeClientConnection() will only be executed once the ParallelStream has been processed.