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<T> in your forEach, you should instead make your terminal operation a reduce producing a single CompletableFuture<T>. 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<T>.

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