Unhandled Promise Rejection (ARCH4031)

Key java.async.missing-future-exceptionally · Severity warning · Category async

When a future chain is left without a rejection handler (exceptionally/handle), a thrown exception becomes an unhandled rejection that is silently swallowed.

Incorrect

fetchUser(id)
    .thenApply(this::render)
    .thenAccept(this::send);   // no rejection handler

Correct

fetchUser(id)
    .thenApply(this::render)
    .thenAccept(this::send)
    .exceptionally(ex -> {
        log.error("failed to process user", ex);
        return null;
    });

Fix

Attach an exceptionally or handle stage to the future chain to log or compensate for rejections.