@Override
    public String toString() {
        T value = null;
        Throwable exception = null;
        try {
            value = completableFuture.getNow(null);
        } catch (CompletionException e) {
            exception = e.getCause();
        } catch (Exception e) {
            exception = e;
        }
        return String.format("KafkaFuture{value=%s,exception=%s,done=%b}", value, exception, exception != null || value != null);
    }
Returns true if completed in any fashion: normally, exceptionally, or via cancellation.
clients/src/main/java/org/apache/kafka/common/internals/KafkaFutureImpl.java