Java: callback (from bungeecord) to callable.

CallbackToCallable.java

public static <V> Callable<V> createCallable(Consumer<Callback<V>> callbackConsumer) {
    return new Callable<V>() {
        private final CountDownLatch countDownLatch = new CountDownLatch(1);

        private V result;
        private Throwable error;
        public void callbackDone(V result, Throwable error) {
            this.result = result;
            this.error = error;
            countDownLatch.countDown();
        }

        @Override
        public V call() throws Exception {
            callbackConsumer.accept(this::callbackDone);
            countDownLatch.await();
            if (this.error != null) {
                throw new RuntimeException(this.error);
            }
            else {
                return this.result;
            }
        }
    };
}