How to send POST request asyncly?

[huasiy]

I want to use this project to send requests asyncly. But I always find respons's status code is 500. Here is my client's code:

ByteBuffer bufferCopy = ByteBuffer.wrap(Arrays.copyOf(this.buffer, this.bufferPosition));
Request req = httpClient.preparePost(this.uri)
        .setBody(bufferCopy)
        .addHeader(HttpHeaderNames.CONTENT_TYPE, "application/x-protobuf")
        .addHeader(HttpHeaderNames.CONTENT_LENGTH, String.valueOf(this.bufferPosition))
        .build();

int retry = 0;
while (true) {
    try {
        ListenableFuture<Response> future = httpClient.executeRequest(req);
        counter.incrementAndGet();
        future.addListener(() -> {
            try {
                Response response = future.get();
                if (response.getStatusCode() != 200) {
                    logger.error("Request failed: " + response.getStatusCode());
                }
            } catch (Exception e) {
                logger.error("Async request fail: " + e.getCause());
            } finally {
                counter.decrementAndGet();
            }
        }, this.executorService);

        this.bufferPosition = 0;
        break;
    } catch (Exception e) {
        retry++;
        if (retry > MAX_RETRIES || !(e.getCause() instanceof java.net.ConnectException)) {
            logger.error("retry count {}, exception cause {}, excepetion {}", retry, e.getCause(), e.getMessage());
            throw new IOException("Connect to stream failed");
        } else {
            try {
                Thread.sleep(RETRY_DELAY_MS);
            } catch (InterruptedException e1) {
                throw new IOException(e1);
            }
        }
    }
}
this.bufferPosition = 0;

Is there any error with my client code? Should I paste my http server code too?