using Apache's AsyncHttpClient in a storm bolt

Question

I have a bolt that is making an API call (HTTP Get) for every tuple. to avoid the need to wait for the response, I was looking to use the apache HttpAsyncClient.

after instantiating the client in the bolt's prepare method, the execute method constructs the URL from the tuple and calls sendAsyncGetRequest(url):

private void sendAsyncGetRequest(String url){

    httpclient.execute(new HttpGet(url), new FutureCallback<HttpResponse>() {

        @Override
        public void completed(HttpResponse response) {
            LOG.info("Response Code : " + response.getStatusLine());
            LOG.debug(response.toString());
        }

        @Override
        public void failed(Exception ex) {
            LOG.warn("Async http request failed!", ex);
        }

        @Override
        public void cancelled() {
            LOG.warn("Async http request canceled!");
        }
    });
}

the topology deploys but the Storm UI shows an error:

java.lang.RuntimeException: java.lang.IllegalStateException: Request cannot be executed; I/O reactor status: STOPPED at backtype.storm.utils.DisruptorQueue.consumeBatchToCursor(DisruptorQueue.java:12

Answer 1

I got this to work with no issues. the key things to note are:

1. declare the client on the bolt class scope

    public class MyRichBolt extends BaseRichBolt { private CloseableHttpAsyncClient httpclient; 

2. Instantiate and stat the client in the bolt's prepare method

    @Override public final void prepare(Map stormConf, TopologyContext context, OutputCollector collector) { try { // start the http client httpclient = HttpAsyncClients.createDefault(); httpclient.start(); // other initialization code ... } catch (Throwable exception) { // handle errors } } 

3. make the calls in the bolt's execute method

    @Override public final void execute(Tuple tuple) { // format the request url String url = ... sendAsyncGetRequest(url); } private void sendAsyncGetRequest(String url){ logger.debug("Async call to URL..."); HttpGet request = new HttpGet(url); HttpAsyncRequestProducer producer = HttpAsyncMethods.create(request); AsyncCharConsumer<HttpResponse> consumer = new AsyncCharConsumer<HttpResponse>() { HttpResponse response; @Override protected void onResponseReceived(final HttpResponse response) { this.response = response; } @Override protected void onCharReceived(final CharBuffer buf, final IOControl ioctrl) throws IOException { // Do something useful } @Override protected void releaseResources() { } @Override protected HttpResponse buildResult(final HttpContext context) { return this.response; } }; httpclient.execute(producer, consumer, new FutureCallback<HttpResponse>() { @Override public void completed(HttpResponse response) { // do something useful with the response logger.debug(response.toString()); } @Override public void failed(Exception ex) { logger.warn("!!! Async http request failed!", ex); } @Override public void cancelled() { logger.warn("Async http request canceled!"); } }); } 

Answer 2

Are you shutting down the client (client.close();) in your main flow before the callback can execute?

The error is saying that the IO path has already been closed. In general, instances of async clients should be re-used for repeated requests and destroyed only when "ALL" requests have been made, eg at application shutdown.