Polling SQS using dropwizard

Question

What I am trying to achieve:

I want to make a dropwizard client that polls Amazon SQS. Whenever a message is found in the queue, it is processed and stored.

Some information about the processed messages will be available through an API.

Why I chose Dropwizard:

Seemed like a good choice to make a REST client. I need to have metrics, DB connections and integrate with some Java services.

What I need help with:

It is not very clear how and where the SQS polling will fit in a typical dropwizard application.
Should it be a managed resource? Or a console reporter console-reporter? Or something else.

What kind of polling do you need? At fixed interval or as long as messages are available in the queue? — Dhruvil Vaghela
– Dhruvil Vaghela, Commented Aug 31, 2018 at 8:38
I had to implement a somewhat "smart" polling (long polling + back-off strategies + message blocking). These are implementation level details for my use case though. The first answer was a good enough pointer in the right direction :) — fzn
– fzn, Commented Sep 1, 2018 at 12:30

Rishikesh Dhokare · Accepted Answer · 2018-08-30 12:04:33Z

You can use com.google.common.util.concurrent.AbstractScheduledService to create a consumer thread and add it to the dropwizard's environment lifecycle as ManagedTask. Following is the pseudocode -

public class YourSQSConsumer extends AbstractScheduledService { @Override protected void startUp() { // may be print something } @Override protected void shutDown() { // may be print something } @Override protected void runOneIteration() { // code to poll on SQS } @Override protected Scheduler scheduler() { return newFixedRateSchedule(5, 1, SECONDS); } }

In Main do this -

YourSQSConsumer consumer = new YourSQSConsumer(); Managed managedTask = new ManagedTask(consumer); environment.lifecycle().manage(managedTask);

Dhruvil Vaghela · Accepted Answer · 2018-09-01 19:25:17Z

As an alternative to RishikeshDhokare's answer, one can also go ahead with the following code which does not need to include additional jar as a dependency in your project to keep the uber jar as much lightweight as possible.

public class SQSPoller implements Managed, Runnable { private ScheduledExecutorService mainRunner; @Override public void start() throws Exception { mainRunner = Executors.newSingleThreadScheduledExecutor() mainRunner.scheduleWithFixedDelay(this, 0, 100, TimeUnit.MILLISECONDS); } @Override public void run() { // poll SQS here } @Override public void stop() throws Exception { mainRunner.shutdown(); } }

And in the run() of your Application class, you can register the above class as follows.

environment.lifecycle().manage(new SQSPoller());

You can use either scheduleWithFixedDelay() or scheduleAtFixedRate() depending upon your use case.

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