Spring, Reactor & Event driven programming on the JVM

Following my previous outing playing with the Spring-Boot microservices stuff, I once again found myself looking through some of the Spring libraries and came across the Reactor integration stuff.  It looked interesting, and thought I would have a quick look at the asynchronous event-driven model.

As always with Spring Boot, it was super simple to get an app up and running - it's worth noting that the app doesn't really get that much into the async processing side (or really expose scenarios with potential benefits/pitfalls of the approach) - but it gets an app up and running pretty easily.

Event streaming

Obviously, to get started I needed some kind of event source (I could have just stubbed out some code to just randomly create events in the system, but I wanted something more real). Obviously, with the modern web & big data, we have a tonne of events that we could use. I went for the obvious choice of the Twitter streaming API - as it exposes a streaming API I could just connect to that and on receipt of any tweet then just push an event on to my EventBus for any interested parties to process.

The basics of connecting to the Twitter streaming API are pretty simple using Spring-Boot and Spring-Social - I just created a simple Spring-Boot webapp that just exposed a simple page to connect to Twitter (OAuth via Spring-Social) and then on connection just connected to the streaming API and started listening.

First I just connected to the sample "firehose" stream, which is supposed to be 1% of the total twitter stream (I saw reported that there are 500million tweets a day, so you'd be looking at about 5million random tweets sent a day) - But I decided to consume the tweet events to pull out data about the current ongoing Rugby World Cup (England 2015), so I switched to the search stream limiting by references to the world cup.

The searching stream provided a reasonable number of tweets, and I think whilst I was running during the England vs Australia game I processed ~500,000 rugby related tweets.

Configuring reactor

Getting reactor up and running is really easy with Spring:

The EventBus configuration is interesting, as it has options to use different patterns including the LMAX pattern - in this case I just went with a standard thread pool approach.

The tweet-eater

To be honest, the use of reactor was overkill for this experiment, as the Spring-Social API allows you to define listeners for the streaming APIs which have a handle tweet method, much like an event consuming interface. But as it was just an experiment I continued and just used that listener to push the events on to the event bus.

As you can see above, its pretty simple - the listener just creates the event object and pushes it onto the EventBus.  So, with that done, and the basic Spring-Social connection setup to listen to the stream we will have a nice flow of events being pushed (at quite a high rate!) onto the EventBus. Now we just need something to consume those events.

Event consumers

The first consumer I created was just a very basic logging consumer - all it did was count events and then log numbers

Pretty simple

Next up,  I created a basic consumer to inspect the tweets, identify rugby teams mentioned and persist the data to Redis - this was also pretty easy, as Redis integration works pretty simply and Twitter created a set of standard team hashtags for the competition - So I just mapped those to countries, and setup my consumer to check for those

I quickly stuck some lipstick on the interface to display number of tweets per country and we were off!

Like I said, it's only barely scratching the surface of async event based programming, but it shows how easy it is to get the EventBus up and running with Spring.

As always, the code for the full app is over on GitHub - if you just clone the project and add in your own Twitter API keys in the config then you should just be able to build the JAR and run it directly.

rob hinds

I'm on to the next one, on to the next one..