A little bit of Spring and MQTT

I’ve been involved with Spring (the Java framework, not the season…) for a couple of years now – since I joined VMware in 2012 through the former SpringSource organisation in the UK – and I’ve remained “involved” with it through my transition to Pivotal and the framework’s evolution into Spring 4 / Spring.IO under Pivotal’s stewardship.

To be clear, although I’ve been a “Java guy” / hacker through my time at IBM, I have never been a hardcore JEE coder, and my knowledge of Spring itself has always been limited. My good buddy Josh (MISTER Spring, no less) has done his best to encourage me, I briefly played with Spring Shell last year with @pidster, and the brilliant work done by the Spring Boot guys has been helpful in making me look at Spring again (I spoke about Boot – very briefly, as a newcomer to it – at the London Java Community unconference back in November).

Taking all of that on board, then, I’m still an absolute Spring n00b. I recognise a lot of the benefits, I see the amazing work that has gone into Spring 4, and I’m excited by the message and mission of the folks behind the framework. I would say that though… wouldn’t I? 🙂

[considering this is my first blog post in a while, I’m taking a while to get past the preamble…]

This week, I chose to flex my coding muscles (!) with a quick diversion into Spring Integration. With a long history in WebSphere Integration back in my IBM days, this was both something of return to my roots, and also a learning experience!

With the new Spring.IO website (written with Spring, and hosted on Pivotal Web Services Cloud Foundry, fact fans!), the Spring team introduced the new Spring Guides – simple and easy-to-consume starter guides to the different technologies available in the Spring family. I knew that the team had added MQTT support via Eclipse Paho, so I thought I’d take a look at how I could modify a Spring Integration flow to take advantage of MQTT.

Incidentally, there’s complete reference documentation on the MQTT support, which is helpful if you’re already familiar with how Spring Integration works.

The resulting simple project is on Github.

Once I’d figured out that it is useful to ensure the latest versions of the various modules are listed as dependencies in the build.gradle file, it wasn’t too hard to adapt the Guide sample. In the example, the docs lead a developer through creating a new flow which searches Twitter and then passes tweets through a transformer (simply flattening the tweet sender and body into a single line of text), into an outbound file adapter.

The bulk of the changes I made were in the integration.xml file. I wanted to replace the file output with the tweets being published to an MQTT topic. To do that, I added the int-mqtt XML namespace information to the file, and configured an outbound-channel-adapter. It was also necessary to add a clientFactory bean configuration for a Paho MQTT connection. You’ll notice that, by default, my example posts results to the test broker at Eclipse (iot.eclipse.org port 1883 – an instance of mosquitto for public testing). Full information on how to build and test the simple example can be found in the project README file.

Thanks to my colleague Gary Russell for helping me to figure out a couple of things, as I was a Spring Integration newcomer!