A framework for creating Alexa Smart Home Skills in Java
The Amazon Echo products, and the Alexa Smart Home interface opens up all sorts of possibilities for controlling devices around the home. Writing an Alexa skill, however, requires writing code for Amazon Lambda. Lambda provides support for a strong array popular languages including Node.js, Python, and Java, but very few examples are given to Java in terms of Smart Home Skills, and there are no canonical Java object bindings for the request/response objects that SmartHome passes to Lambda.
To complicate matters, Lambda's built-in serialization/deserialization for POJOs is of little help for the request/response objects that SmartHome makes use of, because of the dynamically-typed payload field which require special handling.
This software attempts to bridge that gap by providing a small framework to cut down on boilerplate and scaffolding for authors of Amazon Lambda functions for Alexa Smart Home Skills. It has minimal dependencies, and all business logic is left up to the user to implement, using whatever additional libraries they wish.
In short, it's tedious to write all this object serialization - I wrote all the boilerplate so you don't have to.
Lambda's execution model of completely stateless application code means that you can't assume very much about where and how things will run, how many times your code gets executed, and so on. From a scaling perspective that's appealing, but as Java service developers, that's a bit of a pain because we're so used to writing applications which can take a while to start up as long as they're quick for the rest of the time they're serving requests.
Since this is Lambda, we're constrained to either a zero-arg or default constructor for the class which implements the method that Lambda will be calling:
public final void handleRequest(InputStream inputStream, OutputStream outputStream, Context context)
This framework implements this for you in SmartHomeDirectiveHandler. Because this is the main entry point to the
code, this class is also required to have a zero-argument constructor.
Users of this framework configure their application by configuring and registering RequestHandlers for each Request
type that you expect to process. Be sure to always register a handler for the Device Discovery process. Each Handler
should provide the appropriate response; the Request objects carry the appropriate type parameters to ensure that
handlers obey this constraint.
Your implementation should extend SmartHomeDirectiveHandler and initialize and register handlers by overriding the init() method.
Compiled code is available on Maven Central.
I have used this myself in a personal project and it "works for me", as they say. I'm still working on adding more tests, and implementing object types that I didn't happen to need.
This code is in pre-1.0 state and it probably shows. I anticipate making changes, especially optimizations in the initialization phase which will probably be API-breaking.
You can find me on Twitter at @gdickinson.