[Hawkular-dev] generation of message POJOs via JSON schema

[John Mazzitelli]

There is this really nice maven plugin that takes JSON schema and generates Java POJOs annotated with GSON annotations. I took this stuff and created a sample module in the bus repo and see how it works. It works very nicely and I think we can use this very easily in our stuff.

First, here is a site that discusses JSON schema if you aren't familiar (its essentially like XML Schema only for JSON):

http://json-schema.org/documentation.html

We can use this maven plugin to generate an API that our Java components can use to talk to each other. To see what the generated code looks like with any JSON schema, here's a play area where you can see it in realtime:

http://www.jsonschema2pojo.org/

Here's what my sample JSON schema looks like (you'll see it uses primitives as well as sets/lists and embedded types (see address type) and a set of embedded types (see phoneNumbers):

https://github.com/hawkular/hawkular-bus/blob/master/hawkular-bus-samples/hawkular-bus-sample-jsonschema/src/main/resources/schema/Person.jsonschema

Here is where my test code creates the message via the POJO API that was generated by the maven plugin:

https://github.com/hawkular/hawkular-bus/blob/master/hawkular-bus-samples/hawkular-bus-sample-jsonschema/src/main/java/org/hawkular/bus/sample/client/Main.java#L84

If we use this stuff, we write the JSON schema which automatically provides documentation that non-Java clients can use to know what the clients need to send/consume, or they can use the schema themselves to generate their own client code. We use the schema internally to generate Java POJOs that we then use in our Java components (like what my sample code demonstrates).

Here is what the maven plugin usage looks like - its pretty simple:

https://github.com/hawkular/hawkular-bus/blob/master/hawkular-bus-samples/hawkular-bus-sample-jsonschema/pom.xml#L48