8:57 a.m.
The quick summary of this email: the Hawkular Wildfly Monitor Agent will not be able to
run on WildFly 9 in its current state. It must be refactored due to changes that were made
in the WildFly 9 subsystem extension API.
Details:
After staring at this for a while, I found that our currently WildFly8 code layout of the
subsystem extensions in the agent needs to change for this to run in WF9 - I don't
think I used this approach in the bus or nest subsystem extensions so nothing needs to
change there.
The design pattern here is to use PersistentResourceDefinition subclasses for our the
subsystem resource definitions (called the Definition classes). In here you define static
members for all attributes and operations as well as an INSTANCE object of the definition
itself, among other things.
The problem is, that same Definition class needs to grab (and thus create) an instance of
the AddStepHandler within the Definition class' constructor. And THAT AddStepHandler
needs to refer back to the Definition object for the attributes. Today, it does so in the
populateModel() overloaded method, which isn't a problem. However, we needed to access
a parent class' data field (this.attributes) to set our attributes in that
populateModel() method. Unfortunately, that parent class in WF9 has changed that
this.attributes data field to final. So we can't do that anymore. Instead, it appears
the only way to set the attributes now is to pass them in via the AddStepHandler
class' constructor (calling the superclass's "super(Collection<?>
attributes")).
But this introduces an ugly circular dependency in the Definition and AddStepHandler
constructors - it bombs with an NPE.
So this means in order for us to move the agent to WF9, I would need to refactor the
subsystem definition classes - I would probably have to extract out all of the
attribute/operation definitions into some independent class that can be shared between the
*Definition and *Add classes to avoid this constructor-circularity dependency. It probably
won't be hard to do this, just a hour or two hopefully. But as it is now, it can't
run on WF9.