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From Dennis Reedy <dennis.re...@gmail.com>
Subject Re: Need for jsk-dl.jar
Date Wed, 05 Jan 2011 18:35:08 GMT

On Jan 5, 2011, at 342AM, Dan Creswell wrote:
>> 
>> 
>> Key to the modularization was to remove reliance on classdepandjar. I see
>> this as a positive, I'm not sure sure others do. IMO, it really simplifies
>> the project to not rely on classdepandjar, and have modules that produce a
>> single jar. If you all feel very strongly about having classdepandjar AND a
>> modularized project, I still doable, it will just take more work to put
>> classdepandjar back into the mix.
>> 
>> 
> Well, I'm no fan of classdepandjar but removing it is build hassle for me.
> Hassle is no big deal so long as I have a clear path forward. What can you
> do in terms of putting together an example or doc that shows how the
> "typical" Jini service would be built from now on (not sure Blitz is typical
> but there you go)?

The approach I'd give to a developer that is starting a project that will result in a River
service is a little different from taking an existing well established & thought out technology
such as Blitz. With Blitz, we're looking at a refactoring. So with that in mind I thought
I'd give myself an hour, and grabbed the Blitz source and took an hour to 'modularize' it.
After looking at the distribution I decided to break out the project into the following modules,
with each module producing a single jar, with inter-project dependencies

blitz-\
       | - blitz-stats
       | - blitz-proxy
       | - blitz-service
       | - blitz-ui

The relationship between the modules was planned to be as follows:

blitz-proxy depends on blitz-stats
blitz-service depends on blitz-proxy
blitz-ui depends on blitz-proxy

(There are other transitive deps including Jini and Sleepycat across the stack but I will
only mention those as a ref for now)

I added gradle build scripts and was making progress but ran into issues with the blitz-stats
module (containing org.dancres.blitz.stats classes), because by itself that package has deps
on other Blitz classes, including SpaceImpl, Lifecycle, LifecycleRegistry, Logging, ConfigurationFactory
(etc...), and I didnt want to bring all of this into blitz-stats, since blitz-proxy depends
on it. So, since I gave myself an hour and simply didnt know (well kinda knew) if the decisions
I would make would break everything, so I stopped. If you'd like maybe we can talk about this
offline, be glad to share what I did if interested.

So much for that experiment. However ...

The general approach is to organize a 'service' project as a multi-module project, with each
module representing  the basic architectural element of a distributed service. Breaking this
down we have the service's API, the service's proxy and the service's implementation (referenced
doc http://www.rio-project.org/conventions.html)

Given a service project with the name of hello, the service project is composed of the following
modules:

• hello-api
The hello-api module contains all the classes (interfaces and other classes) that is needed
to communicate with the service

• hello-proxy
The hello-proxy module (optional), depends on the hello-api module, and provides smart proxy
support

• hello-service
The hello-service module, depends on the hello-api module (or hello-proxy module if used)
provides the backend service implementation.

• hello-rule
The hello-rule module (optional), depends on the hello-api module and provides support for
rules associated with the service.

• hello-ui
The hello-ui module (optional), depends on the hello-api module and provides support for a
service user interface.

What I have found is I give greater thought as to what needs to go where, and what the consequences
are to adding classes (and that class's dependencies (and transitive dependencies)) to a module.
With the multi-module structure we can focus on the creation of services as a tuple of api,
proxy and implementation. I find it more constructive to have the components broken out that
produce one jar, write test cases for each module, and then write integration test cases that
incorporate all aspects of the service working together.

In addition, the products of the rproject are easier understood from a user's point of view.
They follow a convention. For example, its easy to answer the question of what jar to include
if I want to use a service, you would use (from above) hello-api-<version>.jar.

Note that the structure (approach) has been used with Maven, but as previously pointed out
Gradle is also a very (very) good candidate. Gradle itself uses Ivy for dependency resolution,
but the important thing is you can deploy your service artifacts to a Maven repository where
they can be easily included by other service developers for use. 

I would like to think that we can take this approach to modularize River. FWIW, I think River
is an 'easier' candidate than Blitz, and for what thats worth for my own project Rio [1].
River's codebase is already organized in such a way that is amenable to this model. The service
packages are all fairly self contained, they have deps to classes found in the platform and
into the application developers toolkit (jsk-lib). 

Regards

Dennis

[1]  Rio is also built using classdepandjar, and I am going to be doing this sort of refactoring
for Rio over the next few months.
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