Hey Richard.
Sorry...didn't mean to put anyone on the defensive. My point really
was around using core OSGi interfaces versus Felix iPOJO "stuff" - and
that notion. I should also apologize because I'm familiar with Brad's
work. But, noting specification (OSGi) versus standard probably is
worthy too.
The real concern is being tied to Felix, rather than just OSGi,
nothing more.
Kit
On Oct 28, 2008, at 9:43 AM, Richard S. Hall wrote:
Kit,
I would be interested in the issues that concern you. I believe it
should be possible to create components in iPOJO that use basic DoI
techniques that would travel well. Clearly, you can use more
advanced features that won't, but no one forces you to do that.
I am not really sure what "standardness" has to do with the point,
since I am not really aware of a standard in this area, unless you
are talking about DS or the Spring-DM work within the OSGi Alliance.
If so, I would say that there is nothing special about being run
through the OSGi Alliance spec process, other than getting more
feedback.
-> richard
Kit Plummer wrote:
Brad,
I would warn against the non-standard nature of iPojo. Not to say
that it is a bad thing, but given the landscape and "components" I
think you'll struggle with different issues moving in that
direction. Sure, you may resolve component dependencies -
cleaner. But, the risk is that your component no longer travels
well.
Kit
On Oct 28, 2008, at 8:04 AM, Brad Cox wrote:
I'm totally new to iPOJO but have been pusing components forever.
But I'm guessing this fine- vs coarse-grained distinction is
precisely the problem I've been struggling with org.jdom, with
lots of hand-on help from P. Kriens. So far its defeated both of us.
It seems JDOM is what you called a coarse-grained component,
developed long before this fine-grained ipojo stuff was around.
Deeply entangled with even lower-level dependencies, like Xerces.
So I've started looking at iPOJO to see whether that might be a
way forward.
I'm hoping to find a way to include jdom+dependencies in one of my
ipojos so other ipojos can resolve it from there. Seems
straightforward on the surface, if I can avoid whatever is
breaking bnd now.
Clement Escoffier wrote:
Hi,
That’s an interesting question. I would say that it slightly
depend of your use case. However, in one level of abstraction,
being consistent sounds reasonable. To illustrate this, I’m
going to describe two different types of projects choosing the
different strategies: a universe of fine-grain components, and a
universe of coarse-grain components (using regular object
collaborators).
In a project aiming to design and implement a residential
gateway, the granularity of components is rather fine-grain. The
most part of the functionalities are implemented inside
components and are available through services, such as devices,
technical services, and internal application services. For this
latter case, using iPOJO composite was crucial to maintain the
isolation of internal services that must not be accessible
outside the application (by peer that are not a part of the
application). This granularity was chosen because of the required
flexibility for runtime evolution (application updates,
modifications of the environment…). In this use case,
“everything was dynamic”.
In the Jonas JEE server, the chosen granularity was coarse-grain
(Guillaume or/and Francois, correct me if I’m wrong). Each
technical services provided by the JEE server is implemented by
iPOJO components and provided as OSGi services. Two aspects
motivated this choice. First, the Jonas team wanted to reuse the
most part of their code (makes sense right?). Then, the unit of
evolution (update) is the technical service (coarse-grain). So,
in conclusion, it’s an open question ☺. There is no generic
answer. iPOJO does not influence one or another way, because IMHO
it depends of the use case. The goal of iPOJO was to provide
functionalities to handle both cases.
Regards,
Clement
-----Original Message-----
From: Todor Boev [mailto:[EMAIL PROTECTED] Sent: lundi 27
octobre 2008 19:03
To: [email protected]
Subject: IPojo - universe of components?
Hello,
I was wondering what is iPojo's mission in life: just to make it
a bit easier to code in OSGi or the grand idea to lift the Java
language to a higher abstraction. This philosophical question is
important to me because iPojo like most other DI frameworks seems
highly viral.
For example suppose I start out with a single component class
that creates all it's collaborators with POJN (Plain Old Java
New :). At this point I will have to inject all service
dependencies into this uber-component and have it pass them on to
the constructors of it's collaborators. Soon I get sick of my
bad style and decide to let iPojo manage the collaborators and
pass around the dependencies for me. And as soon as the
collaborators are under iPojo's wing all classes that need them
will also have to be iPojo managed. And so in no time almost all
my classes will be components. All that will be left are light-
weight data objects and static utilities. The former could soon
acquire behavior of their own and will inevitably become
components because they will likely need to collaborate with
other components. As for the static utilities: unless they are
bundles of stand-alone purely functional methods they are a bad
style to begin with and should be re-cast as singleton
components. So if I go with the flow I should have a universe of
components.
Is this the way to work with iPojo? Or should restrict iPojo to
only the core graph of long-lived objects that form the basis of
my program and manage the construction, and lifecycle of the more
volatile object generations by hand?
Cheers,
Todor
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