William Drew wrote:
I am looking for some guidance on best practices or well known approaches to
building OSGi “enabled” applications. Currently I have an application that
is started from the command line calling a class with a static main().
Ø java –classpath <whatever> com.mycompany.MyApplication
I’d like to take advantage of the modularity and adability of OSGi but I’m
not sure of the best way of approaching it. Do I embed an OSGi framework in
the existing application? Do I start an OSGi framework and install the
required bundles which would “start” the application? Any guidance on how to
approach this or how others are OSGi enabling their applications or systems
would be appreciated.
The best way is to split your existing code into bundles - bundelize the
app. That is also the most work :) To do this you follow the natural
modularization of the code - you must have some "design level" modules
right? With OSGi you make them explicit and call them bundles. You can
do this gradually: put all the code in one bundle and start splitting
off pieces from it into other bundles. This goes much like you would
refactor a fat class. I advise you to use iPojo or Dependency Manager to
hide the OSGi API. Using the raw API will require much more boilerplate
coding and unless you are extra careful it is very easy to introduce
dependencies to BundleContext deep into your code - that will hinder
unit testing.
When you are done you will have a configuration of N bundles placed in
directory somewhere. You start the app by simply starting the OSGi
container and pointing it to that directory (Felix works this way if im
not mistaken). The container starts the bundles. One of these bundles
contains the code that used to be in "main". When it starts it should
launch a thread that will drive the application (the thread that calls
"start()" to the bundle should not be blocked). Most of the other
bundles simply compose some services in order to produce their own
service. They do not start threads. In fact if you use iPojo you won't
have to think at all about who drives the application and all of this
threading business.
Hope this helps,
Todor
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