Hello. As I've previously explained, I'm developing a game and am using OSGi as the foundation. We want to encourage third-party additions to the game and are therefore publishing APIs and building the whole thing as a plugin/service-based architecture from the beginning.
Some plugin bundles will contain executable code, but others may not
contain any. Examples of bundles that probably won't contain code
are bundles containing game data such as sets of audio files, sets
of graphics files, level data, etc. Regardless of whether or not a
bundle contains executable code, I want it to be able to participate in
all of the things that make OSGi great: Proper versioning, dynamic
loading/unloading, and so on. It's not clear to me how I can achieve
this though; it seems like I'd need each bundle to unconditionally
include some compiled code, the only purpose of which is to provide
something that can register itself as a service in order to participate
in something like the whiteboard pattern.
Consider something like an audio "theme" for a user interface. The game
might define an API like:
interface SoundThemeType
{
AudioStream buttonClicked();
AudioStream scrollUp();
AudioStream scrollDown();
AudioStream alert();
}
A bundle that provided a set of sounds comprising a new theme for the
user interface would then have to provide an implementation like:
@Component
public final class ExampleSoundTheme implements SoundThemeType
{
public AudioStream buttonClicked()
{
// Return an audio stream from the bundle's own resources...
}
...
}
No doubt the actual implementation of the ExampleSoundTheme type could
be pushed up into an abstract superclass and provided by the game
itself, so the implementation in the bundle would end up being
something trivial like:
@Component
public final class ExampleSoundTheme extends AbstractSoundTheme
{
public AudioStream buttonClicked()
{
return super.sound("/button_clicked.wav");
}
...
}
However, as trivial as the above could be, it still requires an editing
tool to compile some Java code and include it into a bundle. This means
that non-technical users that just want to make a simple sound theme
have to be exposed to code (even if just indirectly). It would be much
nicer if those users could simply create a file, let's call it
"theme.txt" that looked something like:
buttonClicked: /button_clicked.wav
scrollUp: /scroll_up.wav
scrollDown: /scroll_down.wav
alert: /boom.wav
... and the editing tool would insert information in the OSGi manifest
that would, when the bundle is loaded into the game, result in an
implementation of the SoundThemeType API being created and registered
as a service using the given theme.txt file as a data source. To
reiterate: The bundle just contains theme.txt, a few .wav files, and
obviously an OSGi manifest. No compiled code.
Is there some way I can achieve this pleasantly?
M
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