In that case, It's possible to have the webapp launching an OSGi gateway. You could have the core classes in the WEB-INF/lib/*.jar (or WEB-INF/classes) and have a selected set of packages (from the core) exported by the gateway (through the System Bundle). So your extensions (standard bundles) can use the packages from the core.Yes that could be done. We'd need to use the Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA config property and manually list all packages (this is a pain!).Not all packages, only the ones you want to be exported (basically your APIs). In fact, you'll choose to export the packages that you think could be used by extensions.Yes but this is still some hard work since anytime a new API is introduced we'll need to remember to update that configuration.
Yes, but in an ideal world you should not introduce new core APIs every days :)
I guess an alternative would be to create a xwiki core bundle that is empty except for Bundle-Classpath in its manifest, generated by the maven bundle plugin and pointing to WEB-INF/lib/*.jar.Hmm, not sure it will work. Bundle-Classpath refers to some inner jar file theoretically ...> From what I understand from http://www.aqute.biz/Blog/2007-02-19 it should work I think.
I'm not convinced :)I think the example Peter put on this page is what you could do if you were transforming a war into a bundle. In the case we're discussing, we're talking about having a normal webapp that launch an OSGi framework.
B) In practice it's very hard to use OSGi with only a part of the modules being OSGi bundles and another part being standard external libraries. Everything must be OSGified for it to work well.Note: I like what I saw in OSGi and I still think one goal of xwiki should be to integrate with OSGi (or with the JSR294 to be more generic, if that JSR is implemented one day... ;)). It's just that for the Extension Manager use case, I'm not sure we need OSGi from the onstart.This time, it's me that doesn't really know what will go in this ExtensionManager, and more generally, what is an Extension :) All depends of what extensions are.It's a mix of wiki pages, jars containing xwiki component implementations (like a xwiki java macro) and external jars (third party libraries). See http://dev.xwiki.org/xwiki/bin/view/Design/ExtensionManager for more details of what we'd like. Note that I need to update this page since Thomas has almost convinced me that we don't need a super XAR format and that we can keep the XAR format for wiki page as it is now and not have a single jar/zip by using a special empty artifact made only of a POM listing what an extension is (ie a list of dependencies on XARs and jars).
An extension could be seen as a bundle (containing librairies and resources), importing some packages and providing some µservices (making them available for other to use them).
If you have a small core and everything else provided as extensions, putting OSGi from the onstart may be a good choice. If extensions are java classes (that can be seen as services), using OSGi just for them also may be a good soft introduction to OSGi. If extensions are not java code, OSGi is a bad idea :)We have both (and code can be provided by wiki pages in the form of scripts and macros) but we cannot have different versions of wiki pages right now inside a single xwiki instance (I'm not talking about page history but about branches, each having its history). Another problem I mentioned would be to decide what classloader to use when executing a {{script}} macro.
If you think in OSGi terms, something that you use is probably a dependency on a µservice.
So the wiki page would be "linked"/injected to/with the "script" µservice.The difficulty here is that the dependency is actually kind of hidden in the wiki page, it's not explicit (like an @Inject field for example). It's easier when we start with a component model, because theses models are designed to explicitely declares dependencies so that a container can handle them for you.
What I have the habit to say is that : "OK, OSGi have a powerful Classloading model, but most of the time we should not touch or even think about ClassLoaders". When you look at µservices that run on top of OSGi, they're never using ClassLoaders, they always talk to other services through API.
I mean that ClassLoaders handling is the job of the OSGi framework.The consummer service will be injected with a compatible dependency service (compatible in terms of packages, so versioned) and will just call the dependency, not worrying about ClassLoading issue.
--G
Thanks -VincentThanks for the info Guillaume, -Vincent PS: I'm still discovering all this and I'm not yet 100% sure of what I say. There's a little nagging thought in the back of my head that tells me that going with OSGi now is the best thing to do even though we might not need all its power (and complexity) right now but that it would be easier to shift now than later... ;)I understand, moving to OSGi for JOnAS has been a long work (and still not completely finished to some aspects), but we started with a non modular architecture, spaghetti code, ... :'( In your case, I've understood that you have clean APIs, already have modules, so the move should be easier :) --GCheers --Guillaume4) We can easily use the Maven 3 Embedder to download and install maven artifacts into a local repository. This is convenient since we already deploy our applications/modules to a maven repository. Note that the only "difficult" part here might be searching into a remote repository; I don't know if a maven api exists for this (but probably). In the worst of cases we could use the Nexus REST API to provide this feature for now. And here's what I think we should do right now: i) focus on the 2 features we need for the Extension Manager: -- ability to install an application containing not only wiki pages but also jars -- ability to install an application from a remote repository ii) then once i) is done focus on the upgrade part of the extension manager Implementation note: - To implement i) we can do this easily I believe using a custom URL ClassLoader (we already have one btw used in the script macro) that we pass to the Component Annotation Loader when a new JAR is installed (in order to register the components in that jar) + set that custom URL ClassLoader as the new thread context classloader (for code that would use the thread context classloader to load classes). WDYT? Thanks -Vincent PS: I'd be interested to hear from OSGi experts what they have to say about this since I'm an OSGi newbie and there might be stuff I have not seen/realized. PPS: I'm just realizing that the proposal in this mail is close to Pomegranate's idea: http://www.caucho.com/projects/pomegranate/_______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
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