Lift and OSGi

[madrenegade]

Hello all,

does anybody know what is possible with Lift and OSGi atm?

I cannot find information on that topic except for some old stuff.

I am asking because it would be really nice to have a website consisting
of several modules (which are OSGi bundles) and
dynamically adding/removing modules. This process should have the
ability to modify the sitemap and register snippets etc.
(I think dynamically adding snippets is already possible)

Thanks in advance

[David Pollak]

Lift does not support OSGi.  Sorry.

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[Donald McLean]

Also, because of conflicts, OSGi does not work well in some web containers.

That's why part of my current project contains an OSGi-like library
(written in Scala) specifically for use with Lift. Originally, it was
because I liked some of the OSGi concepts, but lately, it also turns
out that I need the ability to dynamically load and unload contexts.

Donald

[madrenegade]

On 01/16/2012 08:24 PM, David Pollak wrote:
> Lift does not support OSGi. Sorry.

That's a pity. Are there any plans to change this in the (near or far)
future?

[Guofeng Zhang]

I think it not difficult for Lift works on OSGi like Felix, Virgo or Karaf. I have done it.

(1) For complicated web application, it is good to partition it into bundle or the war will be too large (in OSGi environment).
(2) Sitemap and snippets in Lift make Lift a good web framework for dynamic web application, I means it could be like we develop plug-ins for Eclipse IDE to extend Eclispe IDE. I think this is what madrenegade want to do on Lift. Virgo has a project called Snaps which can plug in a snap to extend a web application at runtime like you extend Eclipse IDE using plugins. But Snaps couple with Tomcat. Because Lift abstract from the servlet implementation, I think Lift could do it even better and portable but it need some further work on Lift.

I have a post about how to fix Lift 2.4 for Lift work on OSGi.
https://groups.google.com/group/liftweb/browse_thread/thread/339f868df413e34b?fwc=1

You also need to solve the classloader issue for templates, CSS/js resource and properties (i18n). The following is what I defined in Boot.scala:
// ClassLoaderFactory is imported from Spring OSGi util package.
val clsLoader = ClassLoaderFactory.getBundleClassLoaderFor( Activator.INSTANCE.getBundleContext.getBundle() )

// our i18n resources
LiftRules.resourceNames = "user" :: "statistics" :: LiftRules.resourceNames
LiftRules.resourceBundleFactories.append {
case ("user", locale) => java.util.ResourceBundle.getBundle("user",locale, clsLoader )
case ("statistics", locale) => java.util.ResourceBundle.getBundle("statistics",locale, clsLoader )
}

// the classpath and context resource, which used to load js/css and template (html files)
var getResource = LiftRules.getResource ;
val getResourceFromBundleClasspath : String => Box[ java.net.URL ] = {
path =>
val bundle = Activator.INSTANCE.getBundleContext.getBundle()
Box !! bundle.getEntry( path ) or Box !! bundle.getResource( path ) or getResource ( path )
}
LiftRules.getResource = getResourceFromBundleClasspath

// lookup props/default.props
val propsPath = "/props/default.props"
val here : () => List[(String, () => Box[java.io.InputStream])] = () =>
List( (propsPath + "ui", clsLoader.getResourceAsStream( propsPath ) match {
case null => ()=>Empty
case i => ()=>Full( i ) }
) )
Props.whereToLook = here

When I did the above, I think how excellent Lift make it independent on OSGi API by its configurable design.

There are issues need to solve or research on further:
(1) How let other bundle to add the above logic in its Activator's start() method, and remove it in Activator.stop() method.
(2) How to refresh SiteMap at runtime when SiteMap is changed by a bundle (add/remove).

I'd like to discuss it with your guys if you think it is interested.

Guofeng

Donald

--

[Naftoli Gugenheim]

If you don't mind having to restart the servlet then you don't need osgi. There are other ways to do this kind of thing.
You can use traits to decouple features, and package them into various jars. Then you can use the service provider interface or JCL etc. to load jars in a known location and find classes that implement various traits. See java.sun.com/developer/technicalArticles/javase/extensible/ and https://github.com/kamranzafar/JCL/.
Another option is http://github.com/marcusatbang/Hooks.

[madrenegade]

Yeah basically mostly it is not a problem. BUT it is not possible to alter the sitemap after boot. This is the main problem!

[Naftoli Gugenheim]

That's certainly not an OSGi question.

Basically you have to:

1) Define the SiteMap to be as general as possible (for instance, access to all paths under /xxx should be subject to a testing function that is defined externally and makes use of the dynamic site structure). SiteMap will only be used for access testing, not UI.

2) Use your own data structure and snippet to display the navigation user interface.

[madrenegade]

On 01/18/2012 12:19 PM, Naftoli Gugenheim wrote:

That's certainly not an OSGi question.

Basically you have to:

1) Define the SiteMap to be as general as possible (for instance, access to all paths under /xxx should be subject to a testing function that is defined externally and makes use of the dynamic site structure). SiteMap will only be used for access testing, not UI.

2) Use your own data structure and snippet to display the navigation user interface.

Ok thanks I will try this out. But it would be nice to use standard lift features for this... :-)