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From Elliot Metsger <emets...@jhu.edu>
Subject Re: Embeddable Pluto 2.0 container for Jetspeed-2
Date Thu, 14 Feb 2008 01:53:15 GMT
Sorry Ate, everyone, for the delayed response.  Life happens, right? :)

First I am totally supportive of getting Pluto 2 to work with JS.  The 
rest is just details :)  I know there are other projects (uPortal, 
Sakai) which have migrated to and embedded (respectively) Pluto 1.1.

Ate Douma wrote:

<snip>

> 
> The Pluto 1.0.x object model API (OM)
> =====================================
> Pluto 1.0.x provided a fully interface based object model to represent 
> the web and portlet deployment descriptors (web.xml and portlet.xml).
> Through factory methods, the Pluto 1.0.x container only used these 
> interfaces in its implementation. That allowed Jetspeed and other 
> portals to supply its own
> implementation of the OM and use that to provide enhanced features like 
> database persistence, extended meta data, caching control, etc.
> Of course, Pluto 1.0.x also provided its own implementation classes of 
> the OM and Jetspeed uses these as base classes but provides extended 
> implementations to
> hook them up and into its own backend and management features.
> 
> Pluto 1.1.x completely dropped all of this. Instead, a new descriptor 
> API was provided with a complete new set of classes (no interfaces!) 
> which are used and
> instantiated directly within the container with no factory support or 
> any other way of extending the current implementation.
> As such, the current container only allows usage of the web.xml and 
> portlet.xml descriptors and features derived from them as provided by 
> the container.
> Furthermore, as the loading and management of the descriptors is now 
> done directly (and only) by the container itself, there is no way for 
> Jetspeed to hook into
> this process anymore.
> 
> Effectively, this means that descriptor persistence, caching, custom 
> extensions, *standard* support for custom portlet mode or window-state 
> mapping,
> etc. all no longer are possible with the current Pluto container. Not 
> just for Jetspeed but any portal needing and depending on these features.

Here are my comments on the Descriptor OM.  There was an intentional 
design decision made with the 1.1 descriptor om: specifically that no 
behaviors or responsibilities are attached to model.  The model is 
orthogonal to the behaviors.  Restricting the OM to what are essentially 
just beans or value objects makes it easy for embedders: they aren't 
forced to implement a bunch of interfaces.  And if they want additional 
behaviors like persistence they can add them in the portal implementation.

uPortal for example (and Eric correct me if I'm wrong) has a relatively 
straight forward model of portlet -windows, -entities, -deployments, and 
applications and has a hibernate-based implementation for persisting them.

A little off topic, I think there improvments that need to be made to 
the descriptor impl - Eric Dalquist has some good ideas.  The goal there 
being to load the descriptor impl from the webapp classloader instead of 
having to pollute a shared classloader with the descriptor impl and all 
of its dependencies.


> The Pluto 1.1.x/2.0 PortletContextManager, PortletDescriptorRegistry and 
> PortletServlet
> =======================================================================================

> 
> With the switch to Pluto 1.1.x, the container added control and 
> management of the above mentioned deployment descriptors and fully 
> integrated them with the
> container interaction which now depend on this management 
> *implementation*, and also hooked that up on the portlet application 
> context.
> This means that now you need a separate container instance for each 
> portlet application and that the container itself loads and manages the 
> descriptors.

I'm not sure what you mean here.  Generally the pluto container, along 
with the descriptor api and impl are deployed in a shared classloader, 
so you only need one instance.

> Also, interaction with the container now requires the use of the Pluto 
> provided PortletServlet (although that one possibly can be extended) as 
> it is tied to the
> PortletContextManager directly (which in turn is tied to the 
> PortletDescriptorRegistry).

What about Jetspeed providing its own "PortletServlet" implementation. 
The portlet servlet is pretty simple, initing the portlet, fixing up the 
request and response and dispatching to the container.  You'll need to 
have the assembler use your servlet implementation when assembling web.xml.

> Besides the obvious problem that this effectively blocks delegating 
> management of the context and descriptors for the portal, it also forces 
> the usage and
> interaction with portlets to the Pluto provided implementation.
> For instance, Pluto delegates interaction to each portlet through a 
> separate instance of its PortletServlet, while Jetspeed currently has 
> its own more generic
> JetspeedContainerServlet which is not tied to a single portlet. The 
> Jetspeed solution allows for dynamically enabling/adding portlets (as 
> defined in
> portlet.xml) without any need to rewrite the web.xml. But using the 
> Pluto PortletServlet requires changing the web.xml (and thus reloading 
> the context) to do so.

Normally the container will sit in a shared classloader, so there is 
only a single instance of PortletServlet in a JVM.  When PortletServlet 
is initialized, it registers the available portlets with the 
RegistryService.

The Registry Service is an interface and a portal can have its own 
implementation.  You can dynamically register new portlets on the 
registry service.

> 
> The Pluto 1.1.x service provider interfaces (SPI)
> =================================================
> Although the new Pluto SPI (comprising of the RequiredContainerServices 
> and OptionalContainerServices) generally provides a nice and simple 
> interface to plugin
> portal specific implementations, certain features available with Pluto 
> 1.0.x are no longer available.
> 
> With Pluto 1.0.x, critical components as the PortletContext and 
> PortletWindow were accessed by the container through factory classes.
> These no longer exist and the pluto container directly instantiates its 
> own implementations for these components.
> 
> Jetspeed however very much depends on its own extensions of these 
> components to provide support for features like parallel rendering, 
> clustering and attaching
> additional meta data (or even preferences) to a PortletWindow or 
> PortletEntity.
> Additionally, while Pluto 1.0.x allowed managing multiple PortletWindows 
> for a PortletEntity, this *Portlet Spec* feature has been removed from 
> the current
> Pluto 1.1.x/2.0 container.
> 
> Lastly, not all of services referenced through these SPI interfaces are 
> only accessed through it.
> For instance, the OptionalContainerService.getPortletRegistryService() 
> is by default implemented by the PortletContextManager. But, this 
> implementation is very
> much directly used (as static instance even) within the container. 
> Effectively, the interface is now only an API portals might use, but it 
> cannot be replaced
> and thereby cannot be regarded as a proper SPI interface anymore.

Let me come back on this issue, I need to look at the code a bit more to 
understand.  I do see where PCM is used instead of the interface.  It 
may be easy to switch to using the interface.  E.g. PortletContainerImpl 
already has a reference to OptionalContainerServices so looking up the 
Registry Service by interface instead of instantiating PCM directly 
should be doable.  There may be classloader issue.

In general there should be a way to inject the impl that you require. 
If there isn't a way, there's definintly a problem that we need to 
design/code a solution to.

> 
> Solution
> ========

I gotta run now but I'd like to take some more time and reply in more 
detail, icluding commenting on the solution.

Thanks Ate and JS team for bringing these issues up!

Elliot

> As indicated earlier, solving the above issues such that Pluto 2.0 can 
> be made embeddable again, in Jetspeed or other portals, needs to be done 
> in a way which
> maintains backwards compatibility for current Pluto 1.1.x users.
> 
> Although we don't have a clear proposal for this, our current idea is to:
> - define new OM interfaces to be implemented by the current descriptor 
> api classes
> - enhance the OptionalContainerServices SPI to provide additional 
> services for loading and managing the deployment descriptors
> - enhance the OptionalContainerServices SPI to provide additional 
> services for accessing components like PortletContext, PortletWindow etc.
> - refactor the container implementation to only use the OM interfaces
> - refactor the container implementation to only use the SPI provided 
> services and no longer directly binding to its service implementations
> 
> When done properly, the above changes should still allow using the 
> current implementation without any functional or even technical 
> consequence.
> 
> Now, the above changes will mean a lot of work and lots of testing as 
> well to make sure everything remains working as expected.
> We, as primary Jetspeed committers have much at stake here so we are 
> definitely willing to help out and do much of the grunt work.
> And of course, we will have a large amount of work to do at Jetspeed 
> Portal side as well: all our Pluto Factory implementations have become 
> useless, all Pluto
> OM packages (and some interfaces) have changed, and we will need to 
> provide new implementations for the Pluto SPI container services.
> 
> For our implementations of the Pluto SPI container services, we will 
> definitely look at the current Pluto provided implementations and where 
> possible try to
> make use of them as much as possible. To that end, we will probably also 
> need to be able to hook in our own extensions which might require some 
> additional
> refactoring but should not result in functional or technical changes of 
> the default Pluto services.
> 
> Note: we want to migrate to Pluto 2.0 for our next Jetspeed 2.2 release. 
> But, for that release we'll stick to only using the JSR-168 container 
> features.
> Then, for the following major release, version 2.3 which we currently 
> have scheduled sometime this summer, we will provide full JSR-286 
> compliance.
> So, our initial goal is to get Pluto 2.0 working again with Jetspeed-2 
> but stick to our current features.
> 
> This all is clearly not something which can be done or will be ready 
> overnight, nor possible to do all by ourselves.
> But we do need to start resolving this ASAP so it won't hold up the 
> release of both Pluto 2.0 and Jetspeed 2.2 longer than needed.
> 
> As said: the above proposal is still just an idea. And of course how to 
> do all this, is fully open for debate and we are very interested in 
> hearing the opinions
> of other committers and community members (also from other portals 
> embedding Pluto 1.1.x).
> 
> So please, provide feedback and ideas how to solve these issues. And 
> suggestions for alternative solutions will very much appreciated too!
> 
> With kind regards,
> 
> Dennis Dam
> David Sean Taylor
> Ate Douma
> 

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