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From Ate Douma <...@douma.nu>
Subject Embeddable Pluto 2.0 container for Jetspeed-2
Date Fri, 08 Feb 2008 19:18:27 GMT
Dear committers, community,

Jetspeed-2 currently still uses Pluto 1.0.1 as its JSR-168 container, but we want and need
to upgrade and migrate to the latest Pluto container under
development, aka the not yet released Pluto 2.0 targeted as the JSR-286 RI.

This however is currently impossible to do because of the architectural changes Pluto underwent
from version 1.0.x to 1.1.x.

Technically, viewed from the POV of an easy to embed container for the Pluto Portal Driver,
or environments which only need the out-of-the-box features
provided, these architectural changes have resulted in a much simpler and easier to understand
and maintain model and API, and as such these changes were great!

But... for a portal like Jetspeed-2, which provides a much enhanced usage and feature list
*on container level*, these architectural changes have, simply put,
completely broken with the functional and technical "contract" provided by Pluto 1.0.x and
as such make it now impossible for us to migrate to the current Pluto
container.

As it is the primary mission and goal of the Pluto project to provide an embeddable portlet
container for portals like its Apache Portals sibling project
Jetspeed-2, it is our view (as Jetspeed-2 committers) that we need to discuss what needs and
can to be done, on both Jetspeed-2 and Pluto side, to bring our
projects back together, and how to restore the original *functional* contract Pluto provided
with version 1.0.x.

To this end, we'll present our (short) assessment how the current Pluto container API and
implementation has changed and broken with the old Pluto 1.0.x
features which Jetspeed-2 depends upon to be able to maintain our current Jetspeed-2 features,
as well as what we think needs to be done *functionally* to
restore these features.

To be very clear: we're not asking nor suggesting to restore the old Pluto 1.0.x API and SPI
as is. We fully expect and are willing to adapt Jetspeed-2 to the
new Pluto architecture as much as needed, even while that most likely will now cause Jetspeed-2
itself to have to break with its own public API and thus lose
(some) backwards compatibility. After all, Pluto now has had several releases based on its
new Pluto 1.1.x architecture and we (as Apache Portals community)
have the obligation to maintain as much backwards compatibility for the users of these versions
as well.

So, what we will propose later on is to work towards a solution which will restore the ability
for Jetspeed to properly use and embed the new Pluto 2.0
container but still maintain the lightweight and simple configuration and usage of the container
for portals like the Pluto Portal Driver and other use-cases
without breaking its current "contract".

But first lets get down to some of the issues we have identified so far. This is most likely
not the complete list but covers the most important ones.

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.

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.
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).

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.

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.

Solution
========
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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