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From "Don Brown" <mr...@twdata.org>
Subject [s2] A thought - next generation OSGi-based?
Date Thu, 24 Apr 2008 16:09:20 GMT
As I learn more and more about OSGi, I wonder if it might be the
solution to several big problems we seem to have at the moment: poor
reloadability and the lack of a solid API.  With OSGi, you can drop
bundles in and out of the system at runtime, even running multiple
versions of the same bundle side-by-side, but the feature I'm most
interested in right now is how it would allow us to put in a proper
API while maintaining full backwards-compatibility.

Evolving a web framework is hard because apps tend to be written on a
specific version, and to migrate them to new versions has two
problems: development may not be continuously funded and the upgrade
may require too many changes to the application.  On the other hand,
if you don't evolve your web framework, you quickly go out-of-date and
lose interest from new developers.  In our case, despite being a
relatively new framework, we have legacy code around from 2004 that we
can't just remove, yet we want to provide an attractive, modern, clean
framework for new development.

The specific issue it hand that I've been thinking about is how to get
a proper API into Struts 2 yet keep backwards compatibility, and I
think OSGi might provide a solution.  What about this:
 1. Struts 2 and its plugins remain the way they are now - 100%
backwards-compatibility
 2. An OSGi plugin provides the platform for the next generation of Struts 2
 3. A new API bundle is created, implemented by the underlying Struts
2 framework
 4. Old apps can continue to write and deploy code against Struts 2,
yet new development can start to use the new API
 5. Later, when we want to write API version 2, we create a new bundle
that runs side-by-side the old bundle, both implemented by Struts 2

Basically, OSGi would allow us to write a clean layer on top of a
framework, much like how Grails builds on Spring, but we get, as a
side benefit, all the architectural advantages of OSGi for free.
Furthermore, if we do it right, users don't have to know or care that
OSGi is under the hood - all they know is they write a jar, drop it in
a directory or upload it via a form and they just installed part of
their application at runtime.

Don

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