Here's a few things I think about when considering API versioning:
1. How many implementors are there? It sounds like there will be one -
Struts2
2. Do you want to allow implementors to implement multiple APIs? Sounds
like yes.
3. How much is shared between APIs? Probably a lot.
From what it sounds like, and correct me if I'm wrong, you are looking
to do something like this:
API 1.0----------\
|----------- Struts2
API 2.0----------/
If this is the case, it will require some interesting coding tactics.
Sun and IBM have some white papers on these types of cases. OSGi will
shield the two APIs from each other so there aren't any conflicts,
however, the implementor will have the unfortunate task of implementing
both. This becomes difficult without proper structure at compile time
because struts2 will need to implement multiple interfaces from both
versions and these interfaces might overlap.
I've done some of this type of work before and in order to truly break
compatibility between 1.0 and 2.0, you need namespaces in order to allow
Struts2 to implement both. Otherwise you get naming conflicts that
cannot be resolved by the compiler. I've do things like this before:
org.apache.struts.api1.SomeInterface
org.apache.struts.api2.SomeInterface
This is the same interface, but breaks compatibility between the API
versions. Only by separating the namespaces will you be able to
implement both at compile time. I've also worked with other situations
like this:
org.apache.struts.api.SomeInterface_1_0
org.apache.struts.api.SomeInterface_2_0
What it comes down to is that if you are going to break compatibility at
the API level you need to actually create a brand new API. When you look
at it from this perspective, OSGi really isn't needed, just nice to
have. Since the two API versions are in different namespaces, there
aren't any collisions at compile-time or runtime, eliminating the need
for bundle separation.
Having done some of these types of solutions before, I can attest to the
pain that they can cause. They can also become complex to manage. Which
sorta leads back to my original statements about compatibility. I'd much
rather see something like this:
1. The APIs locked down
2. These APIs called Struts3
3. No APIs break compatibility until Struts4
Therefore, 3.0, 3.1, 3.2, etc are all compatible. Then when Struts4
start wanting to break compatibility, you branch Struts3, and start
breaking away on Trunk.
-bp
Don Brown wrote:
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
---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
