Introduction
This proposal briefs the limitation we see with current server publish API,
and it suggests a solution. We had a short discussion during a conference call
on Mar 13th, 2006. (mainly around the ServerBehaviourDelegate). The
problem is also related to https://bugs.eclipse.org/bugs/show_bug.cgi?id=123676
Current API
We learned the original design was driven by a need of a very simply
publish mechanism.
- an adopter should
able to implement a simply delegate and do the publish work.
- publish tasks was intent
to be simple task.
- most methods can be overridden.
BEA use-cases
We found the current API is not ideal for BEA needs.
We delay much of publish process until user do an explicit publish
action (menu item publish, or Run on Server).
- We generates *.java
file based on annotation of Java file in publish time. We trigger project rebuild
during process.
- We insert
information into application descriptors (web.xml, application.xml) based
on files on the project.
- Generated artifacts can
cause changes to the EAR or other modules in the same application.
- Publish application
by application.
- Publish failure
should be isolated between modules.
For us, the publish process is better described as a 3 steps process: Assembly
(artifact generation), Packaging (we package virtually), and Distribution
(calls JSR-88 to distribute the application to the server).
Limitation
The current SPI was driven by the need of simple publishing. The
publish process iterates module by a flattend module list (not application by
application.)
Because that most methods can be overridden, we can achieve our goal
reasonably well. However, it incurs maintenance risk, because are not really
implementing the delegate’s SPI. For example,
- if a fix or an enhancement
is made to PublishOperation, our server adapter lag behind, and
enhancement will not be supported.
- We short circuit a
few methods, such as publishModules() (which is a violate the interface). If
any of the methods is called by new code that we haven’t overridden,
it causes unexpected behaviour.
Because of the different design goal, we don’t implement the full
spec of ServerBehaviourDelegate. While such changes might not be likely, an
adopter should not be required to implement their delegate in a way to violate
the SPI contract.
Solution
Required changes
We can eliminate the problem by the following changes:
- Introduce another delegate.
Let’s call it BaseServerBehaviourDelegate for now. The current ServerBehaviourDelegate
should make extended of BaseServerBehaviourDelegate. Most generic methods
can be push up. (such as state settings, module controls, resource delta maintaince.
But, it leaves out
- code related to published
module list, and the kind. PublishOperation, and
- all the publish
methods. Introduce an adapter interface to indicate PublishOperation is supported.
The changes will maintain compatibility for all
current adopter, and the original design goal. It enables adopter with
different needs to have full control of the publish process.
-
- Either, makes publish
operation optional. Push down PublsihOperation related code to the
original ServerBehaviour Delegate.
- Or, factors out
PublishOperation into utility class or method.
- Or, made
PublishOperation not depends on the flatten module path (IModule[]
representing the sub module and its parents).
- Introducing another
extension point for UI to replace the hard-coded publishTask page fragment.
Move UI for publishOperation as an extension.
A brief study of the code indicated that we should able to implement it
in a way that it doesn’t affect existing adopter.
Optional changes
A few optional changes can be introduced to ease the work of an
adopter.
- Publishing application-by-application
is common to many servers. We might want to introduce another BehaviourDelegate.
- Generic server is
already use application-by-application approach. We should look into
merging the requirements.
- Going further, we
can also introduce the 3 steps publish process for adopter with
complicated publish use-case.
--------------------
Thomas Yip
Senior Software Engineer
BEA Systems
Email: tyip@xxxxxxx
YIM: thomasleaf Phone: (206) 926-2906 Blog: http://theBigGrid.com/
"The complexity you remove can never
fail." Burt Rutan.