On Jun 21, 2006, at 1:30 PM, Raymond Feng wrote:
Hi,
I guess one of the concerns is that some of the base classes create
additional contracts which are not captured by the interfaces. It
ends up that the extension developers have to understand more.
Actually, I think they have to understand less. Using the base
classes, they do not need to worry about how to register and
deregister the loaders. Do you feel the loader extensions are too
complicated? If so, what would an easier one look like?
Let's use the "StAXElementLoader" and "LoaderExtension" as an
example. Interface StAXElementLoader only requires the "load"
method to be implemented while "LoaderExtension" defines a contract
on how a StAXElementLoader register/deregister with the
LoaderRegistry. This is achieved by java annotations.
For this particular case, I can see two ways to get an extension
picked up by the runtime: declarative or programmatic. Some further
questions will be:
1) Should the extension developers have a choice to use either java
annotations or external XML configuration?
2) Should the extension metadata (for example, the XML element name
that a loader can handle) be captured in a model and java
annotation is just a convenient way to supply the value?
We had decided the system service model would be based on annotations
a while back. I'm happy to revisit but I don't see any value in
allowing for external configuration of *component type* data. This is
also consistent with the SCA programming model which views external
component type metadata for Java C&I POJOs to be primarily for
"legacy code".
Thanks,
Raymond
----- Original Message ----- From: "Jean-Sebastien Delfino"
<[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, June 21, 2006 2:08 AM
Subject: Re: Tuscany SPI interfaces
Jim Marino wrote:
I think you missed something. With core2, most people will extend
from the helper abstract classes in the SPI extension package
(this was also the case with the previous core). For example:
I didn't miss this class, as I said that's exactly what I'm trying
to avoid. I want to implement the SPI interfaces without having to
extend base implementation classes.
public class FooAtomicComponent extends
AtomicComponentExtension<Object>{
public FooAtomicComponent(String name, CompositeComponent<?>
parent, ScopeContainer scopeContainer, WireService wireService) {
super(name, parent, scopeContainer, wireService);
}
public Object getServiceInstance() throws TargetException {
return null;
}
public Object createInstance() throws ObjectCreationException {
return null;
}
public Object getServiceInstance(String name) throws
TargetException {
return null;
}
public List<Class<?>> getServiceInterfaces() {
return null;
}
public TargetInvoker createTargetInvoker(String serviceName,
Method operation) {
return null;
}
}
I generally don't like to "count" methods without looking at what
they do (e.g. some could just be setter/getter types). The above
class contains 5 methods, which I believe are reasonable and we
don't want to separate out. Invoker is very simple too:
- Two methods to invoke, one for "message" invocations, and one
for raw payloads. Generally, the first will just pull the payload
and invoke the second
- A setter/getter pair for whether the invocation is cacheable
- A boolean if the invoker can be optimized away and the target
can be called through straight invocation without a proxy.
Generally false.
- A clone method
The Spring and Groovy samples in the sandbox demonstrate both of
these.
Jim
On Jun 21, 2006, at 1:37 AM, Jean-Sebastien Delfino wrote:
I'm trying to implement the sample ruby extension and running
into some issues.
I'm implementing an AtomicComponentContext (with the code in the
head stream) and also trying the equivalent AtomicComponent with
some of the code in the sandbox. I want to be able to implement
my extension class without having to depend on base Tuscany
runtime implementation classes, so I'm just implementing the SPI
interfaces.
Unless I missed something (and it's very possible since I don't
understand all the pieces yet) here's what I found:
- with the code in the head, my AtomicComponentContext needs to
implement 15 methods;
- with the code in the sandbox, I have to implement 25 methods.
And this is just one class, I'm not even implementing the
builders or invokers yet... I think that in both cases this is
too much.
It looks like the experiment in the sandbox is attempting to
provide a simpler programming model for these extensions by
hiding some of the complexity in base implementation classes,
but I think it will be better to define a set of independent
interfaces and make some of them optional. In other words if my
extension does not wish to implement one of the interfaces, then
it just doesn't need to, and the runtime should assume some
default behavior, instead of forcing me to implement all the 25
methods...
Another thought is to allow the contract to be implemented with
multiple objects specialized in each aspect instead of one big
object with 25 methods.
As I'm going through the implementation of the ruby component
implementation extension, I'm trying to come up with a short
list of requirements and methods that I think we really need to
implement, and with that list I'd like us to prototype simpler
SPI interfaces. If anybody is interested in helping, please feel
free to jump in, it would really be great if we could do a
binding extension in parallel, and also if the people who
actually developed some of the existing extensions could come up
with the requirements they've seen in terms of SPI and proposals
to improve our extensibility story.
Thanks,
--Jean-Sebastien
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