It seems changing the default SCDL location names so they are unique does not
prevent using classloaders to keep the artifacts from each isolated. Doing this
only allows the flexibility that they COULD more easily coexist in the same
classloader scope. Given we see the core as something that maybe reused and
embedded in many ways, why would we not want to take path that would be more
flexible ? So far, I really don't see any disadvantage in changing to this.
Raymond Feng wrote:
Please see more comments below.
Raymond
----- Original Message ----- From: "Jim Marino" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, August 25, 2006 10:27 AM
Subject: Re: Avoiding extension and application scdl collisions
On Aug 25, 2006, at 9:32 AM, Raymond Feng wrote:
Hi,
It's a bit challenging to run a simple SCA J2SE helloworld sample.
Here's the folder structure you have to deal:
helloworld
--- bin: the launcher.jar, sca-api.jar and host-util.jar
--- boot: core.jar, spi.jar, etc
--- extension: axis2.jar (optional)
helloworld.jar
Then you can use the launcher to run helloworld sample.
I fully understand the value of isolation for different level of
code. I just have a feeling maybe it's too much for a poor J2SE user
to get the basic sample working.
Ah so this is referring to J2SE client (i.e. from main) and not in a
managed environment. I still think this is not that big of a deal.
I personally prefer to have directories where I can stick things than
a huge classpath. It also avoids the pain of package collisions with
application code. Embedded Jetty works like this and I've found it
pretty straightforward.
I'm not against the isolation which is definitely required for a managed
environment. I also agree with you that a huge classpath is not the best
pratice even for J2SE. I just wonder if it's still possible for a dummy
user to choose one single classpath to include everything.
People will also still have to deal with SCDL anyway and that should
be in a well-defined location. Having extensions in a well-defined
location does not seem to be an additional burden.
I'm seeing inconsistency in some places that we still use
ClassLoader.getResource() to resolve URLs which seems to me that it
violates the idea of "isolation by location". For example, we use
ClassLoader.getResource("META-INF/tusacny/system.scdl") for the core and
ClassLoader.getResource("META-INF/sca/default.scdl") for the application.
More importantly, if we are trying to make the use case of a single
reference used by a J2SE client easier, I'd would say don't use SCA
for that. Just use Axis (or some other transport) directly. Where SCA
is valuable is in assembly of multiple services.
I'm not sure :-) I think it should also be possible for these guys to
take advantage of SCA (I assume SCA can simplify programming).
I have some related questions here:
1) Is it possible to use SCA with Tuscany inside a traditional J2SE
application with a flat classpath?
Can you give a more detailed use case? If it is just accessing one
service, or a couple, then my answer would probably be the same as
above: use the transport directly, it will always be much easier. If
you want to have an application with one SCA service in it wired to
others, then a container needs to be deployed and it is not an "J2SE
application" anymore, it is an "SCA application running in a J2SE host".
I was thinking about adding SCA capability into an existing J2SE app.
2) Where should the dependency jars go? It includes the dependency
jars for core runtime and extensions.
I'm not sure I follow, what is "it"?
For example, our Axis2 bining has dependencies on Axis2 jars and our
core has dependencies on StAX. Where should these jars go?
3) Can I have one extension depend on another extension?
Sure, in which case we need to calculate the transitive closure of
all dependencies and adjust classpaths accordingly. OSGi will do this
for us.
I like OSGi too. Why don't we leverage OSGi in the core instead of
reinventing the wheels?
Thanks,
Raymond
----- Original Message ----- From: "Jim Marino"
<[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, August 25, 2006 8:59 AM
Subject: Re: Avoiding extension and application scdl collisions
On Aug 24, 2006, at 10:50 PM, Raymond Feng wrote:
Hi,
I understand we endeavor to support isolated classloading for
system, extension, and application. But I think we should be able
to run a SCA application with the runtime and extension jars on
its classpath if the user chooses to do so.
Could you explain your reasons why? The only case where I can see
this being a good thing for the user is if an extension offers
APIs or libraries that must be accessed from the application. In
that case, those APIs or libraries should be loaded in a parent to
the extension classloader which is then given as a parent to the
application classloader (which would be multiparent).
Jim
To be consistent with the SCA spec (xxx.composite), I suggest
that we have the following conventions.
core: META-INF/tuscany/system.composite (with includes)
extension: META-INF/tuscany/extension.composite
application: META-INF/sca/application.composite
Thanks,
Raymond
----- Original Message ----- From: "Rick" <[EMAIL PROTECTED]>
To: "tuscdev" <[email protected]>
Sent: Thursday, August 24, 2006 9:26 AM
Subject: Avoiding extension and application scdl collisions
I kind of have and closer idea why interop unit testcases fail
when run from the maven command line. It appears the forking
for some reason I'm still not 100% sure of puts the
Axis2Binding jar in the same classloader as the application
scdl. It could be the fork actually has dependencies need by
the testcase already on the classpath? In any case when the
application scdl is being search for it is being found in the
extension jar because the default resource name is the same for
both extensions and application scdl (META-INF/sca/ default.scdl)
I can for the testcase specifically rename the application scdl
to something different and it then works. To avoid this and
also provide the flexibility to load in one classloader scope
would having default names as follows be reasonable?:
META-INF/tuscany/system/system.scdl. (system)
META-INF/tuscany/extension/default.scdl (extensions)
META-INF/sca/default.scdl (application)
(not too sure how this plays with the SCA archive proposal)
Also, I'm wondering if it is already possible, if we could add an
xml attribute to system and extension scdl to identify it as
such so when we are expecting one type and it does not have
this attribute we throw an exception? This would have been a
whole lot more helpful to me than the resulting NPE?
Thought?
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