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From Rex Wang <rwo...@gmail.com>
Subject Re: Implementing rfc66 in Geronimo
Date Thu, 14 Jan 2010 09:27:38 GMT
2010/1/14 Jarek Gawor <jgawor@gmail.com>

> Hey all,
>
> I've been looking into implementing rfc66 support in Geronimo a little
> bit more. Here are some things that we need to do and my
> thoughts/impressions about them:
>
> 1. WAR to WAB converter. Installs webbundle: url handler that converts
> standard WAR files into Web Application Bundles (WAB). The converter
> code was contributed by IBM to Apache Aries but so far it has not been
> moved to trunk yet. This code will probably need some updates but I
> think we could just mostly use it as it is in Geronimo.
>
> 2. WAB extender. Watches for WABs to be started in the framework and
> performs the necessary steps to deploy the applications.
>  a. In Geronimo we will need a custom extender that effectively
> invokes Tomcat/JettyWebModuleBuilders to deploy the application. There
> might be an extender implementation donated to Aries at some point but
> I don't think we will be able to use since it most likely will use the
> Tomcat or Jetty API directly to deploy the application. In Geronimo we
> build the GBeans which then use Tomcat/Jetty API to set everything up.
>  b. The biggest issue that I see with Geronimo WAB extender is
> updating the WebModuleBuilders (or actually the whole deployment
> process) to work with Bundle objects. Right now the deployment process
> for the most part assumes it is working with JarFiles.
>
So, what is the standard method to install/deploy a WAB into Geronimo 3.0?
>From the osgi perspective, that should be the same with installing a normal
bundle to framework, and then the extender will track this and help deploy
it to geronimo by instantiating some gbeans. Should we support the geronimo
deployment process such as deploy a WAB with a external plan?

 c. Rick has some initial extender code in the sandbox that we should
> be able to reuse (or at least parts of it) in Geronimo.
>  d. Things to keep in mind:
>    1. The specification talks about support for lazy bundles. More
> specifically, that a request on static resource of a lazy activated
> bundle should not cause the bundle to become fully activated.  This
> might be tricky to implement in Geronimo and would require changes to
> existing code. However, support for lazy bundles seems to be optional
> in the specification.
>    2. The specification says that “it should be possible for a Web
> application bundle to remain installed when its Web Container is
> dynamically replaced”. Which I think it means what happens if somebody
> deploys WAB, then stops Tomcat container and starts Jetty container
> all at runtime. Does the application continue to work? Should Geronimo
> support this case? It is an optional feature.
>
Does that indicate each WAB will contain several plans for different
containers? That might require a way to distinguish the plans.

   3. The extender might need to track somehow which WABs were
> already deployed to prevent double start problems. Once some WAB is
> deployed and the Geronimo server is restarted, Geronimo will attempt
> to start the generated configuration/plugin for the WAB. Starting of
> the plugin will also start the actual WAB and then the extender will
> see the starting bundle and attempt to deploy the WAB again.
>
Yes, I think the other RFC66 implementation also need to take care of it.

Thanks
-Rex


>
> 3. Annotation and resource discovery.
>  a. The specification does not describe an exact way of discovering
> annotations or resources in a WAB. For example, if WAB imports some
> package from another bundle, are all classes in that package scanned
> for annotations? What about resources in META-INF directory? Are the
> bundles wired to the WAB checked for META-INF resources?  These are
> some unanswered questions that we need to keep track of.
>  b. In certain cases (e.g. servlets 3.0, EJBs, etc.) we will need to
> discover all accessible classes in bundle class space that have a
> given annotation. For that we will need annotation discovery code that
> might need to know how to scan bundles based on Bundle-Classpath and
> possibly on Import-Packages, DynamicImport-Package, Require-Bundle,
> etc. depending on what the specification will say. The annotation
> scanning code might get even more difficult if it needs to support
> lazy bundles.
>  c. Tag library scanning might require similar code as used in
> annotation discovery since the tld files can be included in any
> directory in a JAR under the META-INF directory. This also depends on
> what the final specification will say.
>
> 4. JSP Runtime Compilation. Not sure yet what that will require (if
> anything).
>
> 5. JNDI (RFC 142) integration. Get services from service registry
> using JNDI lookup using osgi:service/<interface> name (and therefore
> OSGi services could be injected via standard @Resource annotation).
> Support for RFC 142 is recommended but not required by RFC 66. This is
> an optional item but useful to have. There is RFC 142 implementation
> in Apache Aries that seems pretty complete so it just needs to be
> integrated in Geronimo.
>
> I think updating the WebModuleBuilders (2.b) will take the most time
> and effort. The annotation and resource discovery (3.b and 3.c)
> shouldn't be a lot of work but it's still not very well defined in the
> specification and that is something we need to keep track of. The good
> news is that we can work on all (except maybe the JSP compilation) of
> these items at the same time without stepping on each other's feet.
> Also, if the specification decides to require support for lazy bundles
> that will cause some fairly major changes in Geronimo. For now, I
> think we should assume that lazy bundles are optional and assume
> fairly simple rules for annotation and resource discovery code (i.e.
> scan jars files or directories specified on the Bundle-ClassPath
> only).
>
> Comments?
>
> Jarek
>



-- 
Lei Wang (Rex)
rwonly AT apache.org

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