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From Jarek Gawor <jga...@gmail.com>
Subject Implementing rfc66 in Geronimo
Date Wed, 13 Jan 2010 16:37:58 GMT
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.
  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.
    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.

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

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