Tomcat uses JNDI to load resources, including JSP pages

["Noel J. Bergman" <no...@devtech.com>]

Guys,

See:
http://nagoya.apache.org/eyebrowse/ReadMsg?listName=geronimo-dev@incubator.a
pache.org&msgNo=5874

Craig provided a nice explanation of how tomcat loads resources.  Highlight:

  Basically, Tomcat models the static resources of a web application
  as a JNDI DirContext, with nested DirContext objects for nested
  "directories" in the WAR.  [Two] implementations are included --
  one for running webapps out of [a directory and one for running
  from a WAR.]  All the access details [are] hidden inside these
  implementations.

I did not realize, but am seriously pleased to know, that tomcat worked that
way.  This is really wonderful news.  Any data source for which we can write
a JNDI provider is capable of hosting web resources.  That could include:

  - a Subversion repository, via WebDAV
  - an LDAP database
  - an RDBMS
  - a CVS repository

Anyone getting excited about the possibilities, yet?

	--- Noel

Re: Tomcat uses JNDI to load resources, including JSP pages

["Craig R. McClanahan" <cr...@apache.org>]

Quoting Phil Steitz <ph...@steitz.com>:

> Noel J. Bergman wrote:
> > Guys,
> > 
> > See:
> >
> http://nagoya.apache.org/eyebrowse/ReadMsg?listName=geronimo-dev@incubator.a
> > pache.org&msgNo=5874
> > 
> > Craig provided a nice explanation of how tomcat loads resources. 
> Highlight:
> > 
> >   Basically, Tomcat models the static resources of a web application
> >   as a JNDI DirContext, with nested DirContext objects for nested
> >   "directories" in the WAR.  [Two] implementations are included --
> >   one for running webapps out of [a directory and one for running
> >   from a WAR.]  All the access details [are] hidden inside these
> >   implementations.
> > 
> > I did not realize, but am seriously pleased to know, that tomcat worked
> that
> > way.  This is really wonderful news.  Any data source for which we can
> write
> > a JNDI provider is capable of hosting web resources.  That could include:
> > 
> >   - a Subversion repository, via WebDAV
> >   - an LDAP database
> >   - an RDBMS
> >   - a CVS repository
> > 
> > Anyone getting excited about the possibilities, yet?
> 
> Yes, this is very cool. This is also a big help to me in grokking Tomcat's 
> JNDI use cases.  I have been (slowly, sometimes with much puzzling) trying 
> to assemble an initial set of tests for the naming code, based on Tomcat's 
> uses. Thanks, Craig!
> 
> I am still not clear on what is specific to Tomcat in terms of web 
> resource loading and what could be made generic (so that the contexts that 
> we could provide would be useful to other containers). Hopefully, this 
> will become clearer as I make my way through the code.
> 

It's been a little while since I looked (I've been active on other things for
the last couple of years, and am primarily lurking on TOMCAT-DEV at the
moment), but here's a few things that might be considered Tomcat specific:

* Configuration of the initial contents of the JNDI context for the
  static resources is all hard coded -- there's no externally
  defined mechanism at the moment.

* Only the entry attributes that a servlet container cares about
  are exposed (create timestamp, size in bytes).

* The ability to recreate the contents of the context (used when
  a webapp is reloaded) is probably Tomcat-specific.

None of this is all that hard to deal with in a refactoring.

When looking at the code, you should also note that Tomcat also creates a
separate in-memory JNDI context for the environmental resources defined in the
web application deployment descriptor (<env-entry>, <resource-ref>, ...).  I
guess that counts as a third JNDI implementation, but the one that deals with
the things you are talking about starts from
"org.apache.naming.resources.BaseDirContext".


> Phil
> 
> > 
> > 	--- Noel
> > 
> 
> 
> 

Craig

Re: Tomcat uses JNDI to load resources, including JSP pages

[Phil Steitz <ph...@steitz.com>]

Noel J. Bergman wrote:
> Guys,
> 
> See:
> http://nagoya.apache.org/eyebrowse/ReadMsg?listName=geronimo-dev@incubator.a
> pache.org&msgNo=5874
> 
> Craig provided a nice explanation of how tomcat loads resources.  Highlight:
> 
>   Basically, Tomcat models the static resources of a web application
>   as a JNDI DirContext, with nested DirContext objects for nested
>   "directories" in the WAR.  [Two] implementations are included --
>   one for running webapps out of [a directory and one for running
>   from a WAR.]  All the access details [are] hidden inside these
>   implementations.
> 
> I did not realize, but am seriously pleased to know, that tomcat worked that
> way.  This is really wonderful news.  Any data source for which we can write
> a JNDI provider is capable of hosting web resources.  That could include:
> 
>   - a Subversion repository, via WebDAV
>   - an LDAP database
>   - an RDBMS
>   - a CVS repository
> 
> Anyone getting excited about the possibilities, yet?

Yes, this is very cool. This is also a big help to me in grokking Tomcat's 
JNDI use cases.  I have been (slowly, sometimes with much puzzling) trying 
to assemble an initial set of tests for the naming code, based on Tomcat's 
uses. Thanks, Craig!

I am still not clear on what is specific to Tomcat in terms of web 
resource loading and what could be made generic (so that the contexts that 
we could provide would be useful to other containers). Hopefully, this 
will become clearer as I make my way through the code.

Phil

> 
> 	--- Noel
>