[fedora-java] Handling of EE apis and other multiple implementations

[Stanislav Ochotnicky]

Hi all,

we have been having long-standing issues with multiple implementations
of the same APIs (javax.servlet, javax.servlet.jsp, etc). Namely we
don't handle them at all. They work in Maven through our dependency
mapping, but are not really usable during runtime. 

What I mean is for example several packages requiring javax.servlet
implementation, but in reality they have to pick one of several RPMs we
have. This inevitably leads to bloated installations when users
inevitably end up with more than one implementation installed (and their
deps).

There has always been a solution for this, which is using alternatives
system[1]. We haven't used it, mostly because relatively complicated
nature. So I went looking into simplifying it with rpm macros. Long
story short...this didn't turn out well mostly due to different
implementations needing different things on classpath. 

Ergo: I would like to propose a standardization on naming and use of
java EE APIs.

There are several aspects of this:
 1. We need to chose 1 implementation to serve as "THE" implementation
    for each API. 
 2. That package will get to "Provides: EEAPI". Other packages can stop
    pretenting to provide any EE api :-) They can of course be used
    directly if a package requires something specific.
 3. Since packages will be using "Requires: EEAPI" we can switch
    implementations easily if the need arises (dead project, new major
    version etc.)

Now, I would like to standardize EEAPI naming as well. We have several
versions of this. For example from tomcat.spec:

    Provides: jsp = %{jspspec}
    Provides: jsp22
    ... # other package
    Provides: el_1_0_api = %{epoch}:%{version}-%{release}
    Provides: el_api = %{elspec}
    ... # other package
    Provides: servlet = %{servletspec}
    Provides: servlet6
    Provides: servlet3

So it looks like we are not consistent and I would like to fix that. My
first idea was to have:

    Provides: javax.xml
    ...
    %files
    %{_javadir}/javax.xml.jar # this is symlink

Then I realized JSP is "javax.servlet.jsp", and Servlet API is a
superset so first 2 parts of package name would not be enough there. We
could still have:

    Provides: javax.servlet # in servlet impl
and:
    Provides: javax.servlet.jsp # in jsp impl

To be clear: I want the names to be simple to deduce without going
through spec files, searching with yum (much) etc. The simpler the
better. I would hope Java devs chime in here. What would be the first
thing that came to your mind here?

As for versioning APIs, I am not sure that would be needed. We usually
try to keep packages up to date with latest APIs and packages not
supporting current API can be moved to an older implementation.

How does this sound to you all?


[1] http://fedoraproject.org/wiki/Packaging:Alternatives


-- 
Stanislav Ochotnicky <sochotnicky(a)redhat.com&gt;
Software Engineer - Base Operating Systems Brno

PGP: 7B087241
Red Hat Inc.                               http://cz.redhat.com