[jsr342-experts] Across the board DD property substitution

From: Jason T. Greene <jason.greene_at_redhat.com>
Date: Thu, 19 Apr 2012 11:16:11 -0500

This is somewhat related to the password aliasing discussion awhile back.

One popular feature we have had some support for in many of the JBoss AS
vendor descriptors is the ability to reference system properties that
get resolved at deployment. This is useful for prod/staging/test
differentiation, and also running an application in a cloud environment.

I really think we should consider enabling this in all spec descriptors
as well for EE7. The problem with relying on vendor descriptors to do
this is that you have to maintain a duplicate structure just to use
property replacement which becomes a maintenance burden (especially now
that these spec descriptors are less frequently needed due to EE5 and
EE6 enhancements). Descriptor overrides are even worse because you have
to maintain a duplicate for every distinct environment an application
can run on.

Along with various benefits like controlling environmental values (ip
addresses etc) this leads to other interesting capabilities, like the
power to control the active @Alternative in CDI using a property.

There is of course a compatibility issue to deal with that requires
thought. Someone might have used system properties as an actual value
string, and resolve it in their code to work around the lack of this
feature (the TCK does this for example). One solution could be to
introduce a common attribute/element to every descriptor enabling it.

Another consideration is supporting multiple sources (system props,
container props, password stores, etc). We could leave this up to the
vendor, or define a common set.


Jason T. Greene
JBoss AS Lead / EAP Platform Architect
JBoss, a division of Red Hat