Supporting application specific variables
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Key: ARIES-712
URL: https://issues.apache.org/jira/browse/ARIES-712
Project: Aries
Issue Type: Brainstorming
Components: Blueprint, JPA
Reporter: Balazs Zsoldos
Starting with OSGI I met a problem that I could not solve in any general way
till now: I would like to use the same module from different "applications" but
with slightly different configuration.
More specifically: I would like to create a bundle that contains persistence
services. I would like to use this bundle from several applications but with
different database which means I would like to use different persistence units.
Currently I can use <jpa:context ...> to define a container managed
EntityManager in my service beans. It is a very nice way however I cannot make
the unit-name dynamic in this tag. My database schema is used as part of many
different application (schema to handle permissions).
I am thinking since days and it seems to me that a solution like the following
would solve my problem:
- Having a service called ApplicationService. This has methods:
setApplicationParameter(String paramName, Object value);
getApplicationParameter... The parameters of the current application are stored
in a thread local variable.
- Having a new blueprint tag: <app:parameter name="someName" ref="..." />. This
tag does the followings:
- Works the same as PropertyPlaceHolderConfigurer to eliminate possible
duplicate configurations
- Wraps all services in the way that when a function is called on them the
application parameters are set and when it returns the olda application
parameters are re-set (if there were any)
- Having a possibility inside <jpa:context .../> where the unit-name comes from
application parameters. With that the bundle is re-usable while many different
applications can use it with their database.
- Better would be not to define unit-name but entity manager factory itself as
an application parameter as it makes it necessary that the persistence unit
exists when the bundle that contains the application parameters is deployed.
Note that I do not talk here about the Aries EBA solution. I would like to have
as less jars in my JVM as it is possible. Please let me know if you like this
kind of approach as in that case I will check if I have time to implement it.
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