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From Christian Schneider <ch...@die-schneider.net>
Subject Discuss: Use DS for karaf bundles
Date Thu, 17 Mar 2016 15:43:51 GMT
We currently use some custom Activator base classes to wire the karaf 
bundles. The goal of this was to avoid depending on blueprint
as it is a quite heavy dependency and makes it harder to use a different 
blueprint impl or version.

There are some problems with this approach though:
- It makes it harder for new people to understand what we are doing
- The custom code is more error prone than a proven framework

So I propose to switch our own bundles to use DS to expose and wire 
services.

There are some advantages:
- The DS annotation approach is easier to understand and more self 
documenting than the custom code
- We get rid of the classes in util for the custom code
- The scr commands help diagnose problems

The main cost is that we need to always install the felix scr bundle.

To prove that it can work I switched bundle core in a branch 
https://github.com/apache/karaf/tree/EXPERIMENTAL_DS .
The DS based code works quite nicely.

Btw. I found a small problem with our shell command extender. It only 
seems to work on all commands or none. If there is any required service 
missing then none of the commands is installed.
This made it hard for me to diagnose problems as I was missing all 
bundle commands ;-)
So while working on the switch I thought about two improvements to the 
extender:
1. Work on each command individually. So each command can activate as 
soon as the deps are met
2. Provide a service and commands to diagnose problems like the scr commands

Christian

-- 
Christian Schneider
http://www.liquid-reality.de

Open Source Architect
http://www.talend.com


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