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From Christian Schneider <ch...@die-schneider.net>
Subject Re: Discuss: Use DS for karaf bundles
Date Thu, 17 Mar 2016 16:06:00 GMT
I see the issue for blueprint as it is quite heavy weight.
Scr on the other hand is just one bundle.

Christian

On 17.03.2016 16:58, Morgan wrote:
> I only see one problem.
> JB wants to keep a normal/default distro where scr could have a place 
> in the distro and also a minimal distro without scr so I don't know 
> how you would deal with that?
>
> On 2016-03-17 16:43, Christian Schneider wrote:
>> 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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