Re: [Bodington-developers] Plugin interface

[Matthew B. <mat...@ou...>]

Alistair Young wrote:
> damn list - I didn't get the original of this message and it came  from me!
> 
>> Can you create a subclass of Facility?
> 
> I think Facility is a lost cause. We'll wait for Tetra!
> 
> Thinking about maybe specific plugins - ScreenPlugin - writes to 
> screen, DBPlugin - does stuff with the DB. It's just a way to  refactor
> code out of Facility into small packages of functionality  that can
> better be merged etc. Dare I even say, configured at run  time too, ala
> struts/spring (I see cabbages heading my way).
> 
> The basic idea is to have, say, a plugins package in bod:
> 
> org.bodington.plugin
> 
> and have specific interfaces in there:
> 
> ScreenPlugin
> DBPlugin
> 
> public interface ScreenPlugin {
>   public void run(Request req, PrintWriter writer) throws UP;
> }
> 
> not saying that's what they should be called, just to illustrate.
> 
> Template then calls Facility.writeModuleLinks
> 
> Facility.writeModuleLinks (Request req, PrintWriter writer) {
>   ScreenPlugin minerva = (ScreenPlugin)Class.forName
> ("org.bodington.contrib.Minerva");
>   minerva.run(req, writer):
> }

Firstly why do the Class.forName().newInstance() unless you pull this
from a configuration file somewhere. Otherwise just hardwire it as it
makes tracing the code in an IDE much easier.

Secondly checking of modules/plugins should be done at startup time so
that you don't have to test all pages to make sure that you have all the
correct plugins loaded/linked.

> maybe as you say, use a subclass of Facility as a facade for the plugin.
> 
> public class MinervaHelper extends Facility {
>   writeModuleLinks( ... ) {
>     ScreenPlugin ...
>   }
> }
> 
> so a template calls a plugin's facade - MinervaHelper - class instead 
> of Facility
> 
> Can a template call methods in more than one class though? i.e. it 
> might need functionality that's in more than one plugin.

It seems that basically the "Plugin" is just code behind the Facility
facade. Calling it a plugin I think is confusing, traditionally a plugin
is a body of code that can be added/removed at runtime to augment
functionality.

-- 
 -- Matthew Buckett, VLE Developer
 -- Learning Technologies Group, Oxford University Computing Services
 -- Tel: +44 (0)1865 283660 http://www.oucs.ox.ac.uk/ltg/