Re: [Bodington-developers] Plugin interface

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I'm happy to pursue this Adam, if we can agree on how to implement them
for v1. Lots to think about. We have a concrete use case for a plugin
though, which means minimal merging of Facility.

The real quesion is whether it's good or bad to let templates call any
class they want. That would free up plugin developers from using Facility=
.

--=20
Alistair Young
Senior Software Engineer
UHI@Sabhal M=F2r Ostaig
Isle of Skye
Scotland

> Plugins are something that Boding desparately needs, perhaps we should
> dedicate
> some time to work with Al after our new WebLearn release?
>
> adam
>
> In message <7A5...@sm...>
> bod...@li... writes:
>> 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 =3D (ScreenPlugin)Class.forName
>> ("org.bodington.contrib.Minerva");
>>    minerva.run(req, writer):
>> }
>>
>> maybe as you say, use a subclass of Facility as a facade for the plugi=
n.
>>
>> 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.
>>
>> Alistair
>>
>>
>>
>> On 22 Mar 2006, at 10:17, Matthew Buckett wrote:
>>
>> > Alistair Young wrote:
>> >> Bodders, I've been delurked, damn, to ask opinions.
>> >>
>> >> We have a requirement for My Modules, which is specific to us so
>> >> we don't
>> >> want to pollute Facility. However, a template must call facility
>> >> to get it
>> >> to write stuff to the screen.
>> >
>> > Can you create a subclass of Facility?
>> >
>> >> The writing is delegated to another class which is currently in
>> >> org.bodington.contrib on our HEAD but Facility still needs to know
>> >> about
>> >> the class to delegate to it - it has to cast to call methods etc,
>> >> so it
>> >> has to know about the specific class.
>> >
>> > At least the delegate methods should be small. This is how I pulled
>> > the
>> > StyleSheet code out on WebLearn HEAD. There is still the problem tha=
t
>> > Facility ends up with 100s of method calls.
>> >
>> >> A better way would be to define, e.g.
>> >>
>> >> package org.bodington.contrib;
>> >>
>> >> public interface Plugin {
>> >>   public void run(Request req, PrintWriter writer) throws
>> >> SomeOrribleException;
>> >> }
>> >>
>> >> then our class could implement Plugin and Facility would only have
>> >> to load
>> >> it via Class.forName as a Plugin and call it's run method.
>> >
>> > Can you explain the call graph a little more.
>> >
>> >> It reduces the code in Facility and brings a sort of IOC/dependancy
>> >> injection to Facility.
>> >>
>> >> What would be even better though is allowing templates to call
>> >> whatever
>> >> class they wanted and not just Facility or a subclass thereof.
>> >
>> > I added support for making static calls from template but I don't
>> > think
>> > this is a good move as then it becomes move difficult to refactor co=
de
>> > as you can't be sure without recompiling the templates if a method i=
s
>> > actually used. At the moment you only have todo this checking when
>> > working with public methods in Facility. It also means that the
>> > idea of
>> > linking a template with a Facility in a configuration file breaks
>> > down.
>> >
>> >
>> > --
>> >  -- Matthew Buckett, VLE Developer
>> >  -- Learning Technologies Group, Oxford University Computing Service=
s
>> >  -- Tel: +44 (0)1865 283660 http://www.oucs.ox.ac.uk/ltg/
>> >
>> >
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>> > Bod...@li...
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>>
>>
>>
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>
> --
> --
> Dr AC Marshall (Bodington developer) OUCS, 13, Banbury Rd. Oxford. OX2 =
6NN
>                Cheese of the month: Smoked Wensleydale
>
>
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