Re: [Bodington-developers] Plugin interface

[Alistair Y. <ali...@sm...>]

> I think it's a bit to soon to add it to 2.8
fair enough, yes.

> it would be good if it was available
there's the rub - we don't want to have to merge in tons of stuff =20
when it's uhi specific.

That's where the plugin idea came from:

<plugin ... /> tag in template
Plugin interface and implementation
Configged at runtime.

Can I go back to struts please? I've had enough Facility!

Alistair


On 23 Mar 2006, at 09:58, Colin Tatham wrote:

> Alistair Young wrote:
>> either I'm not getting messages again or it's all gone quiet.
> ;-)
>
>> We'd  like to put org.bodington.plugin and some interfaces in for =20
>> 2.8 so we  can factor out our My Modules but still leave a hook in =20=

>> Facility.
>> This ok with bod.org?
>
> I think it's a bit to soon to add it to 2.8. It's a new approach =20
> and I think it would be sensible to give it more time -- once =20
> something's in a release version it's messy to change. I realise =20
> that doesn't help with your problem. I think MyModules could be =20
> useful to other users, so it would be good if it was available...
>
>
> Colin
>
>
>> On 22 Mar 2006, at 14:32, Alistair Young wrote:
>>> I'm happy to pursue this Adam, if we can agree on how to =20
>>> implement  them
>>> for v1. Lots to think about. We have a concrete use case for a =20
>>> plugin
>>> though, which means minimal merging of Facility.
>>>
>>> The real quesion is whether it's good or bad to let templates =20
>>> call any
>>> class they want. That would free up plugin developers from using  =20=

>>> 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  =20=

>>>> 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 =20
>>>>> the  plugin.
>>>>>
>>>>> public class MinervaHelper extends Facility {
>>>>>    writeModuleLinks( ... ) {
>>>>>      ScreenPlugin ...
>>>>>    }
>>>>> }
>>>>>
>>>>> so a template calls a plugin's facade - MinervaHelper - class  =20
>>>>> 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 =20=

>>>>>>> know
>>>>>>> about
>>>>>>> the class to delegate to it - it has to cast to call methods =20
>>>>>>> etc,
>>>>>>> so it
>>>>>>> has to know about the specific class.
>>>>>>
>>>>>>
>>>>>> At least the delegate methods should be small. This is how I =20
>>>>>> pulled
>>>>>> the
>>>>>> StyleSheet code out on WebLearn HEAD. There is still the =20
>>>>>> problem  that
>>>>>> 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 =20=

>>>>>>> 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/ =20
>>>>>>> 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  =20
>>>>>> refactor code
>>>>>> as you can't be sure without recompiling the templates if a  =20
>>>>>> method is
>>>>>> actually used. At the moment you only have todo this checking =20
>>>>>> 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.
>>>>>>
>>>>>>
>>>>>> --=20
>>>>>>  -- Matthew Buckett, VLE Developer
>>>>>>  -- Learning Technologies Group, Oxford University Computing  =20
>>>>>> Services
>>>>>>  -- Tel: +44 (0)1865 283660 http://www.oucs.ox.ac.uk/ltg/
>>>>>>
>>>>>>
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>>>>>
>>>>>
>>>>>
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>>>>
>>>> --=20
>>>> --=20
>>>> Dr AC Marshall (Bodington developer) OUCS, 13, Banbury Rd. =20
>>>> Oxford.  OX2 6NN
>>>>                Cheese of the month: Smoked Wensleydale
>>>>
>>>>
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>
> --=20
> ____________________________________
> Colin Tatham
> VLE Team
> Oxford University Computing Services
>
> http://www.oucs.ox.ac.uk/ltg/vle/
> http://bodington.org
>
>
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