Re: [Htmlparser-developer] Re: Adding methods to Tag
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Re: [Htmlparser-developer] Re: Adding methods to Tag
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From: Joshua K. <jo...@in...> - 2003-08-30 23:28:52
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Derrick,
Thanks for sharing this email. I have some opinions on this -- can't
email them at the moment. Will do soon...
regards
jk
Derrick Oswald wrote:
> Chris,
>
> I'm opening this up to a wider audience, because it may have been solved
> before, or might be of interest to others with the same problem.
>
> The basic problem is how to add functionality like supportsColor() to
> base classes, like Tag, without recompiling the whole class heirarchy.
>
> One way would be to join the htmlparser project as a developer and just
> add it, if it's germane to others besides yourself. If it's not, then a
> bolt-on is needed.
>
> One way to handle this problem is a 'Factory' mechanism. A
> 'deep-in-the-bowels' class would ask the 'factory' for a tag, i.e.
> factory.makeTag ("Form"). So you would wedge your own factory in there.
> Choosing the factory is usually done with a Class.forName() where the
> string specifying the class comes from a configuration setting. With
> some design effort, we should be able to come up with a definition for a
> factory class and a suitable set of interfaces which the whole project
> would be refactored to use, i.e. the IFormTag interface extends the
> ICompositeTag interface and adds form related methods; the ICompositeTag
> interface extends the IBaseTag interface and adds child accessors; and
> nothing references FormTag directly except the factory.
>
> So then there is the problem of your factory supplying your special tag
> that implements IFormTag *and* IColorSupport when makeTag ("Form") is
> called. Most of what you need is already written in FormTag, you just
> need to add a couple of methods. I think this is where dynamic proxies
> come in: http://java.sun.com/j2se/1.3/docs/guide/reflection/proxy.html.
> The InvocationHandler would determine if the target method comes from
> IColorSupport, and if so perform the needful directly. Otherwise it
> would delegate to the wrapped tag object. This means the whole
> htmlparser project shuttles wrapped tag objects around and doesn't know
> it, till they bubble up to your code where you cast them to an
> IColorSupport and invoke the supportsColor() method:
>
> Parser.setTagFactory ("ChrisBirdFactory");
> Parser parser = new Parser (url);
> parser.registerScanners ();
> for (NodeIterator e = parser.elements (); e.hasMoreNodes (); )
> {
> Node node = e.nextNode ();
> if (node instanceof Tag) // I presume all tags, but not nodes,
> support IColorSupport
> ((IColorSupport)node).supportsColor ();
> }
>
> Derrick
>
> Christopher Bird wrote:
>
>> Thanks for the reply, that is my dilemma.
>>
>> I am an old Smalltalk programmer from years gone by and have always
>> used what is sometimes called responsibility driven development. So
>> (at least in my head), the responsibilty for knowing that a tag
>> supports color or BG color is the tag's responsibilty, and not the
>> responsibility of some agent acting on the tag.
>>
>> The trouble with that style of development, especially for "packaged"
>> software is that you(I) find yourself(myself) in a bind like this one.
>>
>> Indeed I had to recompile the whole package! But since I have the
>> source in my project (to help me learn the intricacies of certain
>> behaviors - especially the creation of handlers for very complex tags)
>> that was no big deal for me. However now I am in violation of protocol
>> for OpenSource, I am sure.
>>
>> This really gets to the crux of OOness and Open Source development.
>> When there are requirements for classes high in the inheritance
>> hierarchy and they do "rightfully" belong there how does one get them
>> there - short term to overcome a specific issue, and long term as part
>> of the overall release cycle of the product.
>>
>> I am probably not the first to wonder this!
>>
>> BTW, I love the implementation. It took some mind-bending to get used
>> to it at first - again separating the responsibilities out so I can
>> factor my solutions properly was initialy a challenge, but I have
>> become very productive.
>>
>> Thank you so much for an excellent piece of technology.
>>
>> Regards
>>
>> Chris
>>
>>
>>> From: Derrick Oswald <Der...@ro...>
>>> To: Christopher Bird <se...@us...>
>>> Subject: Re: Adding methods to Tag
>>> Date: Fri, 29 Aug 2003 07:41:08 -0400
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>>> preview: Chris, It's unclear how your ChrisTag method would
>>> workwithout recompiling the whole package. The Tag class
>>> extendsAbstractNode, so presumably ChrisTag would extend AbstractNode
>>> and addthe methods you want, then Tag would extend ChrisTag. You
>>> would stillneed to 'fix' each new release by doctoring Tag. [...]
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>>>
>>> Chris,
>>>
>>> It's unclear how your ChrisTag method would work without recompiling
>>> the whole package. The Tag class extends AbstractNode, so presumably
>>> ChrisTag would extend AbstractNode and add the methods you want, then
>>> Tag would extend ChrisTag. You would still need to 'fix' each new
>>> release by doctoring Tag.
>>>
>>> The best way is probably to have a class external to everything with
>>> the static methods needed (see Tag.breaksFlow() for example code):
>>> class ColorKnowledge {
>>> public static boolean supportsColor (Node node)
>>> { return
>>> (listofNodesSupportingForegroundColor.contains(node.getText().toUpperCase()));}
>>>
>>> ...
>>>
>>> If it's generic enough, submit it and we'll add it to Node.
>>>
>>> Derrick
>>>
>>> Christopher Bird wrote:
>>>
>>>> I am new to using OpenSource code. I have found it very
>>>>
>>>> helpful, and am using the HTMLParser for a number of
>>>>
>>>> purposes.
>>>>
>>>>
>>>>
>>>> I am wanting to add some code to Tag - especially the
>>>>
>>>> following two methods:
>>>>
>>>>
>>>>
>>>> public boolean supportsColor()
>>>>
>>>> /* returns true iff the color attribute is valid for this tag
>>>>
>>>>
>>>>
>>>> public boolean supportsBGColor ()
>>>>
>>>>
>>>>
>>>> /* Returns true iff the bgColor attribute is valid for this tag
>>>>
>>>>
>>>>
>>>> I would be happy if you guys were to add that, but failing
>>>>
>>>> that what is the process if I have to do it myself? There may
>>>>
>>>> be a bunch of other things that I will want to add to Tag -
>>>>
>>>> for handling some of my own custom behaviors.
>>>>
>>>>
>>>>
>>>> I can see a couple of ways of doing this (none pretty). One is
>>>>
>>>> to create a new ChrisTag superclass and change Tag's
>>>>
>>>> implements clause to implements ChrisTag. I can then define
>>>>
>>>> my methods there. Of course the community doesn't get the
>>>>
>>>> benefit (? dubious in some cases, I fear) of my additions.
>>>>
>>>>
>>>>
>>>> The other obvious way is simply to add the methods to Tag
>>>>
>>>> itself. I am not wild about doing that either because as I
>>>>
>>>> download new editions of HTMLParser, my changes get lost -
>>>>
>>>> especially since I am a solo practitioner at the moment and
>>>>
>>>> am not using a source code management system.
>>>>
>>>>
>>>>
>>>> Any assistance would be gratefully appreciated - both to the
>>>>
>>>> short term (immediate) problem and to the general question.
>>>>
>>>>
>>>>
>>>> Thanks in advance
>>>>
>>>>
>>>>
>>>> Chris Bird
>>>>
>>>>
>
>
>
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