"Robert Leland" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > Replyied Inline. > > Paananen, Tero wrote: > > >[this is in response to Robert Leland's reply to my > > post on the struts-user list griping about the > > (un)extensibility of custom tags] > > > > > > > >>>My #1 pet peeve about custom taglibs are that almost > >>>none of them have been designed with extensibility in > >>>mind. This includes all the Struts tags that I've had > >>>to tinker with. > >>> > >>>Extending them basically means, more or less, > >>>copy-and-pasteing all the existing code into your new > >>>taglib, then customizing the behavior to meet your > >>>needs. > >>> > >>> > >>Tero: > >> > >> Your insight into how the Struts Tags can be made > >>more Modular so they can be extended easier would be very > >>valuable and welcome.I encourage you can bring the issue > >>up on the struts-dev list. > >> > >> > > > >Robert, > > > >>From what I've seen most custom tags seem to have been > >implemented as one big doStartTag() or doEndTag(). The > >entire implementation of the tag is in that one method. > > > >In order to modify the behavior, more often than not, > >the only way to do this, is to completely rewrite that > >method by copy-and-pasting the old implementation into > >your new tag, modify it slightly and be done with it. > >The only reuse comes with the getters and setters for > >the tag's properties. > > > >This approach to "extending" breaks the minute a new > >release of your "base" tag changes significantly. You > >either have to redo your extended tag based on the new > >release or leave your extended tag as is, and potentially > >leave bugs in that were fixed in the new release. > > > >I've had some limited success with tags that implement > >doStartTag() (and/or doEndTag() in more discreet steps: > > > > // method names and (non-existing) return types > > // purely illustrative > > public int doStartTag() throws JspException { > > doStart(); > > doStep1(); > > doStep2(); > > doEnd(); > > } > > > >This way you can overload only the method that deals > >with whatever you need to modify and leave everything > >else as is. > > > >If you also had pre- and post-processing methods for > >every discreet step in the "process", you'd have even > >more flexibility: > > > > // method names and (non-existing) return types > > // purely illustrative > > private String doStep1() { > > preDoStep1(); > > > > // step 1 implementation here > > > > postDoStep1(); > > } > > > >Hopefully you see where I'm going with this. The pre- > >and post-processing methods could be implemented to > >skip, ignore, modify, etc. the implementation of the > >real method. > > > >I haven't done anything like this with custom tags > >myself, but I've used a few products (ATG Dynamo comes > >to mind first) that use this sort of architecture in > >the entire application, and it's extremely flexible. > > > >I realize that doing something like this would probably > >have a performance impact and would most likely be overkill > >for everyone but that one screwed up developer that needs > >to modify every tag he gets his hands on, but as far as > >extensibility goes, something like this would greatly > >improve on how custom tags can be extended, IMHO. > > > I doubt there would many any notiable impact on performance.
I agree *iff* we're careful about the way it's done. Some of the method calls will probably go away anyway if the code is automatically inlined, so I don't believe method invocation would be the issue. However, looking at FormTag right now, I see several methods that build up strings in StringBuffer instances and convert those to String instances so that they can then be appended to a StringBuffer. All that string processing can mount up and cost you in the long run, where it would be much more efficient to pass the original StringBuffer to those methods so that they can append what they need, without requiring the creation, copying and destruction of multiple StringBuffer and String instances in between. -- Martin Cooper > > > > >I'm sure people on the list who have far more experience > >than I do with writing taglibs, and application architectures > >in general, will see lot of things wrong with this approach > >and can come up with something better, but as someone who > >has had to extend a somewhat large number of custom tags > >(Struts and otherwise), I'm completely fed up with the > >copy-and-paste codeing I'm forced to do right now. > > > I feel your pain as one ex-U.S. President once said. > > >What say ye, oh Struts gods (and goddesses)? :) > > > I agree totally, at the level were currenrly arguing, I dare anyone to > disagree ! > A good way to tackle this is Use Case by Use Case, to avoid talking in > general terms. > 1) What specific tags have you or do you want to modify the behaviour of. > 2) What level of granularity makes sense. > 3) Do we use simple overriding, or publish/subscribe or Decorator > Pattern, others. > I would start off by recommending the Decorator pattern. I believe > this is what > David Karr did when adding JSTL functionality to Struts. > > > > -TPP > > > > > -Rob > > > >--------------------------------------------------------------------- > >To unsubscribe, e-mail: [EMAIL PROTECTED] > >For additional commands, e-mail: [EMAIL PROTECTED] > > > > > > > > > > > > > -- > Robert Leland [EMAIL PROTECTED] > ------------------------------------------ > Java, J2EE, Struts, Web Application Development > > 804 N. Kenmore Street +01-703-525-3580 > Arlington VA 22201 > > --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
