RE: Attribute question for Commons Digester

[simon <si...@chello.at>]

Hi Jonathan,

The "plugin" mechanism is for something completely different. It allows
an application to process an xml file, and call back into user code when
certain elements are found. This allows "extensible" frameworks to be
written where the basic file format is fixed but users can *at specific
locations* insert their own xml that triggers calls to their own rule
classes.

In your case (special handling of a particular xml attribute), writing a
custom subclass of Rule is the correct solution.

And the digester pattern strings only match elements, not attributes.
So, as you found out, you need to add your custom rule using a pattern
matching the required element, then within your rule pick out whichever
attribute you are actually interested in.

By the way, there are extensive examples on using and extending
Digester. These examples are included in the "source" download bundle,
and can also be browsed directly in the svn repository:
http://svn.apache.org/repos/asf/jakarta/commons/proper/digester/trunk/src/examples/

Regards,

Simon

On Fri, 2007-06-29 at 13:46 +0200, Poulton, Jonathan wrote:
> OK, got it. Configured the rule by doing:
> 
>         digester.addObjectCreate("article", Article.class);
>         digester.addRule("article", new ArticleIdSetRule()); 
> 
> With a class pretty much identical to the skeleton one you posted this
> works just fine, (which is good enough for me), but I'm still not sure
> about how the Plugin mechanism works. Do people usually just create
> their own custom rules instead?
> 
> Thanks very much for the help btw.
> 
> Jon
> 
> -----Original Message-----
> From: jcarman@carmanconsulting.com [mailto:jcarman@carmanconsulting.com]
> On Behalf Of James Carman
> Sent: 29 June 2007 12:22
> To: Jakarta Commons Users List
> Subject: Re: Attribute question for Commons Digester
> 
> Just make a custom rule...
> 
> public class SetIdRule extends Rule
> {
>   public void begin(java.lang.String namespace,       java.lang.String
> name,       org.xml.sax.Attributes attributes)
>   {
>     Article article = ( Article )digester.peek();  // get the thing off
> the top of the "stack"
>     article.setId(cleanUpUnderscore(attributes.getAttribute("id")));
>   }
> }
> 
> That's off the top of my head, so the method names might have been
> changed to protect the innocent. :)
> 
> Then, add it to your Digester using the addRule() method
> 
> On 6/29/07, Poulton, Jonathan <jp...@verisign.com> wrote:
> > Also, does the plugin class need to implement a specific class? It 
> > doesn't look that way in the examples, and there doesn't appear to be 
> > any way to get the Digester to call a specific method in the plugin 
> > class.
> >
> > I have the feeling I have misunderstood something here..
> >
> > -----Original Message-----
> > From: jcarman@carmanconsulting.com 
> > [mailto:jcarman@carmanconsulting.com]
> > On Behalf Of James Carman
> > Sent: 29 June 2007 11:59
> > To: Jakarta Commons Users List
> > Subject: Re: Attribute question for Commons Digester
> >
> > Yeah, I didn't notice the "_" (or read the rest of the request).  
> > You'll need a custom rule here to convert that value, otherwise 
> > SetProperties would work (and you don't need to specify "id"/"id" 
> > because it'll match the properties to the attributes if they match 
> > exactly).  Why the underscore anyway?
> >
> > On 6/29/07, Poulton, Jonathan <jp...@verisign.com> wrote:
> > >
> > > You mean:
> > >
> > >         digester.addObjectCreate("article", Article.class);
> > >         digester.addSetProperties("article", "id", "id");
> > >
> > > Yup. I've tried that. The actual value of the id field in the XML 
> > > "_1234" is ignored and "0" is set on the Article id field instead. I
> 
> > > assume that this is because of the underscore in the id field.
> > >
> > > -----Original Message-----
> > > From: jcarman@carmanconsulting.com
> > > [mailto:jcarman@carmanconsulting.com]
> > > On Behalf Of James Carman
> > > Sent: 29 June 2007 11:48
> > > To: Jakarta Commons Users List
> > > Subject: Re: Attribute question for Commons Digester
> > >
> > > Have you tried an ObjectCreate followed by a SetProperties?
> > >
> > > On 6/29/07, Poulton, Jonathan <jp...@verisign.com> wrote:
> > > >
> > > > Surely someone has done this before?
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: Poulton, Jonathan [mailto:jpoulton@verisign.com]
> > > > Sent: 28 June 2007 17:41
> > > > To: commons-user@jakarta.apache.org
> > > > Subject: Digester problem
> > > >
> > > > Hi there,
> > > > I've tried finding a solution to what I think should be quite a 
> > > > simple
> > >
> > > > problem using the Commons Digester, but the tutorials I can find 
> > > > on the subject only really cover the basics and aren't of any
> help.
> > > >
> > > > Given an XML fragment like the following:
> > > >
> > > > <article id="_1234">
> > > >     <text>...</text>
> > > > </article>
> > > >
> > > > I need the Digester to call a method on an Article class, with the
> 
> > > > following signiture:
> > > >
> > > > public void setId(long id);
> > > >
> > > > In other words I just need a Rule that will fire for an XML "id"
> > > > attribute, and remove an underscore from the front of a String 
> > > > before converting it to a long, and calling the appropriate
> method.
> > > >
> > > > I realise that this will require some kind of custom class to chop
> 
> > > > up the String, but the pattern you apply to matching the rule
> > > > ("article/id") appears to refer to a nested id element, rather 
> > > > than an
> > >
> > > > id attribute.
> > > >
> > > > I can't seem to find an example of this anywhere. All the custom 
> > > > rules
> > >
> > > > examples appear to refer to nested elements. Any suggestions? Have
> 
> > > > I
> >
> > > > missed something in the API?
> > > >
> > > > Cheers
> > > >
> > > > Jon
> > > >
> > > >
> > > >
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