RE: FactoryCreateRule Example?

[Greg McCreath]

Robert,

That'll get me on my way ...

Many thanks.

Greg.

-----Original Message-----
From: robert burrell donkin [mailto:[EMAIL PROTECTED]]
Sent: 21 March 2002 20:59
To: Jakarta Commons Developers List
Subject: Re: FactoryCreateRule Example?


On Thursday, March 21, 2002, at 04:16 PM, Greg McCreath wrote:

hi greg

> Can anyone point me to where I might might find one of the above.

you can find what documentation there is in the 
org.apache.commons.digester package java doc comments.

(documentation patches will be gratefully received.)

> I want to have an object created using Digester, but the object will have
> two non no-argument constructors, and I want both of them to be recognised
> from the XML. As an example of what I want  ...
>
> < commsMessageFormatter class="MyClass" />
>
> or
>
> < commsMessageFormatter class="MyClass" protocolType="ISOxxxx" />
>
> or
>
> < commsMessageFormatter class="MyClass" protocolType="ISOxxxx"
> protocolVersion="1.0" />

(i'm going to assume that you're happy(/ier) with the pattern matching 
rules and talk about using FactoryCreateRule only.)

in order to use a FactoryCreateRule you need to make a 
ObjectCreationFactory implementation. you'll probably want to extend 
AbstractObjectCreationFactory and just override the createObject method.

createObject has the element's attributes passed in. use these to decide 
which constructor to call.

i quite often do is use an anonymous class so it'd probably go something 
like:

digester.addFactoryCreate(
     "/root/alpha",
     new AbstractObjectCreationFactory() {
          public Object createObject(Attributes attributes) {
              if (attributes.getLength() == 1) {
                  // return object created with single parameter constructor
                  ...
              }

              if (attributes.getLength() == 2) {
                  // return object created with double parameter constructor
                  ...
              }

              ...
          }
     }
}

hope that's enough to get you started.

- robert


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