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From Dmitri Plotnikov <dmi...@apache.org>
Subject Re: [reflect] Proposal: (WAS [BeanUtils] etc...)
Date Sun, 16 Jun 2002 19:15:32 GMT
Ola,

Perhaps I misunderstood what the proposal was all about.  My understanding
was that it was after introspection rather than pure reflection.  When I
hear the word "reflection", the list of features that comes to my mind is:

1. List of methods
2. List of constructors
3. List of fields
4. List of inner classes

And that's about it - all of this is basically done by the JVM itself.
Sure, we can put some veneer over it - but I thought this proposal called
for something more.

The word "introspection" is one level above reflection: beans, bean
properties etc.  These may be implemented using reflection or not.  This is
where the diversity begins.  Pretty much everybody supports JavaBeans.  But
then on top of that we all add our extensions: BeanUtils support DynaClass,
JXPath has JXPathBeanInfo, etc.  We are all expanding the notion of a Bean
beyond the official JavaBean specification.  Strictly speaking, even Ant
with its mapping of "foobar" to "getFooBar" is extending the specification.

There is a layer above introspection, which is abstract models and mapping
those models to Java artifacts.  For example, there is a JSR that maps UML
to EJB.  IMO, that stuff is much too abstract for our purposes. We don't
want to end up with something like MOF, which is complex to the point of
being almost esoteric.

I am not convinced we can do anything about Java Reflection - it is built
natively into the JVM.  Introspection though is a different matter.

- Dmitri


> >The multitude of potential users of this component is
> >huge, they all have
> >current solutions and they all have some peculiarities about them. For
this
> >new component to be successful, we will need to address all of those
> >requirements, which calls for an abstract, configurable and customizable
> >architecture.
>
> I don\'t agree. Well, of course there are many users that do a lot of
stuff in their reflection/introspection packages.
>
> But IMO reflect should be a mere utility for easy use of reflection
(reducing complexity and awkwardness in java.lang.reflect). Other cool
things (like automatic configuration of beans from command line or config
files) do belong in other packages (both examples above should go in a
Configuration framework?).
>
> Those are _users_ of reflection, they don\'t faciliate reflection in
themselves. This doesn\'t call for plugable architectures, and if we end up
with it I believe that we have over-engineered them and missed a clean
separation of concerns.
>
> I think of a Reflection class with static methods like
>
> Reflection.set( Object bean, String propertyName, Object value);
>
> Object o = Reflection.get( Object bean, String propertyName);
>
> Reflection.add( Object bean, String propertyName, Object value);
>
> Reflection.put( Object bean, String propertyName, Object key, Object
value);
>
> Reflection.set( Object bean, String propertyName, int index, Object
value);
>
> Object result = Reflection.call( Object bean, String methodName, Object []
parameterValues);
>
> The internals of a Reflection class could very well use a plugable
framework for insertion of new handy methods and cached lookup of reflection
Method objects (like all getters in a class etc), and some of this
functionality should probably be pluggable (for people to insert new
bean-like naming conventions, maybe using Predicate on methods).
>
> But main functionality exposed as handy methods.
>
> /O
>
> --------------------
> ola.berg@arkitema.se
> 0733 - 99 99 17
>
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