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From "James Strachan" <james_strac...@yahoo.co.uk>
Subject Re: [BeanUtils] PropertyUtils and DynaBeans (getPropertyDescriptors)
Date Tue, 16 Apr 2002 03:40:39 GMT
Hi Stephen

I did think a standard wrapper around the Introspector would be a good idea,
especially because the standard introspection mechanism cannot support
DynaBeans, since the Introspector just takes a Class rather than the
instance, and its the instance data of a DynaBean (its DynaClass) which
defines its properties etc.

Though I guess the static methods of PropertyUtils actually are this
wrapper. e.g.

PropertyUtils.getPropertyDescriptors(bean);
PropertyUtils.getMappedPropertyDescriptors(bean);

Also DynaBeans right now can't support beans PropertyDescriptors, presumably
because its not possible to implement read & write Methods. Unfortunately
Method is final so we couldn't create a method proxy that the getter would
call DynaBean.get( "someName" ) and similar for the setter method. So it
wouldn't be possible to make DynaBeans act like regular beans. (Shame!).

Though maybe another idea is to treat everything as a DynaBean. Any regular
bean can be wrapped pretty easily as a DynaBean.

e.g.

Object bean = ...;
DynaBean dynaBean = new WrapDynaBean( bean );

So maybe DyanBean could actually become the wrapper around the introspector?
This approach would then supports beans, DynaBeans, mapped properties and so
forth in a simple consistent manner.  Also the DynaBean / DynaClass is alot
easier than working from the Introspector directly, no need to mess with
arrays of PropertyDescriptors et al. WrapDynaClass maintains a Map of
PropertyDescriptors so its an efficient way of working with beans.

Also WrapDynaClass instances are cached so all in all the approach of using
DynaBeans all the time as a bean/Introspector replacement seems like a good
idea. So if you're not being typesafe, using DynaBeans seems like the way to
go. DynaBeans rock ;-)

James
----- Original Message -----
From: "Stephen Colebourne" <scolebourne@eurobell.co.uk>
To: "Jakarta Commons Developers List" <commons-dev@jakarta.apache.org>
Sent: Saturday, April 13, 2002 2:42 PM
Subject: Re: [BeanUtils] PropertyUtils and DynaBeans
(getPropertyDescriptors)


> What I am really getting at is whether it would be worth having the
ability
> in beanutils to replace Introspector. What I have in mind (borrowed from a
> James Strachan idea)  is a new class, lets say  IntrospectUtils  that can
be
> used instead of Introspector. The only method of relevance is
> getBeanInfo(Class). By default, IntrospectUtils would simply call on to
> Introspector.
>
> Then, we would define a new beanutils interface  BeanInfoProvider  that
has
> a getBeanInfo(Class) method. Instances of BeanInfoProvider could be
> registered with IntrospectUtils. Calling getBeanInfo() on IntrospectUtils
> would then call each registered provider in turn. If the provider returned
> BeanInfo then that would be returned, else Introspector would be used.
>
> An implementation of BeanInfoProvider could then be added for DynaBeans.
> This could enable parts of PropertyUtils to be simplified, treating
> DynaBeans the same as regular beans. (It would also allow the joda project
> to interoperate with PropertyUtils :). There could even be a full
> reimplementation of Introspector for normal beans to create and return
> MappedPDs when it spots them. (and ListPDs as well...).
>
> I guess this comes down in part to the goals of beanutils. If it is
strictly
> following the beans spec then this isn't appropriate. But then with
MappedPD
> and DynaBeans IMHO the project has already strayed beyond the original
> concept of reflection helper methods.
>
> Stephen
>
> > From what I understand, the property descriptor really handles the
> > straight invocation of a bean property, not getting a hold of a
> > collection and using it. For example, the IndexedPropertyDescriptor
> > won't get back the Object[] and then get the object from the index, it
> > only takes the "Object getMyProperty(index)" style property methods.
> >
> > If you look at the indexed part of PropertyUtils, handling the Object[]
> > is the special case outside of the descriptor. Through this we're also
> > getting an item from a java.util.List implementation.
> >
> > Similar to all that is the MappedPropertyDescriptor.
> >
> > PropertyUtils/BeanUtils was apparently meant to be an implementation of
> > the Bean spec (though I don't see mapped properties in the bean spec :),
> > and to carry it out seems that these collection type uses need to be
> > manually handled. Use PropertyUtils and you'll get at your Lists.
> >
> > Arron.
> >
> > Stephen Colebourne wrote:
> >
> > >I've just spent the evening trying to figure out the property
descriptor
> > >classes myself. For the joda project I wanted to return a BeanInfo
> > >specifying a description of the bean. But it seems to be a bit tricky.
> > >
> > >PropertyDescriptor is OK for my needs (just about)
> > >IndexedPropertyDesciptor is not much use as it only covers arrays, not
> Lists
> > >MappedPropertyDescriptor seems to be of limited use. It is picked up
from
> > >BeanInfo, but does not include the Map getXxxMap() type method as Arron
> > >noted.
> > >
> > >Nothing really handles Lists, and I also noted that DynaBeans don't use
> > >PropertyDescriptors.
> > >
> > >One solution would be for beanutils to have a ListPropertyDescriptor
that
> > >copes with getXxxList() and getXxx(int). Plus extending
> > >MappedPropertyDescriptor to cover getXxxMap().
> > >
> > >This all seems hard work however. The beans spec is pretty outdated
these
> > >days (thats why I started joda really). My question is whether these
> > >extended (ie. java.beans) PropertyDescriptor classes really are that
> > >useful - can they really be used as general purpose classes without
> writing
> > >a full replacement to java.beans.Introspector?
> > >
> >
> >
> >
> >
> > --
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> >
> >
>
>
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