Re: [Springframework-developer] Reworked root/child bean definition concept

[Rod J. <rod...@in...>]

I like this. Actually the Interface21 framework had something =

closer to this (although parent class couldn't be changed). =

It's certainly useful for templating. =


For example, this might be used to set up a ProxyFactoryBean =

for repeated use, allowing subclasses to set target and =

(optionally) override advice.

Capturing such reused information in on=
e place is definitely =

desirable.

Rod

---- Original message ----
>Date: Thu, 24 Jun 2004=
 16:43:44 +0200
>From: j=FCrgen h=F6ller [werk3AT] <juergen.hoeller@wer=
k3at.com>  =

>Subject: [Springframework-developer] Reworked root/child =

bean definition concept  =

>To: <spr...@li...>
>
>I've just co=
mmitted a fairly significant reworking of our =

root/child bean definition concept: A child can now inherit =

respectively override virtually any attributes from a parent, =

not just bean property values and the singleton flag. From =

the new ChildBeanDefinition javadoc:
>
> * <p>Will use the bean class =
of the parent if none =

specified, but can
> * also override it. In the latter case, the child =
bean =

class must be
> * compatible with the parent, i.e. accept the parent's =
=

property values
> * and constructor argument values, if any.
> *
> * =
<p>A child bean definition will inherit constructor =

argument values,
> * property values and method overrides from the pare=
nt, =

with the option
> * to add new values. If init method, destroy method a=
nd/or =

static factory
> * method are specified, they will override the =

corresponding parent settings.
> *
> * <p>The remaining settings will =
<i>always</i> be taken =

from the child definition:
> * depends on, autowire mode, dependency ch=
eck, singleton, =

lazy init.
>
>Everything that worked before still works; it should be =
=

fully backward compatible. Formerly, this mechanism has =

mainly been used for view definitions; there's just a much =

wider range of usage scenarios now, for example:
>
>  <bean id=3D"inhe=
ritedTestBean" =

class=3D"org.springframework.beans.TestBean">
>    <property name=3D"na=
me"><value>parent</value></property>
>    <property name=3D"age"><value=
>1</value></property>
>  </bean>
>	=

>  <bean id=3D"inheritsWithDifferentClass" =

class=3D"org.springframework.beans.DerivedTestBean"
>      parent=3D"in=
heritedTestBean" init-method=3D"initialize">
>    <property name=3D"nam=
e"><value>override</value></property>
>    <!-- age should inherit valu=
e of 1 from parent -->
>  </bean>
>
>The child class above uses a dif=
ferent bean class and init =

method, but still inherits the property values from the =

parent. Alternatively, the parent can even omit the bean =

class completely, simply specifying common properties for =

children:
>
>  <bean id=3D"inheritedTestBeanWithoutClass">
>    <prop=
erty name=3D"name"><value>parent</value></property>
>    <property name=
=3D"age"><value>1</value></property>
>  </bean>
>
>  <bean id=3D"inhe=
ritsWithClass" =

class=3D"org.springframework.beans.DerivedTestBean"
>      parent=3D"in=
heritedTestBeanWithoutClass" init-
method=3D"initialize">
>    <proper=
ty name=3D"name"><value>override</value></property>
>    <!-- age shoul=
d inherit value of 1 from parent -->
>  </bean>
>
>Of course, such a =
parent bean cannot get instantiated on its =

own: It's just a template that serves as parent definition =

for children. preInstantiateSingletons will ignore such beans =

without class and parent completely.
>
>I'm aware that this is a signi=
ficant change in concept, but =

I've experienced repeatedly that this is what users expect it =

work like - being surprised that all they could do was =

overriding bean property values. A colleague of mine has a =

current use case that I've changed this for.
>
>If there any suggestio=
ns or objections, feel free to voice =

them - before 1.1 RC1 :-)
>
>Juergen
>
>
>DI J=FCrgen H=F6ller
>Se=
nior System Architect
>______________________________________
>
>werk=
3ATS - division systementwicklung
>werk3AT informations- und mediensyst=
eme
>
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>
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p://www.werk3at.com
>______________________________________
>werk3ATS =
- WIR ENTWICKELN ERFOLG
>
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