Configuring bean lists from properties?

[hgschmie]

Hi,

I have a bean definition basically like this:

<bean id="factory">
  <property name="listeners">
    <map>
      <entry type="type1">
        <list>
          <bean class="listener.type.one" />
          <bean class="listener.type.two" />
        </list>
      </entry>
    </map>
  </property>
</bean>

I use this bean definition as part of a module that gets plugged into
a number of larger applications. In one of these apps, I have to redo
this definition because I have a third listener.

What I want do is, to define the listeners in a properties file, e.g.

factory.listeners.type1 = listener.type.one, listener.type.two

and for my special case:

factory.listeners.type1 = listener.type.one, listener.type.two, listener.type.three

and use some sort of placeholder replacement for the

<list>
  <bean class="listener.type.one" />
  <bean class="listener.type.two" />
</list>

block of the bean definition. Or just the list itself. I scratched my
head over BeanFactoryPostProcessor definitions but I simply can not
see a way to intercept the List creation at bean creation time or the
variable number of elements at declaration time. I'm very grateful for
hints.

Thanks
Henning

[karldmoore]

Have you looked at Collection merging at all?
http://www.springframework.org/docs/...ction-elements

[hgschmie]

Yes, of course. If I use collection merging, then I would need a child bean definition in every application, something that I try to avoid because then the module (which also uses the factory) would need a dependency on the child bean. Something like this:

Current state:

module:

<beans>
  <bean id="factory">
   ...
  </bean>
  <bean id="factoryUser">
    <property name="factory" ref="factory"/>
    ...
  </bean>
</beans>

application:

<beans>
  <bean id="appFactoryUser">
    <property name="factory" ref="factory"/>
    ...
  </bean>
</beans>

When using Collection merging:

module:

<beans>
  <bean id="abstractFactory" abstract="true">
   ...
  </bean>
  <bean id="factoryUser">
    <property name="factory" ref="factory"/> [1]
    ...
  </bean>
</beans>

application:

<beans>
  <bean id="factory" parent="abstractFactory">
   [... do our happy collection merging ...]
  </bean>

  <bean id="appFactoryUser">
    <property name="factory" ref="factory"/>
    ...
  </bean>
</beans>

Now you have a back-reference between module and application at [1]: The module expects the application to define a bean called "factory". Bad. I also have an abstract Bean that I did not need before. Makes the module harder to test.

Yes, I did read the manual. I even understood most of it. :-)

[karldmoore]

I'm sure I've seen examples in the past using PropertyPlaceholderConfigurer and relying on StringArrayPropertyEditor convert the injected value.
http://www.springframework.org/docs/...rtyEditor.html

[hgschmie]

I have a list of bean objects, not a list of bean names. And I need this as
value part of a map, which takes object, so a PropertyEditor will probably not
work here.