Merging bean properties defined in two separate files

[korran]

Hi!

I'm using Spring to wire-up an application with many optional components, configured by user properties. As spring lacks any sort of conditional processing (probably for good reasons), I have decided to give each optional component its own bean definition file. When creating the application context, I can then include only those files that correspond to the enabled components.

This ends up working well for many cases, however I'm having trouble when the configuration for a particular component requires modifying the properties of one of the non-optional objects.

What I would like to do is something like this:

<!-- applicationContext-main.xml -->

<bean id="tabManager" class="foo.bar.TabManager" />
  <property name="tabs">
    <list>
      <bean class="foo.bar.CustomerTab" />
      <bean class="foo.bar.ProviderTab" />
    </list>
  </property>
</bean>

<!-- applicationContext-salesPerson.xml (optional) -->

<bean id="tabManager" parent="tabManager" />
  <property name="tabs">
    <list merge="true">
      <bean class="foo.bar.SalesPersonTab" />
    </list>
  </property>
</bean>

In case like this, there would be only one TabManager bean, named tabManager, which would have 2 or 3 tabs in it, depending on whether or not the applicationContext-salesPerson.xml file was included.

The XML above doesn't work, as Spring doesn't like beans with the same value for id and parent. I can't figure out how to override a bean, but keep some of the properties from the previous definition. Using child bean definitions as described in the documentation results in two separate beans, when all I want to do is modify the parent bean to include my extra properties.

I would prefer not to make the SalesPersonTab depend on the TabManager, but as a last resort I could have SalesPersonTab include TabManager as a constructor parameter, and add itself to the list programmatically.

Any suggestions are appreciated.

Thanks,

Kor

[korran]

By creating my own implementation of the DefaultListableBeanFactory, I was able to make the above application contexts merge together.

class MergingListableBeanFactory extends DefaultListableBeanFactory
{
  public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException
  {
    if (beanDefinition instanceof ChildBeanDefinition)
    {
      ChildBeanDefinition cbd = (ChildBeanDefinition) beanDefinition;
      if (beanName.equals(cbd.getParentName()))
      {
        AbstractBeanDefinition pbd = (AbstractBeanDefinition) super.getBeanDefinition(beanName);
        pbd.overrideFrom(cbd);
        return;
      }
    }
    super.registerBeanDefinition(beanName, beanDefinition);
  }
}