java - Is there a way to re-use a <util:list> in spring configuration file?

Question

I have a bunch of rules to be injected into a set of classes, something like below:

<bean id="rule1" class="com.vikdor.rules.Rule1" />
<bean id="rule2" class="com.vikdor.rules.Rule2" />
<bean id="rule3" class="com.vikdor.rules.Rule3" />
<bean id="rule4" class="com.vikdor.rules.Rule4" />
<bean id="rule5" class="com.vikdor.rules.Rule5" />

<util:list id="commonRules">
    <ref bean="rule1" />
    <ref bean="rule3" />
    <ref bean="rule5" />
</util:list>

<util:list id="normalInvRules">
   <!-- Include common rules -->
   <ref bean="rule4" />
</util:list>

<util:list id="prepaidInvRules">
   <!-- Include common rules -->
   <ref bean="rule2" />
</util:list>

How can I include the common rules list in the lists corresponding to normalInvRules and prepaidInvRules?

The number of rules (e.g. rule1, rule2 etc.,) are more and the number groups (normalInvRules, prepaidInvRules etc.,) are also more. So, I am wondering if there is a way to avoid repeating the common rules and just list only the specific ones and include the reference to the common list.

Answer 1

There is a feature called 'collection merging' that does exactly this. See section 3.3.3.4.1. "Collection merging" in the Spring documentation or the 2008 blog post (with an example) that I wrote on the subject.