Bean Definition Inheritance

Why do we need it?

• Used for common set of definitions across multiple beans
• Inherit bean definition across other beans
• Can be a bean itself
• Can be an abstract bean, just to be overridden

Example

config.xml

<bean id="parentbean" class="...">
<property name="commonPropertyName" value="commonValue" />
</bean>

<bean id="childA" class="..." parent="parentbean">
<property name="childAPropertyName" value="childAValue" />
</bean>

<bean id="childB" class="..." parent="parentbean">
<property name="childBPropertyName" value="childBValue" />
</bean>

childA and childB will both inherit the property definition commonPropertyName with a value of commonValue, but will each have their own properties as well.

Example with Lists

config.xml

<bean id="parentbean" class="...">
<property name="mylist">
<list>
<value ref="dependentBean1" />
<value ref="dependentBean2" />
</list>
</property>
</bean>

<bean id="childA" class="..." parent="parentbean">
<property name="mylist">
<list>
<value ref="dependentBean3" />
</list>
</property>
</bean>

<bean id="childB" class="..." parent="parentbean">
<property name="mylist">
<list merge="true">
<value ref="dependentBean4" />
</list>
</property>
</bean>

childA and childB will both inherit the mylist property containing dependentBean1 and dependentBean2.

However

• childA will override the property values inherited with its single value of dependentBean3
• childB will merge the inherited property values with dependentBean4

Making the Parent Bean Abstract

config.xml

<bean id="parentbean" class="..." abstract="true">
<property name="mylist">
<list>
<value ref="dependentBean1" />
<value ref="dependentBean2" />
</list>
</property>
</bean>

...