Especially when defining transactional proxies, you may end up with many similar proxy definitions. The use of parent and child bean definitions, along with inner bean definitions, can result in much cleaner and more concise proxy definitions.
First a parent, template, bean definition is created for the proxy:
<bean id="txProxyTemplate" abstract="true" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"> <property name="transactionManager" ref="transactionManager"/> <property name="transactionAttributes"> <props> <prop key="*">PROPAGATION_REQUIRED</prop> </props> </property> </bean>
This will never be instantiated itself, so may actually be incomplete. Then each proxy which needs to be created is just a child bean definition, which wraps the target of the proxy as an inner bean definition, since the target will never be used on its own anyway.
<bean id="myService" parent="txProxyTemplate"> <property name="target"> <bean class="org.springframework.samples.MyServiceImpl"> </bean> </property> </bean>
It is of course possible to override properties from the parent template, such as in this case, the transaction propagation settings:
<bean id="mySpecialService" parent="txProxyTemplate"> <property name="target"> <bean class="org.springframework.samples.MySpecialServiceImpl"> </bean> </property> <property name="transactionAttributes"> <props> <prop key="get*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="find*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="load*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="store*">PROPAGATION_REQUIRED</prop> </props> </property> </bean>
Note that in the example above, we have explicitly marked the parent bean definition as abstract by using the abstract attribute, as described previously, so that it may not actually ever be instantiated. Application contexts (but not simple bean factories) will by default pre-instantiate all singletons. It is therefore important (at least for singleton beans) that if you have a (parent) bean definition which you intend to use only as a template, and this definition specifies a class, you must make sure to set the abstract attribute to true, otherwise the application context will actually try to pre-instantiate it.