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POspring - constructor injection and overriding parent definition of nested bean
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  1. POspring - constructor injection and overriding parent definition of nested bean
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    copied!<p>I've read the Spring 3 reference on <a href="http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-child-bean-definitions" rel="nofollow noreferrer">inheriting bean definitions</a>, but I'm confused about what is possible and not possible.</p> <p>For example, a bean that takes a collaborator bean, configured with the value 12</p> <pre><code>&lt;bean name="beanService12" class="SomeSevice"&gt; &lt;constructor-arg index="0" ref="serviceCollaborator1"/&gt; &lt;/bean&gt; &lt;bean name="serviceCollaborator1" class="SomeCollaborator"&gt; &lt;constructor-arg index="0" value="12"/&gt; &lt;!-- more cargs, more beans, more flavor --&gt; &lt;/bean&gt; </code></pre> <p>I'd then like to be able to create similar beans, with slightly different configured collaborators. Can I do something like</p> <pre><code> &lt;bean name="beanService13" parent="beanService12"&gt; &lt;constructor-arg index="0"&gt; &lt;bean&gt; &lt;constructor-arg index="0" value="13"/&gt; &lt;/bean&gt; &lt;/constructor&gt; &lt;/bean&gt; </code></pre> <p>I'm not sure this is possible and, if it were, it feels a bit clunky. Is there a nicer way to override small parts of a large nested bean definition? It seems the child bean has to know quite a lot about the parent, e.g. constructor index.</p> <p>This is a toy example - in practice the service is a large bean definition relying on many other collaborator beans, which have also other bean dependencies. For example, a chain of handlers were created with each bean referencing the next in the chain, which references the next. I want to create an almost identical chain with some small changes to handlers in the middle, how do I it?</p> <p>I'd prefer not to change the structure - the service beans use collaborators to perform their function, but I can add properties and use property injection if that helps. </p> <p>This is a repeated pattern, would creating a custom schema help?</p> <p>Thanks for any advice!</p> <p>EDIT: The nub of my question is, if I have a really large bean definition, with a complex hiearchy of beans being created (bean having properites that are bean etc.), and I want to create a bean that is almost the same with a few changes, how to I do it? Please mention if your solution has to use properites, or if constructor injection can be used.</p> <p>Nested vs. top-level beans are not the issue (in fact, I think all the beans are top level in practice.)</p> <p>EDIT2: Thank you for your answers so far. A FactoryBean might be the answer, since that will reduce the complexity of the spring context, and allow me to specify just the differences as parameters to the factory. But, pushing a chunk of context back into code doesn't feel right. I've heard that spring can be used with scripts, e.g. groovy - does that provide an alternative? Could the factory be created in groovy?</p>
 

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