How to create parent/child contexts in a declarative way?

[pjydc]

Suppose I have a Spring web application. I have two context files:
applicationContext1.xml and applicationContext2.xml.
They are loaded into the system as follows:

web.xml:
...
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/applicationContext1.xml
/WEB-INF/applicationContext2.xml
</param-value>
</context-param>
...

Based on the two files, I want to create two contexts
with a child/parent relationship. Can I?
How can I make one context is the child of the other one
in a declarative way?

Thanks,
Pete

[Colin Sampaleanu]

This is quite easy using the built in optional loading of a parent context to the main web app context, that the ContextLoader can do.

web.xml:
...
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>
      /WEB-INF/applicationContext1.xml
    </param-value>
  </context-param>

  <!--  load a shared service layer parent application context -->
  <context-param>
    <param-name>locatorFactorySelector</param-name>
    <param-value>beanRefContext.xml</param-value>
  </context-param>
  <context-param>
    <param-name>parentContextKey</param-name>
    <param-value>servicelayer-context</param-value>
  </context-param>

and in beanRefContext.xml, somewhere on your classpath:

<?xml version="1.0" encoding="UTF-8"?>
<!-- $Id&#58; beanRefContext.xml,v 1.1 2004/11/14 17&#58;19&#58;19 colins Exp $ -->
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http&#58;//www.springframework.org/dtd/spring-beans.dtd">

<!-- load a hierarchy of contexts, although there is just one here -->

<beans>

  <bean id="servicelayer-context"
  	    class="org.springframework.context.support.ClassPathXmlApplicationContext">
    <constructor-arg>
      <list>
        <value>/WEB-INF/applicationContext2.xml</value>
      </list>
   	</constructor-arg>
  </bean>

</beans>

The loading of the shared parent context happens via ContextSingletonBeanFactoryLocator. Take a look at the JavaDocs for that to get an idea of what is going on.

Note this is a _shared_ parent context. Any other webapps in the same EAR file (if uisng an EAR file) that specify the same beanRefContext will share the same parent context, and the same woiuld happen with any other utility code that did the same thing...

Regards,

[saden1]

Why isn't this topic covered in the Spring documentation?

Thanks Colin for the post.

Tag: ContextLoader, Sharing Beans Between Web Applications, Loading Beans Once.