What is the difference between spring parent context and child context?

Question

I was reading spring doc the core container I want to understand the purpose of ref parent when inject collaborators then I found this notion of parent context child context or parent container and current container this is the part that I'm confuse about it : This part of doc

Specifying the target bean through the parent attribute creates a reference to a bean that is in a parent container of the current container. The value of the parent attribute may be the same as either the id attribute of the target bean, or one of the values in the name attribute of the target bean, and the target bean must be in a parent container of the current one. You use this bean reference variant mainly when you have a hierarchy of containers and you want to wrap an existing bean in a parent container with a proxy that will have the same name as the parent bean.

<!-- in the parent context -->
<bean id="accountService" class="com.foo.SimpleAccountService">
    <!-- insert dependencies as required as here -->
</bean>
<!-- in the child (descendant) context -->
<bean id="accountService" <!-- bean name is the same as the parent bean -->
    class="org.springframework.aop.framework.ProxyFactoryBean">
    <property name="target">
        <ref parent="accountService"/> <!-- notice how we refer to the parent bean -->
    </property>
    <!-- insert other configuration and dependencies as required here -->
</bean>

can someone give me some help or an example of this two type of context ? and what is the purpose of the ref parent Thank you in advance

Answer 1

The beans of the Spring run inside an application context.

The Application Context is Spring's advanced container. Similar to BeanFactory, it can load bean definitions, wire beans together, and dispense beans upon request. Additionally, it adds more enterprise-specific functionality such as the ability to resolve textual messages from a properties file and the ability to publish application events to interested event listeners. This container is defined by org.springframework.context.ApplicationContext interface. https://www.tutorialspoint.com/spring/spring_applicationcontext_container.htm

For each application context you can have many configuration files, configuration classes or a mix of both.

You can create an application context with a code like this:

ApplicationContext context = new FileSystemXmlApplicationContext("Beans.xml");

And obtain the beans with context.getBean or with @autowired.

There are some cases when you want(or need) to have a context hierarchy. In these cases Spring provides a way of specifying a parent context. If you look at this constructor, you will see that it receives a context parent.

http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/support/FileSystemXmlApplicationContext.html#FileSystemXmlApplicationContext-org.springframework.context.ApplicationContext-

As you can see the parent context is the same type of a child context, they both are http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/ApplicationContext.html.

The difference is that they are related through a parent/child relationship. Not a compose(import) relationship.

The most common case where you see this is in a Spring MVC application, this applications have 2 context, the first is the dispatcher servlet context and the other one is the root context. Here you can see the relationship http://docs.spring.io/spring/docs/3.0.x/spring-framework-reference/html/mvc.html#mvc-servlet

And here you can see an example of application context hierarchy in spring boot applications.

https://dzone.com/articles/spring-boot-and-application-context-hierarchy