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javaspringjmshornetq

How does Spring start this app?

I'm parsing through some inherited code of a Java app that is deployed as a WAR file in JBOSS, and uses Spring, JMS, and HornetQ. I'm trying to figure out, for lack of a better phrase, what makes the app "go". Most of the Spring examples I've seen include an application with a main() method, which imperatively acts on the beans provided by the Spring context in some way. This application has no main(). As far as I can tell, this is what's happening:

The WAR file's web.xml uses a listener to launch Spring when the application starts in JBOSS, and passes it a config file

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:application-context.xml</param-value>
</context-param>

Spring then processes the application-context.xml file, which includes this snippet:

<bean id="jmsContainer"
    class="org.springframework.jms.listener.DefaultMessageListenerContainer">
    <property name="connectionFactory" ref="connectionFactory" />
    <property name="destination" ref="destination" />
    <property name="messageListener" ref="appListenerProxy" />

Through a couple more references in the application-context.xml, the "appListenerProxy" ultimately refers to a class in the application that implements SessionAwareMessageListener, which responds to messages on a queue.

The part that's tripping me up is that I don't see any kind of code to get the jmsContainer bean and do something with it. Is that a well-defined ID, such that the Spring framework is looking for it? And if so, is that documented somewhere (along with other IDs the framework might be looking for)? http://docs.spring.io/spring/docs/current/spring-framework-reference/html/jms.html seemed to be the closest I found, but it doesn't really specify whether that ID is just in the examples by convention, or if it's a meaningful string.

Thanks

Solution

  • Containers in spring are part of the framework core. The Framework will scan all the containers that implement a certain container interface, and initialize them.

    This also relies on the Inversion of Control (IoC) principle.

    For more information on IoC Container, check this page: IoC Container