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Declarative Usage of Application Contexts

Following IoC principles, as little application code as possible should know about the application context. However, it is sometimes necessary for a smal amount of glue code to know about the context. For a Spring-enabled J2EE web-app, it is possible to reduce or completely eliminate even this small amount of code by using Spring code to declaratively specify that an application context should be loaded at web-app startup.

Spring's ContextLoader is the class that provides this capability. However, it must actually be instigated by using another helper class like

...
<listener>
  <listener-class>org.springframework.web.context.ContextLoaderListener</listener-
class>
</listener>
...
When the web-app starts up, the listener or servlet will execute ContextLoader, which initializes and starts an XmlWebApplicationContext based on one or more XML file fragments that are merged. By default, it will use:
/WEB-INF/applicationContext.xml
but you may this to point to one or more files in an alternate location by using the contextConfiglocation servlet context param in the web.xml file as in the following two examples:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>WEB-INF/myApplicationContext.xml</param-value>
</context-param>


<context-param>
  <param-name>contextConfigLocation</param-name>
  <param-value>classpath:services-applicationContext.xml,
               classpath:dao-applicationContext.xml
  </param-value>
</context-param>

Any Application code that needs to access the application contexgt may do so by calling a static helper method from the WebApplicationContextUtils class:
WebApplicationContext getWebapplicationcontext(ServletContext sc)


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