how Spring finds applicationContext xml

Spring can be easily integrated into any Java-based web framework. All you need to do is to declare the ContextLoaderListener in your web.xml and use a contextConfigLocation <context-param> to set which context files to load.

The <context-param>:


The <listener>:


NOTE: Listeners were added to the Servlet API in version 2.3. If you have a Servlet 2.2 container, you can use the ContextLoaderServlet to achieve this same functionality.

If you don’t specify the contextConfigLocation context parameter, the ContextLoaderListener will look for a /WEB-INF/applicationContext.xml file to load. Once the context files are loaded, Spring creates aWebApplicationContext object based on the bean definitions and puts it into the ServletContext.

All Java web frameworks are built on top of the Servlet API, so you can use the following code to get the ApplicationContext that Spring created.

WebApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);

The WebApplicationContextUtils class is for convenience, so you don’t have to remember the name of the ServletContext attribute. Its getWebApplicationContext() method will return null if an object doesn’t exist under theWebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE key. Rather than risk getting NullPointerExceptions in your application, it’s better to use the getRequiredWebApplicationContext() method. This method throws an Exception when the ApplicationContext is missing.

Once you have a reference to the WebApplicationContext, you can retrieve beans by their name or type. Most developers retrieve beans by name, then cast them to one of their implemented interfaces.




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