Spring can be used in standard applications, web applications, full Java EE applications, and other containers, the only requirement is that you run a standard JVM. Spring's resource abstraction allows you to load configuration files from wherever you'd like -- the classpath, the file system, FTP, and HTTP locations. You can also use Spring's resource abstraction for loading other files required for your application.

Once the IoC container is initialized, you can retrieve your Spring beans. By delegating as much bean creation as possible to Spring, there should only be a few key points where the application code needs to directly access the IoC container, and this is true even for legacy applications. ^[5] If you're developing a web application, you may not need to directly access the IoC container at all since it will automatically handle instantiation of your controller and any beans it requires.

The lowest level implementation of the IoC container is the BeanFactory, but it is recommended to use an ApplicationContext for your application. The ApplicationContext is a subclass of the BeanFactory interface so it has all the functionality a BeanFactory has and more. Unless you are writing an application that needs an extremely small memory footprint, BeanFactory shouldn't be used directly.

There are a few different ApplicationContext implementations that can be used, and we'll go over these in more detail in Chapter 5 [Currently Incomplete]. For the purposes of this example, we'll use a very popular one –ClassPathXmlApplicationContext, which defaults to reading resources from the classpath. If you need to use a different location for your classes, you can append prefixes before the configuration file's path such as 'file', 'http', etc. This will force the ApplicationContext to read from somewhere other than the default location.

                
package org.springbyexample.springindepth.chapter02.springApplication;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Message program.
 */
public class MessageRunner {

    final Logger logger = LoggerFactory.getLogger(MessageRunner.class);
    
    /**
     * Main method.
     */
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("/applicationContext.xml");

        Message message = (Message) applicationContext.getBean("message");

        logger.debug("message='" + message.getMessage() + "'");
    }

}