Creating a container with an application context

Spring provides several flavors of application context as a bean container. There are multiple core implementations of the ApplicationContext interface, as shown here:

• FileSystemXmlApplicationContext: This class is an implementation of ApplicationContext that loads application context bean definitions from the configuration files (XML) located in the file system.
• ClassPathXmlApplicationContext: This class is an implementation of ApplicationContext that loads application context bean definitions from the configuration files (XML) located in the classpath of the application.
• AnnotationConfigApplicationContext: This class is an implementation of ApplicationContext that loads application context bean definitions from the configuration classes (Java based) from the class path of the application.

Spring provides you with a web-aware implementation of the ApplicationContext interface, as shown here:

• XmlWebApplicationContext: This class is a web-aware implementation of ApplicationContext that loads application context bean definitions from the configuration files (XML) contained in a web application.
• AnnotationConfigWebApplicationContext: This class is a web-aware implementation of ApplicationContext that loads Spring web application context bean definitions from one or more Java-based configuration classes.

We can use either one of these implementations to load beans into a bean factory. It depends upon our application configuration file locations. For example, if you want to load your configuration file spring.xml from the file system in a specific location, Spring provides you with a FileSystemXmlApplicationContext, class that looks for the configuration file spring.xml in a specific location within the file system:

    ApplicationContext context = new
     FileSystemXmlApplicationContext("d:/spring.xml"); 

In the same way, you can also load your application configuration file spring.xml from the classpath of your application by using a ClassPathXmlApplicationContext class provided by Spring. It looks for the configuration file spring.xml anywhere in the classpath (including JAR files):

    ApplicationContext context = new 
     ClassPathXmlApplicationContext("spring.xml"); 

If you are using a Java configuration instead of an XML configuration, you can use AnnotationConfigApplicationContext:

    ApplicationContext context = new 
     AnnotationConfigApplicationContext(AppConfig.class); 

After loading the configuration files and getting an application context, we can fetch beans from the Spring container by calling the getBean() method of the application context:

    TransferService transferService = 
     context.getBean(TransferService.class); 

In the following section, we will learn about the Spring bean life cycle, and how a Spring container reacts to the Spring bean to create and manage it.