spring: application context vs bean factory

      bean factory to read the bean definitions from the Resource. But the bean factory doesn’t instantiate the beans just yet. Beans are “lazily” loaded into bean factories, meaning that while the bean factory will immediately load the bean definitions (the description of beans and their properties),

the beans themselves will not be instantiated until they are needed.

     When getBean() is called, the factory will instantiate the bean and set the bean’s properties using DI. Thus begins the life of a bean within the Spring container.

     A bean factory is fine for simple applications, but to take advantage of the full power of the Spring Framework, you’ll probably want to load your application beans using Spring’s more advanced container: the application context.

    On the surface, an ApplicationContext is much the same as a BeanFactory. Both load bean definitions, wire beans together, and dispense beans upon request. But an ApplicationContext offers much more:

 

      ■ Application contexts provide a means for resolving text messages, including support for internationalization (I18N) of those messages.

      ■ Application contexts provide a generic way to load file resources, such as images.

      ■ Application contexts can publish events to beans that are registered as listeners.

Because of the additional functionality it provides, an ApplicationContext is preferred over a BeanFactory in nearly all applications. The only times you might consider using a BeanFactory are in circumstances where resources are scarce, such as a mobile device. We will be using an ApplicationContext

    

     Aside from the additional functionality offered by application contexts,another big difference between an application context and a bean factory is how singleton beans are loaded. A bean factory lazily loads all beans, deferring bean creation until the getBean() method is called. An application context is a bit smarter and preloads all singleton beans upon context startup. By preloading singleton beans, you ensure that they will be ready to use when needed—your application won’t have to wait for them to be created.