4. The IoC container

4. The IoC container
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4.1 Introduction

This chapter covers the Spring Framework's implementation of the Inversion of Control (IoC) ^[1] principle.

The org.springframework.beans and org.springframework.context packages provide the basis for the Spring Framework's IoC container. The BeanFactory interface provides an advanced configuration mechanism capable of managing objects of any nature. The ApplicationContext interface builds on top of the BeanFactory (it is a sub-interface) and adds other functionality such as easier integration with Spring's AOP features, message resource handling (for use in internationalization), event propagation, and application-layer specific contexts such as the WebApplicationContext for use in web applications.

In short, the BeanFactory provides the configuration framework and basic functionality, while the ApplicationContext adds more enterprise-centric functionality to it. The ApplicationContext is a complete superset of the BeanFactory, and any description of BeanFactory capabilities and behavior is to be considered to apply to the ApplicationContext as well.

BeanFactory or ApplicationContext?

Users are sometimes unsure whether a BeanFactory or an ApplicationContext is best suited for use in a particular situation. A BeanFactory pretty much just instantiates and configures beans. An ApplicationContext also does that, and it provides the supporting infrastructure to enable lots of enterprise-specific features such as transactions and AOP.

In short, favor the use of an ApplicationContext.

(For the specific details behind this recommendation, see this section.)

This chapter is divided into two parts, with the first part covering the basic principles that apply to both the BeanFactory and ApplicationContext, and with the second part covering those features that apply only to the ApplicationContext interface.

^[1]See the section entitled Background