Introduction to the Spring IoC Container and Beans

1.1. Introduction to the Spring IoC Container and Beans

This chapter covers the Spring Framework implementation of the Inversion of Control (IoC) principle. IoC is also known as dependency injection (DI). It is a process whereby objects define their dependencies (that is, the other objects they work with) only through constructor arguments, arguments to a factory method, or properties that are set on the object instance after it is constructed or returned from a factory method. The container then injects those dependencies when it creates the bean. This process is fundamentally the inverse (hence the name, Inversion of Control) of the bean itself controlling the instantiation or location of its dependencies by using direct construction of classes or a mechanism such as the Service Locator pattern.

本章介绍了控制反转(IoC)原理的Spring框架实现。IoC也被称为依赖注入(DI)。在这个过程中，对象仅通过构造函数参数、工厂方法的参数或在对象实例被构造或从工厂方法返回后在对象实例上设置的属性来定义它们的依赖项(即它们使用的其他对象)。容器在创建bean时注入这些依赖项。这个过程基本上与bean本身相反(因此得名，控制反转)，通过使用直接构造类或Service Locator模式等机制来控制其依赖关系的实例化或位置。

The org.springframework.beans and org.springframework.context packages are the basis for Spring Framework’s IoC container. The BeanFactory interface provides an advanced configuration mechanism capable of managing any type of object. ApplicationContext is a sub-interface of BeanFactory. It adds:

• Easier integration with Spring’s AOP features
• Message resource handling (for use in internationalization)
• Event publication
• Application-layer specific contexts such as the WebApplicationContext for use in web applications.

org.springframework.beans和org.springframework.context包是Spring框架IoC容器的基础。BeanFactory接口提供了一种高级的配置机制，能够管理任何类型的对象。ApplicationContext是BeanFactory的子接口。它补充道:

• 更容易与Spring的AOP特性集成
• 消息资源处理(用于国际化)
• 事件发布
• 应用程序层特定的上下文，例如用于web应用程序的WebApplicationContext。

In short, the BeanFactory provides the configuration framework and basic functionality, and the ApplicationContext adds more enterprise-specific functionality. The ApplicationContext is a complete superset of the BeanFactory and is used exclusively in this chapter in descriptions of Spring’s IoC container. For more information on using the BeanFactory instead of the ApplicationContext, see the section covering the BeanFactory API.

简而言之，BeanFactory提供了配置框架和基本功能，而ApplicationContext添加了更多特定于企业的功能。ApplicationContext是BeanFactory的一个完整超集，在本章Spring的IoC容器的描述中被专门使用。有关使用BeanFactory而不是ApplicationContext的更多信息，请参阅介绍BeanFactory API的部分。

In Spring, the objects that form the backbone of your application and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and managed by a Spring IoC container. Otherwise, a bean is simply one of many objects in your application. Beans, and the dependencies among them, are reflected in the configuration metadata used by a container.

在Spring中，构成应用程序主干并由Spring IoC容器管理的对象称为bean。bean是由Spring IoC容器实例化、组装和管理的对象。否则，bean只是应用程序中的许多对象之一。bean及其之间的依赖关系反映在容器使用的配置元数据中。