[Source code analysis] BeanFactory and FactoryBean

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BeanFacotry

The root interface for accessing a Spring bean container.
This is the basic client view of a bean container;  further interfaces such as {@link ListableBeanFactory} and {@link org.springframework.beans.factory.config.ConfigurableBeanFactory} are available for specific purposes.
This interface is implemented by objects that hold a number of bean definitions, each uniquely identified by a String name. Depending on the bean definition, the factory will return either an independent instance of a contained object (the Prototype design pattern), or a single shared instance (a superior alternative to the Singleton design pattern, in which the instance is a singleton in the scope of the factory). Which type of instance will be returned depends on the bean factory configuration: the API is the same. Since Spring 2.0, further scopes are available depending on the concrete application context (e.g. "request" and "session" scopes in a web environment).

用于访问SpringBean容器的根接口.

这是bean容器的基本客户端视图;其他接口,如{@link ListableBeanFactory}和{@link org.springframework.beans.factory.config.ConfigurableBeanFactory},可用于特定用途.

该接口由包含多个bean定义的对象实现,每个beanDefinitions are uniquely identified by a string name.根据bean定义,工厂将返回包含对象的独立实例（原型设计模式）或单个共享实例（An advanced alternative to the singleton design pattern,where instance is a singleton in factory scope）.Which type of instance is returned dependsbean工厂配置：API是相同的.自Spring 2.0以来,根据具体的应用程序上下文（例如web环境中的“请求”和“会话”范围）,More ranges can be used.

BeanFacotry是spring中比较原始的Factory.如XMLBeanFactory就是一种典型的BeanFactory.原始的BeanFactory无法支持spring的许多插件,如AOP功能、Web应用等. 
ApplicationContext接口,它由BeanFactory接口派生而来,ApplicationContext包含BeanFactory的所有功能,通常建议比BeanFactory优先

FactoryBean

 Interface to be implemented by objects used within a {@link BeanFactory} which are themselves factories for individual objects. If a bean implements this interface, it is used as a factory for an object to expose, not directly as a bean instance that will be exposed itself.

由{@link BeanFactory}The interface implemented by the object used within it,These objects are themselves factories for individual objects.如果一个bean实现了这个接口,It will be used as an object factory to expose,rather than directly as onebeaninstance to expose itself

一般情况下,Spring通过反射机制利用<bean>的class属性指定实现类实例化Bean,在某些情况下,实例化Bean过程比较复杂,如果按照传统的方式,则需要在<bean>中提供大量的配置信息.配置方式的灵活性是受限的,这时采用编码的方式可能会得到一个简单的方案.Spring为此提供了一个org.springframework.bean.factory.FactoryBean的工厂类接口,用户可以通过实现该接口定制实例化Bean的逻辑.FactoryBean接口对于Spring框架来说占用重要的地位,Spring自身就提供了70多个FactoryBean的实现.