1、FactoryBean
You can implement the org.springframework.beans.factory.FactoryBean interface for objects that are themselves factories.
The FactoryBean interface is a point of pluggability into the Spring IoC container’s instantiation logic. If you have complex initialization code that is better expressed in Java as opposed to a (potentially) verbose amount of XML, you can create your own FactoryBean, write the complex initialization inside that class, and then plug your custom FactoryBean into the container.
The FactoryBean interface provides three methods:
Object getObject(): Returns an instance of the object this factory creates. The instance can possibly be shared, depending on whether this factory returns singletons or prototypes.
boolean isSingleton(): Returns true if this FactoryBean returns singletons or false otherwise.
Class getObjectType(): Returns the object type returned by the getObject() method or null if the type is not known in advance.
The FactoryBean concept and interface is used in a number of places within the Spring Framework. More than 50 implementations of the FactoryBean interface ship with Spring itself.
When you need to ask a container for an actual FactoryBean instance itself instead of the bean it produces, preface the bean’s id with the ampersand symbol (&) when calling the getBean() method of the ApplicationContext. So, for a given FactoryBean with an id of myBean, invoking getBean(“myBean”) on the container returns the product of the FactoryBean, whereas invoking getBean("&myBean") returns the FactoryBean instance itself.
一般情况下，Spring通过反射机制利用的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50多个FactoryBean的实现。它们隐藏了实例化一些复杂Bean的细节，给上层应用带来了便利。从Spring3.0开始，FactoryBean开始支持泛型，即接口声明改为FactoryBean的形式。
以Bean结尾，表示它是一个Bean，不同于普通Bean的是：它是实现了FactoryBean接口的Bean，根据该Bean的ID从BeanFactory中获取的实际上是FactoryBean的getObject()返回的对象，而不是FactoryBean本身，如果要获取FactoryBean对象，请在id前面加一个&符号来获取。
简言之：当你的某个业务Bean实例化的逻辑比较复杂的时候，就可以考虑实现FactoryBean接口，通过getObject方法构造自己需要复杂Bean对象，在Spring框架本身包含50多个实现类，除此之外非常流行的框架Mybatis和Hibernate也是用了这个特性（他们都通过SqlSessionFactoryBean构造SqlSessionFactory实例）。FactoryBean本身也是spring容器管理的Bean，只不过这个Bean不是简单的Bean，而是一个能生产或者修饰对象生成的工厂Bean,它的实现与设计模式中的工厂模式和修饰器模式类似 。根据该Bean的ID从BeanFactory中获取getBean(“myBean”)的实际上是FactoryBean的getObject()返回的对象，而不是FactoryBean本身，如果要获取FactoryBean对象，需要在id前面加一个&符号来获取getBean("&myBean")。
2、BeanFactory
The BeanFactory API provides the underlying basis for Spring’s IoC functionality. Its specific contracts are mostly used in integration with other parts of Spring and related third-party frameworks, and its DefaultListableBeanFactory implementation is a key delegate within the higher-level GenericApplicationContext container.
BeanFactory，以Factory结尾，表示它是一个工厂类(接口)， 它负责生产和管理bean的一个工厂。在Spring中，BeanFactory是IOC容器的核心接口，它的职责包括：实例化、定位、配置应用程序中的对象及建立这些对象间的依赖。BeanFactory只是个接口，并不是IOC容器的具体实现，但是Spring容器给出了很多种实现，如DefaultListableBeanFactory、XmlBeanFactory、ApplicationContext等，其中XmlBeanFactory就是常用的一个，该实现将以XML方式描述组成应用的对象及对象间的依赖关系。XmlBeanFactory类将持有此XML配置元数据，并用它来构建一个完全可配置的系统或应用。
BeanFactory：是Spring里面Bean工厂的接口，只提供了实例化对象和拿对象的简单功能并不支持spring的很多插件如AOP功能；只有获取对象的时候才会实例化。
3、ApplicationContext
The org.springframework.context package adds the ApplicationContext interface, which extends the BeanFactory interface, in addition to extending other interfaces to provide additional functionality in a more application framework-oriented style. Many people use the ApplicationContext in a completely declarative fashion, not even creating it programmatically, but instead relying on support classes such as ContextLoader to automatically instantiate an ApplicationContext as part of the normal startup process of a Java EE web application.
To enhance BeanFactory functionality in a more framework-oriented style, the context package also provides the following functionality:
1）Access to messages in i18n-style, through the MessageSource interface.
2）Access to resources, such as URLs and files, through the ResourceLoader interface.
3）Event publication, namely to beans that implement the ApplicationListener interface, through the use of the ApplicationEventPublisher interface.
4）Loading of multiple (hierarchical) contexts, letting each be focused on one particular layer, such as the web layer of an application, through the HierarchicalBeanFactory interface.
ApplicationContext是BeanFactory 的子接口，包含BeanFactory的所有功能，通常都优先使用ApplicationContext。
ApplicationContext以一种更向面向框架的方式工作以及对上下文进行分层和实现继承，ApplicationContext新增了以下的功能：
1）MessageSource, 提供国际化的消息访问；
2）资源访问，如URL和文件 ；
3） 事件传播 ；
4:）载入多个（有继承关系）上下文 ，使得每一个上下文都专注于一个特定的层次，比如应用的web层。
| Feature | BeanFactory | ApplicationContext |
|---|---|---|
| Bean instantiation/wiring | Yes | Yes |
| Integrated lifecycle management | No | Yes |
| Automatic BeanPostProcessor registration | No | Yes |
| Automatic BeanFactoryPostProcessor registration | No | Yes |
| Convenient MessageSource access (for internalization) | No | Yes |
| Built-in ApplicationEvent publication mechanism | No | Yes |
总结：ApplicationContext继承BeanFactory接口，提供了更多的的功能；国际化、消息机制、AOP等，容器启动就会实例化对象，当然可以配置延迟加载。
