Spring BeanFactory源码学习

一.BeanFactory

　　BeanFactory是Spring IOC容器的基础，是IOC容器的基础接口，所有的容器都是从它这里继承实现而来。BeanFactory提供了最基本的IOC容器的功能，即所有的容器至少需要实现的标准。BeanFactory体系结构是典型的工厂方法模式，即什么样的工厂生产什么样的产品。BeanFactory是最基本的抽象工厂，而其他的IOC容器只不过是具体的工厂，对应着各自的Bean定义方法。但同时，其他容器也针对具体场景不同，进行了扩充，提供具体的服务。

二.BeanFacory源码

1.java doc

　　首先是Java doc,现在阅读源码的习惯是一定要理解了java doc的描述，因为这里是作者的描述，没有人比作者更明白这个类，这个接口要干什么。

/**
 * 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.
 *
 * <p>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).
 *
 * <p>The point of this approach is that the BeanFactory is a central registry
 * of application components, and centralizes configuration of application
 * components (no more do individual objects need to read properties files,
 * for example). See chapters 4 and 11 of "Expert One-on-One J2EE Design and
 * Development" for a discussion of the benefits of this approach.
 *
 * <p>Note that it is generally better to rely on Dependency Injection
 * ("push" configuration) to configure application objects through setters
 * or constructors, rather than use any form of "pull" configuration like a
 * BeanFactory lookup. Spring's Dependency Injection functionality is
 * implemented using this BeanFactory interface and its subinterfaces.
 *
 * <p>Normally a BeanFactory will load bean definitions stored in a configuration
 * source (such as an XML document), and use the {@code org.springframework.beans}
 * package to configure the beans. However, an implementation could simply return
 * Java objects it creates as necessary directly in Java code. There are no
 * constraints on how the definitions could be stored: LDAP, RDBMS, XML,
 * properties file, etc. Implementations are encouraged to support references
 * amongst beans (Dependency Injection).
 *
 * <p>In contrast to the methods in {@link ListableBeanFactory}, all of the
 * operations in this interface will also check parent factories if this is a
 * {@link HierarchicalBeanFactory}. If a bean is not found in this factory instance,
 * the immediate parent factory will be asked. Beans in this factory instance
 * are supposed to override beans of the same name in any parent factory.
 *
 * <p>Bean factory implementations should support the standard bean lifecycle interfaces
 * as far as possible. The full set of initialization methods and their standard order is:<br>
 * 1. BeanNameAware's {@code setBeanName}<br>
 * 2. BeanClassLoaderAware's {@code setBeanClassLoader}<br>
 * 3. BeanFactoryAware's {@code setBeanFactory}<br>
 * 4. ResourceLoaderAware's {@code setResourceLoader}
 * (only applicable when running in an application context)<br>
 * 5. ApplicationEventPublisherAware's {@code setApplicationEventPublisher}
 * (only applicable when running in an application context)<br>
 * 6. MessageSourceAware's {@code setMessageSource}
 * (only applicable when running in an application context)<br>
 * 7. ApplicationContextAware's {@code setApplicationContext}
 * (only applicable when running in an application context)<br>
 * 8. ServletContextAware's {@code setServletContext}
 * (only applicable when running in a web application context)<br>
 * 9. {@code postProcessBeforeInitialization} methods of BeanPostProcessors<br>
 * 10. InitializingBean's {@code afterPropertiesSet}<br>
 * 11. a custom init-method definition<br>
 * 12. {@code postProcessAfterInitialization} methods of BeanPostProcessors
 *
 * <p>On shutdown of a bean factory, the following lifecycle methods apply:<br>
 * 1. DisposableBean's {@code destroy}<br>
 * 2. a custom destroy-method definition

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