spring beans源码解读之--BeanFactory的注册

beanFactory的继承关系如下图所示：

(图片来源：http://www.myexception.cn/software-architecture-design/925888.html)

在上节beanFactory的进化史，我们就讲到了上图的左边部分，这次我们来分析一下图的右边部分。AliasRegistry 是一个用于别名管理的通用接口，BeanDefinitionRegistry继承了该接口。

SimpleAliasRegistry作为一个基类，实现了AliasRegistry接口。

SingletonBeanRegistry是spring 提供的一个共享bean的注册接口。实现该接口可以方便对单例进行管理。

public interface SingletonBeanRegistry {

    /**
     * Register the given existing object as singleton in the bean registry,
     * under the given bean name.
     * <p>The given instance is supposed to be fully initialized; the registry
     * will not perform any initialization callbacks (in particular, it won't
     * call InitializingBean's {@code afterPropertiesSet} method).
     * The given instance will not receive any destruction callbacks
     * (like DisposableBean's {@code destroy} method) either.
     * <p>When running within a full BeanFactory: <b>Register a bean definition
     * instead of an existing instance if your bean is supposed to receive
     * initialization and/or destruction callbacks.</b>
     * <p>Typically invoked during registry configuration, but can also be used
     * for runtime registration of singletons. As a consequence, a registry
     * implementation should synchronize singleton access; it will have to do
     * this anyway if it supports a BeanFactory's lazy initialization of singletons.
     * @param beanName the name of the bean
     * @param singletonObject the existing singleton object
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     * @see org.springframework.beans.factory.DisposableBean#destroy
     * @see org.springframework.beans.factory.support.BeanDefinitionRegistry#registerBeanDefinition
     */
    void registerSingleton(String beanName, Object singletonObject);

    /**
     * Return the (raw) singleton object registered under the given name.
     * <p>Only checks already instantiated singletons; does not return an Object
     * for singleton bean definitions which have not been instantiated yet.
     * <p>The main purpose of this method is to access manually registered singletons
     * (see {@link #registerSingleton}). Can also be used to access a singleton
     * defined by a bean definition that already been created, in a raw fashion.
     * <p><b>NOTE:</b> This lookup method is not aware of FactoryBean prefixes or aliases.
     * You need to resolve the canonical bean name first before obtaining the singleton instance.
     * @param beanName the name of the bean to look for
     * @return the registered singleton object, or {@code null} if none found
     * @see ConfigurableListableBeanFactory#getBeanDefinition
     */
    Object getSingleton(String beanName);

    /**
     * Check if this registry contains a singleton instance with the given name.
     * <p>Only checks already instantiated singletons; does not return {@code true}
     * for singleton bean definitions which have not been instantiated yet.
     * <p>The main purpose of this method is to check manually registered singletons
     * (see {@link #registerSingleton}). Can also be used to check whether a
     * singleton defined by a bean definition has already been created.
     * <p>To check whether a bean factory contains a bean definition with a given name,
     * use ListableBeanFactory's {@code containsBeanDefinition}. Calling both
     * {@code containsBeanDefinition} and {@code containsSingleton} answers
     * whether a specific bean factory contains a local bean instance with the given name.
     * <p>Use BeanFactory's {@code containsBean} for general checks whether the
     * factory knows about a bean with a given name (whether manually registered singleton
     * instance or created by bean definition), also checking ancestor factories.
     * <p><b>NOTE:</b> This lookup method is not aware of FactoryBean prefixes or aliases.
     * You need to resolve the canonical bean name first before checking the singleton status.
     * @param beanName the name of the bean to look for
     * @return if this bean factory contains a singleton instance with the given name
     * @see #registerSingleton
     * @see org.springframework.beans.factory.ListableBeanFactory#containsBeanDefinition
     * @see org.springframework.beans.factory.BeanFactory#containsBean
     */
    boolean containsSingleton(String beanName);

    /**
     * Return the names of singleton beans registered in this registry.
     * <p>Only checks already instantiated singletons; does not return names
     * for singleton bean definitions which have not been instantiated yet.
     * <p>The main purpose of this method is to check manually registered singletons
     * (see {@link #registerSingleton}). Can also be used to check which singletons
     * defined by a bean definition have already been created.
     * @return the list of names as a String array (never {@code null})
     * @see #registerSingleton
     * @see org.springframework.beans.factory.support.BeanDefinitionRegistry#getBeanDefinitionNames
     * @see org.springframework.beans.factory.ListableBeanFactory#getBeanDefinitionNames
     */
    String[] getSingletonNames();

    /**
     * Return the number of singleton beans registered in this registry.
     * <p>Only checks already instantiated singletons; does not count
     * singleton bean definitions which have not been instantiated yet.
     * <p>The main purpose of this method is to check manually registered singletons
     * (see {@link #registerSingleton}). Can also be used to count the number of
     * singletons defined by a bean definition that have already been created.
     * @return the number of singleton beans
     * @see #registerSingleton
     * @see org.springframework.beans.factory.support.BeanDefinitionRegistry#getBeanDefinitionCount
     * @see org.springframework.beans.factory.ListableBeanFactory#getBeanDefinitionCount
     */
    int getSingletonCount();

}

注册接口的默认实现为：DefaultSingletonBeanRegistry，主要作用是提供能被所有调用者共享bean的注册，调用者可用通过bean 名称获取到该bean的实例。同时该类也提供了对注册bean的销毁方法。

DefaultSingletonBeanRegistry也实现了AliasRegistry接口，增加了对别名的管理。

FactoryBeanRegistrySupport 集成了DefaultSingletonBeanRegistry对bean的单例bean的管理功能，是一个基类，用来处理FactoryBean实例的单例bean的注册。

我们重点介绍来研究一下AbstractBeanFactory的代码：

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
// to do more
}

从继承关系上来讲，AbstractBeanFactory具备了ConfigurableBeanFactory 的完整功能，