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《深入理解Spring系列之一：开篇》中提到在Spring容器启动的过程中，会将类解析成Spring内部的BeanDefinition结构，并将BeanDefinition存储到一个叫DefaultListableBeanFactory中，本篇将深入分析BeanFactory

首先，看一下DefaultListableBeanFactory的类图，

可以看到 DefaultListableBeanFactory 间接实现了BeanFactory接口，先来分析一下这个BeanFactory，直接查看BeanFactory源代码，

public interface BeanFactory {/*** Used to dereference a {@link FactoryBean} instance and distinguish it from* beans <i>created</i> by the FactoryBean. For example, if the bean named* {@code myJndiObject} is a FactoryBean, getting {@code &myJndiObject}* will return the factory, not the instance returned by the factory.*/String FACTORY_BEAN_PREFIX = "&";/*** Return an instance, which may be shared or independent, of the specified bean.* <p>This method allows a Spring BeanFactory to be used as a replacement for the* Singleton or Prototype design pattern. Callers may retain references to* returned objects in the case of Singleton beans.* <p>Translates aliases back to the corresponding canonical bean name.* Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the name of the bean to retrieve* @return an instance of the bean* @throws NoSuchBeanDefinitionException if there is no bean definition* with the specified name* @throws BeansException if the bean could not be obtained*/Object getBean(String name) throws BeansException;/*** Return an instance, which may be shared or independent, of the specified bean.* <p>Behaves the same as {@link #getBean(String)}, but provides a measure of type* safety by throwing a BeanNotOfRequiredTypeException if the bean is not of the* required type. This means that ClassCastException can't be thrown on casting* the result correctly, as can happen with {@link #getBean(String)}.* <p>Translates aliases back to the corresponding canonical bean name.* Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the name of the bean to retrieve* @param requiredType type the bean must match. Can be an interface or superclass* of the actual class, or {@code null} for any match. For example, if the value* is {@code Object.class}, this method will succeed whatever the class of the* returned instance.* @return an instance of the bean* @throws NoSuchBeanDefinitionException if there is no such bean definition* @throws BeanNotOfRequiredTypeException if the bean is not of the required type* @throws BeansException if the bean could not be created*/<T> T getBean(String name, Class<T> requiredType) throws BeansException;/*** Return an instance, which may be shared or independent, of the specified bean.* <p>Allows for specifying explicit constructor arguments / factory method arguments,* overriding the specified default arguments (if any) in the bean definition.* @param name the name of the bean to retrieve* @param args arguments to use when creating a bean instance using explicit arguments* (only applied when creating a new instance as opposed to retrieving an existing one)* @return an instance of the bean* @throws NoSuchBeanDefinitionException if there is no such bean definition* @throws BeanDefinitionStoreException if arguments have been given but* the affected bean isn't a prototype* @throws BeansException if the bean could not be created* @since 2.5*/Object getBean(String name, Object... args) throws BeansException;/*** Return the bean instance that uniquely matches the given object type, if any.* <p>This method goes into {@link ListableBeanFactory} by-type lookup territory* but may also be translated into a conventional by-name lookup based on the name* of the given type. For more extensive retrieval operations across sets of beans,* use {@link ListableBeanFactory} and/or {@link BeanFactoryUtils}.* @param requiredType type the bean must match; can be an interface or superclass.* {@code null} is disallowed.* @return an instance of the single bean matching the required type* @throws NoSuchBeanDefinitionException if no bean of the given type was found* @throws NoUniqueBeanDefinitionException if more than one bean of the given type was found* @throws BeansException if the bean could not be created* @since 3.0* @see ListableBeanFactory*/<T> T getBean(Class<T> requiredType) throws BeansException;/*** Return an instance, which may be shared or independent, of the specified bean.* <p>Allows for specifying explicit constructor arguments / factory method arguments,* overriding the specified default arguments (if any) in the bean definition.* <p>This method goes into {@link ListableBeanFactory} by-type lookup territory* but may also be translated into a conventional by-name lookup based on the name* of the given type. For more extensive retrieval operations across sets of beans,* use {@link ListableBeanFactory} and/or {@link BeanFactoryUtils}.* @param requiredType type the bean must match; can be an interface or superclass.* {@code null} is disallowed.* @param args arguments to use when creating a bean instance using explicit arguments* (only applied when creating a new instance as opposed to retrieving an existing one)* @return an instance of the bean* @throws NoSuchBeanDefinitionException if there is no such bean definition* @throws BeanDefinitionStoreException if arguments have been given but* the affected bean isn't a prototype* @throws BeansException if the bean could not be created* @since 4.1*/<T> T getBean(Class<T> requiredType, Object... args) throws BeansException;/*** Does this bean factory contain a bean definition or externally registered singleton* instance with the given name?* <p>If the given name is an alias, it will be translated back to the corresponding* canonical bean name.* <p>If this factory is hierarchical, will ask any parent factory if the bean cannot* be found in this factory instance.* <p>If a bean definition or singleton instance matching the given name is found,* this method will return {@code true} whether the named bean definition is concrete* or abstract, lazy or eager, in scope or not. Therefore, note that a {@code true}* return value from this method does not necessarily indicate that {@link #getBean}* will be able to obtain an instance for the same name.* @param name the name of the bean to query* @return whether a bean with the given name is present*/boolean containsBean(String name);/*** Is this bean a shared singleton? That is, will {@link #getBean} always* return the same instance?* <p>Note: This method returning {@code false} does not clearly indicate* independent instances. It indicates non-singleton instances, which may correspond* to a scoped bean as well. Use the {@link #isPrototype} operation to explicitly* check for independent instances.* <p>Translates aliases back to the corresponding canonical bean name.* Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the name of the bean to query* @return whether this bean corresponds to a singleton instance* @throws NoSuchBeanDefinitionException if there is no bean with the given name* @see #getBean* @see #isPrototype*/boolean isSingleton(String name) throws NoSuchBeanDefinitionException;/*** Is this bean a prototype? That is, will {@link #getBean} always return* independent instances?* <p>Note: This method returning {@code false} does not clearly indicate* a singleton object. It indicates non-independent instances, which may correspond* to a scoped bean as well. Use the {@link #isSingleton} operation to explicitly* check for a shared singleton instance.* <p>Translates aliases back to the corresponding canonical bean name.* Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the name of the bean to query* @return whether this bean will always deliver independent instances* @throws NoSuchBeanDefinitionException if there is no bean with the given name* @since 2.0.3* @see #getBean* @see #isSingleton*/boolean isPrototype(String name) throws NoSuchBeanDefinitionException;/*** Check whether the bean with the given name matches the specified type.* More specifically, check whether a {@link #getBean} call for the given name* would return an object that is assignable to the specified target type.* <p>Translates aliases back to the corresponding canonical bean name.* Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the name of the bean to query* @param typeToMatch the type to match against (as a {@code ResolvableType})* @return {@code true} if the bean type matches,* {@code false} if it doesn't match or cannot be determined yet* @throws NoSuchBeanDefinitionException if there is no bean with the given name* @since 4.2* @see #getBean* @see #getType*/boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException;/*** Check whether the bean with the given name matches the specified type.* More specifically, check whether a {@link #getBean} call for the given name* would return an object that is assignable to the specified target type.* <p>Translates aliases back to the corresponding canonical bean name.* Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the name of the bean to query* @param typeToMatch the type to match against (as a {@code Class})* @return {@code true} if the bean type matches,* {@code false} if it doesn't match or cannot be determined yet* @throws NoSuchBeanDefinitionException if there is no bean with the given name* @since 2.0.1* @see #getBean* @see #getType*/boolean isTypeMatch(String name, Class<?> typeToMatch) throws NoSuchBeanDefinitionException;/*** Determine the type of the bean with the given name. More specifically,* determine the type of object that {@link #getBean} would return for the given name.* <p>For a {@link FactoryBean}, return the type of object that the FactoryBean creates,* as exposed by {@link FactoryBean#getObjectType()}.* <p>Translates aliases back to the corresponding canonical bean name.* Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the name of the bean to query* @return the type of the bean, or {@code null} if not determinable* @throws NoSuchBeanDefinitionException if there is no bean with the given name* @since 1.1.2* @see #getBean* @see #isTypeMatch*/Class<?> getType(String name) throws NoSuchBeanDefinitionException;/*** Return the aliases for the given bean name, if any.* All of those aliases point to the same bean when used in a {@link #getBean} call.* <p>If the given name is an alias, the corresponding original bean name* and other aliases (if any) will be returned, with the original bean name* being the first element in the array.* <p>Will ask the parent factory if the bean cannot be found in this factory instance.* @param name the bean name to check for aliases* @return the aliases, or an empty array if none* @see #getBean*/String[] getAliases(String name);}

从接口中的方法名可以很容易的理解每个方法的意图，最常用或者最常见的就是getBean方法，用于获取Bean的实例。BeanFactory是用于访问Spring Bean容器的根接口，是一个单纯的Bean工厂，也就是常说的IOC容器的顶层定义，各种IOC容器是在其基础上为了满足不同需求而扩展的，包括经常使用的ApplicationContext。

DefaultListableBeanFactory是整个Bean加载的核心部分，是Spring注册及加载Bean的默认实现。下面列出了DefaultListableBeanFactory源代码中两个重要的属性，

    /** Map of bean definition objects, keyed by bean name */private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(256);/** List of bean definition names, in registration order */private volatile List<String> beanDefinitionNames = new ArrayList<String>(256);

其中，bean的定义被解析成 BeanDefinition，同时解析得到 beanName，将beanName和BeanDefinition存储到beanDefinitionMap中，同时会将beanName存储到beanDefinitionNames中。