【Spring源码】 BeanFactory和FactoryBean是什么？

/**
 * // 访问Spring bean容器的根接口
 * The root interface for accessing a Spring bean container.
 *
 * ......
 *
 * // 这个接口是由拥有许多bean定义的对象实现的，每个bean定义都由一个String名称唯一标识。
 * // 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)，或者返回单个共享实例(单例设计模式的高级替代方案，在单例设计模式中，
 * // 实例在工厂范围内是单例)。将返回哪种类型的实例取决于bean工厂配置。
 * <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).
 *
 * ......
 * 
 * // 通常，BeanFactory将加载存储在配置源(如XML文档)中的bean定义，并使用{@code org.springframework。Beans}包来配置bean。
 * // 但是，实现可以直接在Java代码中返回它根据需要创建的Java对象。对于如何存储定义没有限制:LDAP、RDBMS、XML、属性文件等等。
 * // 鼓励实现支持bean之间的引用(依赖注入)。
 * <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).
 *
 * ......
 * // Bean工厂实现应该尽可能支持标准的Bean生命周期接口。完整的初始化方法集及其标准顺序为：
 * <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:
 * <ol>
 * <li>BeanNameAware's {@code setBeanName}
 * <li>BeanClassLoaderAware's {@code setBeanClassLoader}
 * <li>BeanFactoryAware's {@code setBeanFactory}
 * <li>EnvironmentAware's {@code setEnvironment}
 * <li>EmbeddedValueResolverAware's {@code setEmbeddedValueResolver}
 * <li>ResourceLoaderAware's {@code setResourceLoader}
 * (only applicable when running in an application context)
 * <li>ApplicationEventPublisherAware's {@code setApplicationEventPublisher}
 * (only applicable when running in an application context)
 * <li>MessageSourceAware's {@code setMessageSource}
 * (only applicable when running in an application context)
 * <li>ApplicationContextAware's {@code setApplicationContext}
 * (only applicable when running in an application context)
 * <li>ServletContextAware's {@code setServletContext}
 * (only applicable when running in a web application context)
 * <li>{@code postProcessBeforeInitialization} methods of BeanPostProcessors
 * <li>InitializingBean's {@code afterPropertiesSet}
 * <li>a custom {@code init-method} definition
 * <li>{@code postProcessAfterInitialization} methods of BeanPostProcessors
 * </ol>
 *
 * <p>On shutdown of a bean factory, the following lifecycle methods apply:
 * <ol>
 * <li>{@code postProcessBeforeDestruction} methods of DestructionAwareBeanPostProcessors
 * <li>DisposableBean's {@code destroy}
 * <li>a custom {@code destroy-method} definition
 * </ol>
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 13 April 2001
 * @see BeanNameAware#setBeanName
 * @see BeanClassLoaderAware#setBeanClassLoader
 * @see BeanFactoryAware#setBeanFactory
 * @see org.springframework.context.EnvironmentAware#setEnvironment
 * @see org.springframework.context.EmbeddedValueResolverAware#setEmbeddedValueResolver
 * @see org.springframework.context.ResourceLoaderAware#setResourceLoader
 * @see org.springframework.context.ApplicationEventPublisherAware#setApplicationEventPublisher
 * @see org.springframework.context.MessageSourceAware#setMessageSource
 * @see org.springframework.context.ApplicationContextAware#setApplicationContext
 * @see org.springframework.web.context.ServletContextAware#setServletContext
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization
 * @see InitializingBean#afterPropertiesSet
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getInitMethodName
 * @see org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization
 * @see org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor#postProcessBeforeDestruction
 * @see DisposableBean#destroy
 * @see org.springframework.beans.factory.support.RootBeanDefinition#getDestroyMethodName
 */
public interface BeanFactory {
    ......
}

public interface BeanFactory {

   // 对FactoryBean的转义定义，因为如果使用bean的名字检索FactoryBean得到的对象是工厂生成的对象，
   // 如果需要得到工厂本身，需要转义
    String FACTORY_BEAN_PREFIX = "&";
    
    // 根据bean的名字，获取在IOC容器中得到bean实例
    Object getBean(String var1) throws BeansException;
    
    // 根据bean的名字和Class类型来得到bean实例，增加了类型安全验证机制。
    <T> T getBean(String var1, Class<T> var2) throws BeansException;
    Object getBean(String var1, Object... var2) throws BeansException;
    <T> T getBean(Class<T> var1) throws BeansException;
    <T> T getBean(Class<T> var1, Object... var2) throws BeansException;
    <T> ObjectProvider<T> getBeanProvider(Class<T> var1);
    <T> ObjectProvider<T> getBeanProvider(ResolvableType var1);

    // 提供对bean的检索，看看是否在IOC容器有这个名字的bean
    boolean containsBean(String var1);

    // 根据bean名字得到bean实例，并同时判断这个bean是不是单例
    boolean isSingleton(String var1) throws NoSuchBeanDefinitionException;
    boolean isPrototype(String var1) throws NoSuchBeanDefinitionException;
    boolean isTypeMatch(String var1, ResolvableType var2) throws NoSuchBeanDefinitionException;
    boolean isTypeMatch(String var1, Class<?> var2) throws NoSuchBeanDefinitionException;

    // 得到bean实例的Class类型
    @Nullable
    Class<?> getType(String var1) throws NoSuchBeanDefinitionException;

    // 得到bean的别名，如果根据别名检索，那么其原名也会被检索出来
    String[] getAliases(String var1);
}

/**
 * // 由{@link BeanFactory}中使用的对象实现的接口，这些对象本身就是单个对象的工厂。
 * // 如果一个bean实现了这个接口，那么它将被用作要公开的对象的工厂，而不是直接用作将自己公开的bean实例。
 * 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.
 *
 * // 注意:实现该接口的bean不能作为普通bean使用。
 * // FactoryBean是以bean风格定义的，但是为bean引用公开的对象({@link #getObject()})始终是它创建的对象。
 * <p><b>NB: A bean that implements this interface cannot be used as a normal bean.</b>
 * A FactoryBean is defined in a bean style, but the object exposed for bean
 * references ({@link #getObject()}) is always the object that it creates.
 * ......
 *
 * // 该接口在框架本身中被大量使用，例如用于AOP {@link org.springframework.jndi.JndiObjectFactoryBean}。
 * // 它也可以用于定制组件;但是，这只在基础结构代码中常见。
 * <p>This interface is heavily used within the framework itself, for example for
 * the AOP {@link org.springframework.aop.framework.ProxyFactoryBean} or the
 * {@link org.springframework.jndi.JndiObjectFactoryBean}. It can be used for
 * custom components as well; however, this is only common for infrastructure code.
 * ......
 *
 * // 最后，FactoryBean对象参与了包含BeanFactory的bean创建的同步。
 * // 除了在FactoryBean本身(或类似)内进行惰性初始化之外，通常不需要内部同步。
 * <p>Finally, FactoryBean objects participate in the containing BeanFactory's
 * synchronization of bean creation. There is usually no need for internal
 * synchronization other than for purposes of lazy initialization within the
 * FactoryBean itself (or the like).
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 08.03.2003
 * @param <T> the bean type
 * @see org.springframework.beans.factory.BeanFactory
 * @see org.springframework.aop.framework.ProxyFactoryBean
 * @see org.springframework.jndi.JndiObjectFactoryBean
 */
public interface FactoryBean<T> {
    ......
}

public interface FactoryBean<T> {

   // 获取容器管理的对象实例
   @Nullable
   T getObject() throws Exception;

   // 获取Bean工厂创建的对象类型
   @Nullable
   Class<?> getObjectType();

   // Bean工厂创建的对象是否单例模式，
   // 如果是，则整个容器中只有一个实例对象，每次请求都返回同一个实例对象
   default boolean isSingleton() {
      return true;
   }

}