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1.IOC容器的祖先----BeanFactory接口

BeanFactory是Spring IOC中重要的一个顶层接口。它是工厂模式的产物，里面定义了一些对bean操作的方法。在其子接口进行了扩展。它有三个重要的子接口分别是ListableBeanFactory、HierarchicalBeanFactory、AutowireCapableBeanFactory。它们最终都由一个子类进行实现，就是DefaultListableBeanFactory，它实现了所有的接口。

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 name) 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 getBean(String name, @Nullable Class
    
      requiredType) throws BeansException;	Object getBean(String name, Object... args) throws BeansException;	
     
       T getBean(Class
      
        requiredType) throws BeansException;	
       
         T getBean(Class
        
          requiredType, Object... args) throws BeansException; //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 name); //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 name) throws NoSuchBeanDefinitionException; boolean isPrototype(String name) throws NoSuchBeanDefinitionException; boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException; boolean isTypeMatch(String name, @Nullable Class
          typeToMatch) throws NoSuchBeanDefinitionException; //得到bean实例的Class类型 @Nullable Class
          getType(String name) 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 name);}
        
       
      
     
    
   

2.IOC容器的集大成者----DefaultListableBeanFactory

如果说BeanFactory接口是IOC容器的祖先，那么DefaultListableBeanFactory就是IOC容器的集大成者。它是一个成熟完善的bean  factory。为什么它要实现所有接口呢？阅读Spring源码注释我们知道，每个接口都有它使用的场合，主要是为了区分在Spring内部操作过程中对象的传递和转化，对对象的数据访问所做的限制。它里面有个重要的方法registerBeanDefinition()，它是向容器注册解析好的BeanDefinition。

//向IOC容器注册解析的BeanDefiniton	@Override	public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)			throws BeanDefinitionStoreException {		Assert.hasText(beanName, "Bean name must not be empty");		Assert.notNull(beanDefinition, "BeanDefinition must not be null");		//校验解析的BeanDefiniton		if (beanDefinition instanceof AbstractBeanDefinition) {			try {				((AbstractBeanDefinition) beanDefinition).validate();			}			catch (BeanDefinitionValidationException ex) {				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,						"Validation of bean definition failed", ex);			}		}		BeanDefinition oldBeanDefinition;		oldBeanDefinition = this.beanDefinitionMap.get(beanName);		if (oldBeanDefinition != null) {			if (!isAllowBeanDefinitionOverriding()) {				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,						"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +						"': There is already [" + oldBeanDefinition + "] bound.");			}			else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE				if (this.logger.isWarnEnabled()) {					this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +							"' with a framework-generated bean definition: replacing [" +							oldBeanDefinition + "] with [" + beanDefinition + "]");				}			}			else if (!beanDefinition.equals(oldBeanDefinition)) {				if (this.logger.isInfoEnabled()) {					this.logger.info("Overriding bean definition for bean '" + beanName +							"' with a different definition: replacing [" + oldBeanDefinition +							"] with [" + beanDefinition + "]");				}			}			else {				if (this.logger.isDebugEnabled()) {					this.logger.debug("Overriding bean definition for bean '" + beanName +							"' with an equivalent definition: replacing [" + oldBeanDefinition +							"] with [" + beanDefinition + "]");				}			}			this.beanDefinitionMap.put(beanName, beanDefinition);		}		else {			if (hasBeanCreationStarted()) {				// Cannot modify startup-time collection elements anymore (for stable iteration)				//注册的过程中需要线程同步，以保证数据的一致性				synchronized (this.beanDefinitionMap) {					this.beanDefinitionMap.put(beanName, beanDefinition);					List
   
     updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);					updatedDefinitions.addAll(this.beanDefinitionNames);					updatedDefinitions.add(beanName);					this.beanDefinitionNames = updatedDefinitions;					if (this.manualSingletonNames.contains(beanName)) {						Set
    
      updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);						updatedSingletons.remove(beanName);						this.manualSingletonNames = updatedSingletons;					}				}			}			else {				// Still in startup registration phase				this.beanDefinitionMap.put(beanName, beanDefinition);				this.beanDefinitionNames.add(beanName);				this.manualSingletonNames.remove(beanName);			}			this.frozenBeanDefinitionNames = null;		}		//检查是否有同名的BeanDefinition已经在IOC容器中注册		if (oldBeanDefinition != null || containsSingleton(beanName)) {			//重置所有已经注册过的BeanDefinition的缓存			resetBeanDefinition(beanName);		}	}
    
   

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