Spring源码笔记之SpringIOC--（2）从BeanDefinition到Bean实例

从BeanDefinition到Bean实例

对比SimpleBeanDefinitionRegistry和DefaultListableBeanFactory的源码，中间省略一些无关紧要的逻辑：

SimpleBeanDefinitionRegistry.java

java 复制代码

public class SimpleBeanDefinitionRegistry extends SimpleAliasRegistry implements BeanDefinitionRegistry {

	/** Map of bean definition objects, keyed by bean name. */
	private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(64);
    
    @Override
	public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {
		this.beanDefinitionMap.put(beanName, beanDefinition);
    }
    
	@Override
	public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
		BeanDefinition bd = this.beanDefinitionMap.get(beanName);
		if (bd == null) {
			throw new NoSuchBeanDefinitionException(beanName);
		}
		return bd;
	}
}

DefaultListableBeanFactory.java

java 复制代码

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
		implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
	/** Map of bean definition objects, keyed by bean name. */
	private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);
    @Override
	public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {
        // 实现比较复杂暂时省略
    }
    
	@Override
	public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
        // 实现比较复杂暂时省略
	}
    
    @Override
    public Object getBean(String name) throws BeansException {
		assertBeanFactoryActive();
		return getBeanFactory().getBean(name);
	}
    
    @Override
	public <T> T getBean(Class<T> requiredType) throws BeansException {
		return getBean(requiredType, (Object[]) null);
	}
}

从类关系上来看DefaultListableBeanFactory不单单实现了BeanDefinitionRegistry，还实现了BeanFactory（继承了AbstractAutowireCapableBeanFactory）提供了获取bean实例的方法。分析其继承关系如下:
<<interface>> BeanDefinitionRegistry 注册BeanDefinition接口 <<interface>> BeanFactory ioc容器核心接口 <<interface>> ListableBeanFactory BeanFactory扩展，提供获取所有Bean的能力 <<interface>> AutowireCapableBeanFactory BeanFactory扩展，提供自动注入的能力 <<interface>> HierarchicalBeanFactory BeanFactory扩展，提供访问父容器的功能 <<interface>> ConfigurableBeanFactory 提供配置BeanFactory的能力 <<interface>> ConfigurableListableBeanFactory 提供配置、分析和修改bean定义，以及预实例化单例能力 DefaultListableBeanFactory Spring默认的BeanFactory实现

其中BeanFactory是IOC容器的核心