Spring版本

5.2.5.RELEASE

参考

源码解读

BeanDefinitionRegistry继承了AliasRegistry接口，其核心子类有三个：

SimpleBeanDefinitionRegistry
DefaultListableBeanFactory
GenericApplicationContext

1 AliasRegistry

public interface AliasRegistry {

    /**
     * Given a name, register an alias for it.
     * @param name the canonical name
     * @param alias the alias to be registered
     * @throws IllegalStateException if the alias is already in use
     * and may not be overridden
     */
    void registerAlias(String name, String alias);

    /**
     * Remove the specified alias from this registry.
     * @param alias the alias to remove
     * @throws IllegalStateException if no such alias was found
     */
    void removeAlias(String alias);

    /**
     * Determine whether the given name is defined as an alias
     * (as opposed to the name of an actually registered component).
     * @param name the name to check
     * @return whether the given name is an alias
     */
    boolean isAlias(String name);

    /**
     * Return the aliases for the given name, if defined.
     * @param name the name to check for aliases
     * @return the aliases, or an empty array if none
     */
    String[] getAliases(String name);

}

该接口定义了四个方法：

registerAlias：为name注册alias别名
removeAlias：移除别名
isAlias：判断name是否被定义为别名
getAliases：获取name对应的所有别名

2 BeanDefinitionRegistry

public interface BeanDefinitionRegistry extends AliasRegistry {

    /**
     * Register a new bean definition with this registry.
     * Must support RootBeanDefinition and ChildBeanDefinition.
     * @param beanName the name of the bean instance to register
     * @param beanDefinition definition of the bean instance to register
     * @throws BeanDefinitionStoreException if the BeanDefinition is invalid
     * @throws BeanDefinitionOverrideException if there is already a BeanDefinition
     * for the specified bean name and we are not allowed to override it
     * @see GenericBeanDefinition
     * @see RootBeanDefinition
     * @see ChildBeanDefinition
     */
    void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException;

    /**
     * Remove the BeanDefinition for the given name.
     * @param beanName the name of the bean instance to register
     * @throws NoSuchBeanDefinitionException if there is no such bean definition
     */
    void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;

    /**
     * Return the BeanDefinition for the given bean name.
     * @param beanName name of the bean to find a definition for
     * @return the BeanDefinition for the given name (never {@code null})
     * @throws NoSuchBeanDefinitionException if there is no such bean definition
     */
    BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;

    /**
     * Check if this registry contains a bean definition with the given name.
     * @param beanName the name of the bean to look for
     * @return if this registry contains a bean definition with the given name
     */
    boolean containsBeanDefinition(String beanName);

    /**
     * Return the names of all beans defined in this registry.
     * @return the names of all beans defined in this registry,
     * or an empty array if none defined
     */
    String[] getBeanDefinitionNames();

    /**
     * Return the number of beans defined in the registry.
     * @return the number of beans defined in the registry
     */
    int getBeanDefinitionCount();

    /**
     * Determine whether the given bean name is already in use within this registry,
     * i.e. whether there is a local bean or alias registered under this name.
     * @param beanName the name to check
     * @return whether the given bean name is already in use
     */
    boolean isBeanNameInUse(String beanName);

}

BeanDefinitionRegistry继承自AliasRegistry，提供了一系列关于beanDefinition注册的接口定义

3 SimpleBeanDefinitionRegistry

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 {

        Assert.hasText(beanName, "'beanName' must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");
        this.beanDefinitionMap.put(beanName, beanDefinition);
    }

    @Override
    public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
        if (this.beanDefinitionMap.remove(beanName) == null) {
            throw new NoSuchBeanDefinitionException(beanName);
        }
    }

    @Override
    public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
        BeanDefinition bd = this.beanDefinitionMap.get(beanName);
        if (bd == null) {
            throw new NoSuchBeanDefinitionException(beanName);
        }
        return bd;
    }

    @Override
    public boolean containsBeanDefinition(String beanName) {
        return this.beanDefinitionMap.containsKey(beanName);
    }

    @Override
    public String[] getBeanDefinitionNames() {
        return StringUtils.toStringArray(this.beanDefinitionMap.keySet());
    }

    @Override
    public int getBeanDefinitionCount() {
        return this.beanDefinitionMap.size();
    }

    @Override
    public boolean isBeanNameInUse(String beanName) {
        return isAlias(beanName) || containsBeanDefinition(beanName);
    }

}

SimpleBeanDefinitionRegistry是BeanDefinitionRegistry的一个简单实现，可以看到
SimpleBeanDefinitionRegistry内部维护了一个ConcurrentHashMap对象beanDefinitionMap，beanDefinition的注册、移除等相关操作其实就是对beanDefinitionMap的操作。

4 DefaultListableBeanFactory

DefaultListableBeanFactory，ConfigurableListableBeanFactory（其实就是 BeanFactory ）和BeanDefinitionRegistry接口的默认实现：一个基于BeanDefinition元数据的完整 bean 工厂。所以相对于SimpleBeanDefinitionRegistry而言，DefaultListableBeanFactory则是一个具有注册功能的完整 Bean 工厂。它同样是用ConcurrentHashMap数据结构来存储注册的 BeanDefinition。具体逻辑可以查看《Spring源码解析（六）-解析bean标签》 3.1 节

5 GenericApplicationContext

    @Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        this.beanFactory.registerBeanDefinition(beanName, beanDefinition);
    }

    @Override
    public void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
        this.beanFactory.removeBeanDefinition(beanName);
    }

对于类GenericApplicationContext，查看源码你会发现他实现注册、注销功能都是委托DefaultListableBeanFactory实现的。

总结

BeanRegistry的逻辑是比较简单，不外乎就是将信息保存到一个map中，并没有想象中的复杂和高大上。

Spring源码解析（二十一）-BeanDefinition 注册表：BeanDefinitionRegistry